已完成“选课候补与自动递补”完整流程。

学生端：满员后可加入/取消候补，展示候补顺位和当前候补人数。自动递补：退课释放名额后，按候补时间顺序重新校验学籍、范围、学分及时间冲突；不合格者自动失效并继续下一位。管理端：教学班显示候补人数，名单抽屉提供候补队列及移出操作。状态通知：递补成功、资格失效、批次关闭、管理员移出均会通知学生。并发安全：退课和递补放在 Serializable 事务中执行。数据库：已补充 SQLite 开发迁移和 MySQL 正式迁移。
2026-07-26 15:39:50 +08:00
parent 65eed820a7
commit 56b13b3adb
12 changed files with 1203 additions and 79 deletions
@@ -2,7 +2,7 @@

 面向普通高校的教务管理系统。后端使用 ASP.NET Core 10、EF Core 10，前端使用 Vue 3、TypeScript 和 Element Plus。

-当前已实现系统登录与角色权限、基础数据、用户管理、教师档案、学生档案、课程库、培养方案、教学任务、排课课表、学生选课、成绩管理、考试考场、学籍异动、毕业审核、学位授予、毕业离校和首页统计。人员及课程列表支持组合筛选、服务端分页和完整增删改查；培养方案支持课程模块、专业年级版本、复制新版本、发布与旧版本归档，已发布版本可继续维护名称、学分说明和课程结构，适用专业、入学年级及版本号保持锁定；教学任务支持学期课程开设、多教师、合班、容量校验、发布与结课，公共课由校级教务负责、专业必修/专业选修/实践课下放课程所属学院管理，并支持教师按学期申报授课科目、学院审核授课资格、公共课按若干行政班合并教学班，以及在审核通过的教师池中随机均衡分配后批量生成草稿；排课支持学期作息维护、单双周与周次节次、课程可用时间、校区/教学楼/指定教室约束、不占用教室课程、教室容量、教师/行政班/教室冲突校验、自动生成、手工微调和版本化发布；选课支持批次时间窗、投放范围、容量与学分上限、重复课程与课表冲突校验、退课截止时间和实时教学班名单；成绩管理支持分项比例、批量录入、特殊考试状态、自动总评与绩点、教师提交、学院审核、校级发布和学生成绩单；考试管理支持考试计划、场次、考场容量、监考教师、考生名单以及考场/监考/学生时间冲突校验；学籍异动支持休学、复学、退学申请，辅导员、学院、学校三级顺序审核，学生撤回，以及最终审批后自动同步学籍状态；毕业审核按入学年级匹配已发布培养方案，以正式成绩计算总学分、必修通过和未解决不及格课程，支持学院范围查看、人工复核、校级锁定发布和学生结果查询；学位授予以已发布毕业资格为来源，按正式成绩加权平均绩点生成规则结论，支持学院人工复核、校级发布锁定和学生结果查询；毕业离校支持自定义事项与责任部门，按校级、学院、辅导员角色分工办理，强制数据范围校验，学生进度查询，以及必办事项全部完成后的批次锁定。
+当前已实现系统登录与角色权限、基础数据、用户管理、教师档案、学生档案、课程库、培养方案、教学任务、排课课表、学生选课、成绩管理、考试考场、学籍异动、毕业审核、学位授予、毕业离校和首页统计。人员及课程列表支持组合筛选、服务端分页和完整增删改查；培养方案支持课程模块、专业年级版本、复制新版本、发布与旧版本归档，已发布版本可继续维护名称、学分说明和课程结构，适用专业、入学年级及版本号保持锁定；教学任务支持学期课程开设、多教师、合班、容量校验、发布与结课，公共课由校级教务负责、专业必修/专业选修/实践课下放课程所属学院管理，并支持教师按学期申报授课科目、学院审核授课资格、公共课按若干行政班合并教学班，以及在审核通过的教师池中随机均衡分配后批量生成草稿；排课支持学期作息维护、单双周与周次节次、课程可用时间、校区/教学楼/指定教室约束、不占用教室课程、教室容量、教师/行政班/教室冲突校验、自动生成、手工微调和版本化发布；选课支持批次时间窗、投放范围、容量与学分上限、重复课程与课表冲突校验、退课截止时间、满员候补、顺位查询、退课后资格复核与自动递补，以及正式名单和候补队列管理；成绩管理支持分项比例、批量录入、特殊考试状态、自动总评与绩点、教师提交、学院审核、校级发布和学生成绩单；考试管理支持考试计划、场次、考场容量、监考教师、考生名单以及考场/监考/学生时间冲突校验；学籍异动支持休学、复学、退学申请，辅导员、学院、学校三级顺序审核，学生撤回，以及最终审批后自动同步学籍状态；毕业审核按入学年级匹配已发布培养方案，以正式成绩计算总学分、必修通过和未解决不及格课程，支持学院范围查看、人工复核、校级锁定发布和学生结果查询；学位授予以已发布毕业资格为来源，按正式成绩加权平均绩点生成规则结论，支持学院人工复核、校级发布锁定和学生结果查询；毕业离校支持自定义事项与责任部门，按校级、学院、辅导员角色分工办理，强制数据范围校验，学生进度查询，以及必办事项全部完成后的批次锁定。

 课程库支持下载标准模板后批量导入 `.xlsx`，按课程编码新增或更新，并在整批校验失败时不写入任何课程；授课资格既支持教师申报后审核，也支持学院在本院教师范围内直接分配；学生可在“我的培养方案”中查看本人适用的已发布方案，并按已完成、在读、重修中、未通过、待完成和未修读状态核对课程与学分进度。

@@ -153,12 +153,51 @@ public sealed class CourseSelectionsController(
    [Authorize(Roles = RoundManagers)]
    public async Task<ActionResult> CloseRound(Guid id, CancellationToken cancellationToken)
    {
-        var round = await db.CourseSelectionRounds.FindAsync([id], cancellationToken);
+        return await db.ExecuteInRetriableTransactionAsync<ActionResult>(
+            async transaction =>
+            {
+                db.ChangeTracker.Clear();
+                var round = await db.CourseSelectionRounds
+                    .FirstOrDefaultAsync(x => x.Id == id, cancellationToken);
                if (round is null) return NotFound();
                if (round.Status != CourseSelectionRoundStatus.Open)
                    return ConflictProblem("只有开放中的选课批次可以关闭。");
+
+                var waitlisted = await db.CourseEnrollments
+                    .Include(x => x.Student)
+                    .Include(x => x.CourseSelectionOffering)
+                    .ThenInclude(x => x!.TeachingTask)
+                    .ThenInclude(x => x!.Course)
+                    .Where(x =>
+                        x.CourseSelectionOffering!.CourseSelectionRoundId == id &&
+                        x.Status == CourseEnrollmentStatus.Waitlisted)
+                    .ToListAsync(cancellationToken);
+                var now = DateTime.UtcNow;
+                foreach (var enrollment in waitlisted)
+                {
+                    enrollment.Status = CourseEnrollmentStatus.Expired;
+                    enrollment.WithdrawnAt = now;
+                    if (enrollment.Student!.UserId is Guid userId)
+                    {
+                        db.Notifications.Add(new Notification
+                        {
+                            UserId = userId,
+                            Title = "课程候补已结束",
+                            Content =
+                                $"“{enrollment.CourseSelectionOffering!.TeachingTask!.Course!.Name}”" +
+                                "选课批次已关闭，本次候补未获得名额。",
+                            LinkUrl = "/course-selections"
+                        });
+                    }
+                }
+
                round.Status = CourseSelectionRoundStatus.Closed;
-        return await SaveAsync(id, false, cancellationToken);
+                await db.SaveChangesAsync(cancellationToken);
+                await transaction.CommitAsync(cancellationToken);
+                return Ok(new { ExpiredWaitlistCount = waitlisted.Count });
+            },
+            cancellationToken,
+            IsolationLevel.Serializable);
    }

    [HttpGet("rounds/{roundId:guid}/offerings")]
@@ -193,6 +232,8 @@ public sealed class CourseSelectionsController(
                x.Capacity,
                EnrolledCount = x.Enrollments.Count(item =>
                    item.Status == CourseEnrollmentStatus.Enrolled),
+                WaitlistedCount = x.Enrollments.Count(item =>
+                    item.Status == CourseEnrollmentStatus.Waitlisted),
                x.IsOpenToAll,
                x.Notes,
                x.UpdatedAt
@@ -318,6 +359,36 @@ public sealed class CourseSelectionsController(
                x.EnrolledAt
            })
            .ToListAsync(cancellationToken);
+        var waitlistedRows = await db.CourseEnrollments.AsNoTracking()
+            .Where(x =>
+                x.CourseSelectionOfferingId == id &&
+                x.Status == CourseEnrollmentStatus.Waitlisted)
+            .OrderBy(x => x.WaitlistedAt)
+            .ThenBy(x => x.CreatedAt)
+            .Select(x => new
+            {
+                x.Id,
+                x.StudentId,
+                x.Student!.StudentNumber,
+                x.Student.Name,
+                ClassName = x.Student.AdministrativeClass!.Name,
+                MajorName = x.Student.AdministrativeClass.Major!.Name,
+                x.WaitlistedAt
+            })
+            .ToListAsync(cancellationToken);
+        var waitlist = waitlistedRows
+            .Select((item, index) => new
+            {
+                item.Id,
+                item.StudentId,
+                item.StudentNumber,
+                item.Name,
+                item.ClassName,
+                item.MajorName,
+                item.WaitlistedAt,
+                Position = index + 1
+            })
+            .ToList();
        return Ok(new
        {
            offering.Id,
@@ -330,6 +401,13 @@ public sealed class CourseSelectionsController(
            offering.Capacity,
            EnrolledCount = students.Count,
            Students = students,
+            WaitlistedCount = waitlist.Count,
+            Waitlist = waitlist,
+            CanManageWaitlist =
+                offering.RoundStatus == CourseSelectionRoundStatus.Open &&
+                (scope.IsInRole(SystemRoles.SuperAdmin) ||
+                 scope.IsInRole(SystemRoles.AcademicAdmin) ||
+                 scope.IsInRole(SystemRoles.CollegeAdmin)),
            CanProxyEnroll =
                CourseSelectionRules.SupportsProxyEnrollment(offering.CourseNature) &&
                offering.RoundStatus != CourseSelectionRoundStatus.Draft &&
@@ -550,19 +628,28 @@ public sealed class CourseSelectionsController(
                        x.StudentId == student.Id);
                    if (enrollment is null)
                    {
-                        db.CourseEnrollments.Add(new CourseEnrollment
+                        enrollment = new CourseEnrollment
                        {
                            CourseSelectionOfferingId = id,
                            StudentId = student.Id,
                            EnrolledAt = now
-                        });
+                        };
+                        db.CourseEnrollments.Add(enrollment);
                    }
                    else
                    {
                        enrollment.Status = CourseEnrollmentStatus.Enrolled;
                        enrollment.EnrolledAt = now;
+                        enrollment.WaitlistedAt = null;
                        enrollment.WithdrawnAt = null;
                    }
+                    await ExpireOtherWaitlistsForCourseAsync(
+                        student.Id,
+                        task.CourseId,
+                        round.AcademicTermId,
+                        enrollment.Id,
+                        now,
+                        cancellationToken);
                }

                await db.SaveChangesAsync(cancellationToken);
@@ -633,21 +720,30 @@ public sealed class CourseSelectionsController(
                        .FirstOrDefault(x => x.StudentId == student.Id);
                    if (enrollment is null)
                    {
-                        db.CourseEnrollments.Add(new CourseEnrollment
+                        enrollment = new CourseEnrollment
                        {
                            CourseSelectionOfferingId = offeringId,
                            StudentId = student.Id,
                            EnrollmentType = EnrollmentType.Retake,
                            EnrolledAt = now
-                        });
+                        };
+                        db.CourseEnrollments.Add(enrollment);
                    }
                    else
                    {
                        enrollment.Status = CourseEnrollmentStatus.Enrolled;
                        enrollment.EnrolledAt = now;
+                        enrollment.WaitlistedAt = null;
                        enrollment.WithdrawnAt = null;
                        enrollment.EnrollmentType = EnrollmentType.Retake;
                    }
+                    await ExpireOtherWaitlistsForCourseAsync(
+                        student.Id,
+                        task.CourseId,
+                        round.AcademicTermId,
+                        enrollment.Id,
+                        now,
+                        cancellationToken);
                    enrolled++;
                }

@@ -666,7 +762,13 @@ public sealed class CourseSelectionsController(
        Guid enrollmentId,
        CancellationToken cancellationToken)
    {
+        return await db.ExecuteInRetriableTransactionAsync<ActionResult>(
+            async transaction =>
+            {
+                db.ChangeTracker.Clear();
                var enrollment = await db.CourseEnrollments
+                    .Include(x => x.CourseSelectionOffering)
+                    .ThenInclude(x => x!.CourseSelectionRound)
                    .Include(x => x.CourseSelectionOffering)
                    .ThenInclude(x => x!.TeachingTask)
                    .ThenInclude(x => x!.Course)
@@ -687,7 +789,66 @@ public sealed class CourseSelectionsController(

                enrollment.Status = CourseEnrollmentStatus.Withdrawn;
                enrollment.WithdrawnAt = DateTime.UtcNow;
-        return await SaveAsync(enrollmentId, false, cancellationToken);
+                await db.SaveChangesAsync(cancellationToken);
+                var promoted = await PromoteNextWaitlistedAsync(
+                    offering,
+                    cancellationToken);
+                await db.SaveChangesAsync(cancellationToken);
+                await transaction.CommitAsync(cancellationToken);
+                return Ok(new { PromotedStudentId = promoted?.StudentId });
+            },
+            cancellationToken,
+            IsolationLevel.Serializable);
+    }
+
+    [HttpDelete("offerings/{offeringId:guid}/waitlist/{enrollmentId:guid}")]
+    [Authorize(Roles = OfferingManagers)]
+    public async Task<ActionResult> AdminCancelWaitlist(
+        Guid offeringId,
+        Guid enrollmentId,
+        CancellationToken cancellationToken)
+    {
+        return await db.ExecuteInRetriableTransactionAsync<ActionResult>(
+            async transaction =>
+            {
+                db.ChangeTracker.Clear();
+                if (!await ScopedOfferings().AnyAsync(
+                        x => x.Id == offeringId,
+                        cancellationToken))
+                    return NotFound();
+                var enrollment = await db.CourseEnrollments
+                    .Include(x => x.Student)
+                    .Include(x => x.CourseSelectionOffering)
+                    .ThenInclude(x => x!.TeachingTask)
+                    .ThenInclude(x => x!.Course)
+                    .FirstOrDefaultAsync(
+                        x =>
+                            x.Id == enrollmentId &&
+                            x.CourseSelectionOfferingId == offeringId &&
+                            x.Status == CourseEnrollmentStatus.Waitlisted,
+                        cancellationToken);
+                if (enrollment is null) return NotFound();
+
+                enrollment.Status = CourseEnrollmentStatus.Cancelled;
+                enrollment.WithdrawnAt = DateTime.UtcNow;
+                if (enrollment.Student!.UserId is Guid userId)
+                {
+                    db.Notifications.Add(new Notification
+                    {
+                        UserId = userId,
+                        Title = "课程候补已取消",
+                        Content =
+                            $"管理员已将你移出“{enrollment.CourseSelectionOffering!.TeachingTask!.Course!.Name}”" +
+                            "候补队列。",
+                        LinkUrl = "/course-selections"
+                    });
+                }
+                await db.SaveChangesAsync(cancellationToken);
+                await transaction.CommitAsync(cancellationToken);
+                return NoContent();
+            },
+            cancellationToken,
+            IsolationLevel.Serializable);
    }

    [HttpGet("student/options")]
@@ -724,6 +885,8 @@ public sealed class CourseSelectionsController(
                x.Capacity,
                x.Enrollments.Count(item =>
                    item.Status == CourseEnrollmentStatus.Enrolled),
+                x.Enrollments.Count(item =>
+                    item.Status == CourseEnrollmentStatus.Waitlisted),
                x.IsOpenToAll,
                 x.Enrollments
                     .Where(item => item.StudentId == student.Id)
@@ -732,6 +895,8 @@ public sealed class CourseSelectionsController(
                 x.TeachingTask.SchedulingMode == TeachingTaskSchedulingMode.Flexible,
                 db.CourseEnrollments.Any(e =>
                     e.StudentId == student.Id &&
+                     (e.Status == CourseEnrollmentStatus.Enrolled ||
+                      e.Status == CourseEnrollmentStatus.Withdrawn) &&
                     e.CourseSelectionOffering!.TeachingTask!.CourseId ==
                         x.TeachingTask.CourseId &&
                     e.CourseSelectionOffering.CourseSelectionRound!.AcademicTermId !=
@@ -751,9 +916,48 @@ public sealed class CourseSelectionsController(
                        entry.EndWeek,
                        entry.WeekPattern,
                        entry.Classroom == null ? "不占用教室" : entry.Classroom.Name))
-                    .ToList()))
+                    .ToList(),
+                null))
            .ToListAsync(cancellationToken);

+        var waitlistedOfferingIds = offerings
+            .Where(x => x.EnrollmentStatus == CourseEnrollmentStatus.Waitlisted)
+            .Select(x => x.Id)
+            .ToArray();
+        if (waitlistedOfferingIds.Length > 0)
+        {
+            var queueRows = await db.CourseEnrollments.AsNoTracking()
+                .Where(x => x.Status == CourseEnrollmentStatus.Waitlisted)
+                .WhereIn(waitlistedOfferingIds, x => x.CourseSelectionOfferingId)
+                .Select(x => new
+                {
+                    x.CourseSelectionOfferingId,
+                    x.StudentId,
+                    x.WaitlistedAt,
+                    x.CreatedAt
+                })
+                .ToListAsync(cancellationToken);
+            var positions = queueRows
+                .GroupBy(x => x.CourseSelectionOfferingId)
+                .SelectMany(group => group
+                    .OrderBy(x => x.WaitlistedAt)
+                    .ThenBy(x => x.CreatedAt)
+                    .Select((item, index) => new
+                    {
+                        item.CourseSelectionOfferingId,
+                        item.StudentId,
+                        Position = index + 1
+                    }))
+                .Where(x => x.StudentId == student.Id)
+                .ToDictionary(x => x.CourseSelectionOfferingId, x => x.Position);
+            offerings = offerings
+                .Select(x => x with
+                {
+                    WaitlistPosition = positions.GetValueOrDefault(x.Id)
+                })
+                .ToList();
+        }
+
        return Ok(new
        {
            Round = new
@@ -816,9 +1020,11 @@ public sealed class CourseSelectionsController(
                x.Status,
                x.EnrollmentType,
                x.EnrolledAt,
+                x.WaitlistedAt,
                x.WithdrawnAt,
                CanWithdraw =
-                    x.Status == CourseEnrollmentStatus.Enrolled &&
+                    (x.Status == CourseEnrollmentStatus.Enrolled ||
+                     x.Status == CourseEnrollmentStatus.Waitlisted) &&
                    x.CourseSelectionOffering.CourseSelectionRound.Status ==
                        CourseSelectionRoundStatus.Open &&
                    DateTime.UtcNow <=
@@ -866,6 +1072,8 @@ public sealed class CourseSelectionsController(
                var isRetake = await db.CourseEnrollments.AnyAsync(
                    x =>
                        x.StudentId == student.Id &&
+                        (x.Status == CourseEnrollmentStatus.Enrolled ||
+                         x.Status == CourseEnrollmentStatus.Withdrawn) &&
                        x.CourseSelectionOffering!.TeachingTask!.CourseId == task.CourseId &&
                        x.CourseSelectionOffering.CourseSelectionRound!.AcademicTermId !=
                            round.AcademicTermId,
@@ -884,9 +1092,9 @@ public sealed class CourseSelectionsController(
                        x.CourseSelectionOfferingId == offering.Id &&
                        x.Status == CourseEnrollmentStatus.Enrolled,
                    cancellationToken);
-                var effectiveCapacity = isRetake
-                    ? CourseSelectionRules.RetakeCapacity(offering.Capacity)
-                    : offering.Capacity;
+                var effectiveCapacity = CourseSelectionRules.EffectiveCapacity(
+                    offering.Capacity,
+                    isRetake);
                if (enrolledCount >= effectiveCapacity)
                    return ConflictProblem("该教学班名额已满。");

@@ -967,9 +1175,17 @@ public sealed class CourseSelectionsController(
                {
                    existing.Status = CourseEnrollmentStatus.Enrolled;
                    existing.EnrolledAt = now;
+                    existing.WaitlistedAt = null;
                    existing.WithdrawnAt = null;
                    existing.EnrollmentType = isRetake ? EnrollmentType.Retake : EnrollmentType.Normal;
                }
+                await ExpireOtherWaitlistsForCourseAsync(
+                    student.Id,
+                    task.CourseId,
+                    round.AcademicTermId,
+                    existing.Id,
+                    now,
+                    cancellationToken);
                await db.SaveChangesAsync(cancellationToken);
                await transaction.CommitAsync(cancellationToken);
                return Created(string.Empty, new { existing.Id, IsRetake = isRetake });
@@ -978,28 +1194,168 @@ public sealed class CourseSelectionsController(
            IsolationLevel.Serializable);
    }

+    [HttpPost("student/waitlist")]
+    [Authorize(Roles = SystemRoles.Student)]
+    public async Task<ActionResult> JoinWaitlist(
+        StudentEnrollmentRequest request,
+        CancellationToken cancellationToken)
+    {
+        return await db.ExecuteInRetriableTransactionAsync<ActionResult>(
+            async transaction =>
+            {
+                db.ChangeTracker.Clear();
+                var student = await CurrentStudentAsync(cancellationToken);
+                if (student is null) return ProfileNotFound();
+
+                var offering = await db.CourseSelectionOfferings
+                    .Include(x => x.CourseSelectionRound)
+                    .Include(x => x.TeachingTask)
+                    .ThenInclude(x => x!.Course)
+                    .Include(x => x.TeachingTask)
+                    .ThenInclude(x => x!.Classes)
+                    .FirstOrDefaultAsync(x => x.Id == request.OfferingId, cancellationToken);
+                if (offering is null) return NotFound();
+                var round = offering.CourseSelectionRound!;
+                var now = DateTime.UtcNow;
+                if (!CourseSelectionRules.IsSelectionOpen(round, now))
+                    return ConflictProblem("当前不在该选课批次的开放时间内。");
+
+                var existing = await db.CourseEnrollments.FirstOrDefaultAsync(
+                    x =>
+                        x.CourseSelectionOfferingId == offering.Id &&
+                        x.StudentId == student.Id,
+                    cancellationToken);
+                if (existing?.Status == CourseEnrollmentStatus.Enrolled)
+                    return ConflictProblem("你已经选择了该教学班。");
+                if (existing?.Status == CourseEnrollmentStatus.Waitlisted)
+                    return ConflictProblem("你已经在该教学班的候补队列中。");
+
+                var eligibility = await EvaluateEnrollmentEligibilityAsync(
+                    student,
+                    offering,
+                    cancellationToken);
+                if (eligibility.Error is not null)
+                    return ConflictProblem(eligibility.Error);
+
+                var sameCourseWaitlistExists = await db.CourseEnrollments.AnyAsync(
+                    x =>
+                        x.StudentId == student.Id &&
+                        x.Status == CourseEnrollmentStatus.Waitlisted &&
+                        x.CourseSelectionOffering!.TeachingTask!.CourseId ==
+                            offering.TeachingTask!.CourseId &&
+                        x.CourseSelectionOffering.CourseSelectionRound!.AcademicTermId ==
+                            round.AcademicTermId,
+                    cancellationToken);
+                if (sameCourseWaitlistExists)
+                    return ConflictProblem("你已在本学期同一课程的其他教学班候补。");
+
+                var enrolledCount = await db.CourseEnrollments.CountAsync(
+                    x =>
+                        x.CourseSelectionOfferingId == offering.Id &&
+                        x.Status == CourseEnrollmentStatus.Enrolled,
+                    cancellationToken);
+                var effectiveCapacity = CourseSelectionRules.EffectiveCapacity(
+                    offering.Capacity,
+                    eligibility.IsRetake);
+                if (enrolledCount < effectiveCapacity)
+                    return ConflictProblem("该教学班当前仍有名额，请直接选择课程。");
+
+                if (existing is null)
+                {
+                    existing = new CourseEnrollment
+                    {
+                        CourseSelectionOfferingId = offering.Id,
+                        StudentId = student.Id,
+                        Status = CourseEnrollmentStatus.Waitlisted,
+                        EnrollmentType = eligibility.IsRetake
+                            ? EnrollmentType.Retake
+                            : EnrollmentType.Normal,
+                        WaitlistedAt = now
+                    };
+                    db.CourseEnrollments.Add(existing);
+                }
+                else
+                {
+                    existing.Status = CourseEnrollmentStatus.Waitlisted;
+                    existing.EnrollmentType = eligibility.IsRetake
+                        ? EnrollmentType.Retake
+                        : EnrollmentType.Normal;
+                    existing.WaitlistedAt = now;
+                    existing.WithdrawnAt = null;
+                }
+
+                await db.SaveChangesAsync(cancellationToken);
+                var position = await db.CourseEnrollments.CountAsync(
+                    x =>
+                        x.CourseSelectionOfferingId == offering.Id &&
+                        x.Status == CourseEnrollmentStatus.Waitlisted &&
+                        x.WaitlistedAt <= now,
+                    cancellationToken);
+                await transaction.CommitAsync(cancellationToken);
+                return Accepted(new
+                {
+                    existing.Id,
+                    Status = CourseEnrollmentStatus.Waitlisted,
+                    Position = position,
+                    IsRetake = eligibility.IsRetake
+                });
+            },
+            cancellationToken,
+            IsolationLevel.Serializable);
+    }
+
    [HttpDelete("student/enrollments/{id:guid}")]
    [Authorize(Roles = SystemRoles.Student)]
    public async Task<ActionResult> Withdraw(Guid id, CancellationToken cancellationToken)
    {
+        return await db.ExecuteInRetriableTransactionAsync<ActionResult>(
+            async transaction =>
+            {
+                db.ChangeTracker.Clear();
                var student = await CurrentStudentAsync(cancellationToken);
                if (student is null) return ProfileNotFound();
                var enrollment = await db.CourseEnrollments
                    .Include(x => x.CourseSelectionOffering)
                    .ThenInclude(x => x!.CourseSelectionRound)
+                    .Include(x => x.CourseSelectionOffering)
+                    .ThenInclude(x => x!.TeachingTask)
+                    .ThenInclude(x => x!.Course)
                    .FirstOrDefaultAsync(
                        x => x.Id == id && x.StudentId == student.Id,
                        cancellationToken);
                if (enrollment is null) return NotFound();
-        if (enrollment.Status != CourseEnrollmentStatus.Enrolled)
-            return ConflictProblem("该课程已经退选。");
+                var wasEnrolled = enrollment.Status == CourseEnrollmentStatus.Enrolled;
+                var wasWaitlisted =
+                    enrollment.Status == CourseEnrollmentStatus.Waitlisted;
+                if (!wasEnrolled && !wasWaitlisted)
+                    return ConflictProblem("该课程已经退选或候补已经结束。");
                if (!CourseSelectionRules.CanWithdraw(
                        enrollment.CourseSelectionOffering!.CourseSelectionRound!,
                        DateTime.UtcNow))
-            return ConflictProblem("当前批次已停止退课。");
-        enrollment.Status = CourseEnrollmentStatus.Withdrawn;
+                    return ConflictProblem("当前批次已停止退课和候补调整。");
+
+                enrollment.Status = wasWaitlisted
+                    ? CourseEnrollmentStatus.Cancelled
+                    : CourseEnrollmentStatus.Withdrawn;
                enrollment.WithdrawnAt = DateTime.UtcNow;
-        return await SaveAsync(id, false, cancellationToken);
+                await db.SaveChangesAsync(cancellationToken);
+                CourseEnrollment? promoted = null;
+                if (wasEnrolled)
+                {
+                    promoted = await PromoteNextWaitlistedAsync(
+                        enrollment.CourseSelectionOffering,
+                        cancellationToken);
+                    await db.SaveChangesAsync(cancellationToken);
+                }
+                await transaction.CommitAsync(cancellationToken);
+                return Ok(new
+                {
+                    CancelledWaitlist = wasWaitlisted,
+                    PromotedStudentId = promoted?.StudentId
+                });
+            },
+            cancellationToken,
+            IsolationLevel.Serializable);
    }

    [HttpGet("my-offerings")]
@@ -1178,6 +1534,214 @@ public sealed class CourseSelectionsController(
            .ToListAsync(cancellationToken);
    }

+    private async Task<EnrollmentEligibility> EvaluateEnrollmentEligibilityAsync(
+        Student student,
+        CourseSelectionOffering offering,
+        CancellationToken cancellationToken)
+    {
+        var round = offering.CourseSelectionRound!;
+        var task = offering.TeachingTask!;
+        if (student.Status != StudentStatus.Active)
+            return new(false, "只有在籍学生可以选课或候补。");
+        if (task.Status != TeachingTaskStatus.Published)
+            return new(false, "该教学班当前不可选。");
+        if (!offering.IsOpenToAll &&
+            !await db.TeachingTaskClasses.AnyAsync(
+                x =>
+                    x.TeachingTaskId == task.Id &&
+                    x.AdministrativeClassId == student.AdministrativeClassId,
+                cancellationToken))
+            return new(false, "你不属于该教学班的选课对象。");
+
+        var isRetake = await db.CourseEnrollments.AnyAsync(
+            x =>
+                x.StudentId == student.Id &&
+                (x.Status == CourseEnrollmentStatus.Enrolled ||
+                 x.Status == CourseEnrollmentStatus.Withdrawn) &&
+                x.CourseSelectionOffering!.TeachingTask!.CourseId == task.CourseId &&
+                x.CourseSelectionOffering.CourseSelectionRound!.AcademicTermId !=
+                    round.AcademicTermId,
+            cancellationToken);
+        if (!isRetake)
+        {
+            var duplicateCourse = await db.CourseEnrollments.AnyAsync(
+                x =>
+                    x.StudentId == student.Id &&
+                    x.Status == CourseEnrollmentStatus.Enrolled &&
+                    x.CourseSelectionOffering!.TeachingTask!.CourseId == task.CourseId &&
+                    x.CourseSelectionOffering.CourseSelectionRound!.AcademicTermId ==
+                        round.AcademicTermId,
+                cancellationToken);
+            if (duplicateCourse)
+                return new(false, "同一学期不能重复选择相同课程。");
+        }
+
+        var selectedCredits = await db.CourseEnrollments
+            .Where(x =>
+                x.StudentId == student.Id &&
+                x.Status == CourseEnrollmentStatus.Enrolled &&
+                x.CourseSelectionOffering!.CourseSelectionRoundId == round.Id)
+            .SumAsync(
+                x => (decimal?)x.CourseSelectionOffering!.TeachingTask!.Course!.Credits,
+                cancellationToken) ?? 0;
+        if (selectedCredits + task.Course!.Credits > round.MaxCredits)
+        {
+            return new(
+                isRetake,
+                $"获得名额后将达到 {selectedCredits + task.Course.Credits:0.#} 学分，" +
+                $"超过本轮 {round.MaxCredits:0.#} 学分上限。");
+        }
+
+        var candidateEntries = await PublishedScheduleEntries(
+            round.AcademicTermId,
+            [task.Id],
+            cancellationToken);
+        if (CourseSelectionRules.RequiresPublishedSchedule(task.SchedulingMode) &&
+            candidateEntries.Count == 0)
+            return new(isRetake, "该教学班尚未发布课表，暂时不能选课或候补。");
+
+        var selectedTaskIds = await db.CourseEnrollments.AsNoTracking()
+            .Where(x =>
+                x.StudentId == student.Id &&
+                x.Status == CourseEnrollmentStatus.Enrolled &&
+                x.CourseSelectionOffering!.CourseSelectionRound!.AcademicTermId ==
+                    round.AcademicTermId)
+            .Select(x => x.CourseSelectionOffering!.TeachingTaskId)
+            .Distinct()
+            .ToArrayAsync(cancellationToken);
+        var selectedEntries = await PublishedScheduleEntries(
+            round.AcademicTermId,
+            selectedTaskIds,
+            cancellationToken);
+        if (CourseSelectionRules.HasScheduleConflict(candidateEntries, selectedEntries))
+        {
+            if (!isRetake)
+                return new(false, "该教学班与已选课程的上课时间冲突。");
+            var overlap = CourseSelectionRules.CalculateScheduleOverlap(
+                candidateEntries,
+                selectedEntries);
+            if (overlap > 50)
+            {
+                return new(
+                    true,
+                    $"重修课程时间冲突 {overlap:F0}%，超过 50% 上限。");
+            }
+        }
+
+        return new(isRetake, null);
+    }
+
+    private async Task<CourseEnrollment?> PromoteNextWaitlistedAsync(
+        CourseSelectionOffering offering,
+        CancellationToken cancellationToken)
+    {
+        var round = offering.CourseSelectionRound!;
+        if (!CourseSelectionRules.CanPromoteWaitlist(round, DateTime.UtcNow))
+            return null;
+
+        var waitlist = await db.CourseEnrollments
+            .Include(x => x.Student)
+            .ThenInclude(x => x!.AdministrativeClass)
+            .Where(x =>
+                x.CourseSelectionOfferingId == offering.Id &&
+                x.Status == CourseEnrollmentStatus.Waitlisted)
+            .OrderBy(x => x.WaitlistedAt)
+            .ThenBy(x => x.CreatedAt)
+            .ToListAsync(cancellationToken);
+        if (waitlist.Count == 0) return null;
+
+        var enrolledCount = await db.CourseEnrollments.CountAsync(
+            x =>
+                x.CourseSelectionOfferingId == offering.Id &&
+                x.Status == CourseEnrollmentStatus.Enrolled,
+            cancellationToken);
+        var now = DateTime.UtcNow;
+        foreach (var candidate in waitlist)
+        {
+            var eligibility = await EvaluateEnrollmentEligibilityAsync(
+                candidate.Student!,
+                offering,
+                cancellationToken);
+            if (eligibility.Error is not null)
+            {
+                candidate.Status = CourseEnrollmentStatus.Expired;
+                candidate.WithdrawnAt = now;
+                if (candidate.Student!.UserId is Guid invalidUserId)
+                {
+                    db.Notifications.Add(new Notification
+                    {
+                        UserId = invalidUserId,
+                        Title = "课程候补已失效",
+                        Content =
+                            $"“{offering.TeachingTask!.Course!.Name}”候补未能递补：" +
+                            eligibility.Error,
+                        LinkUrl = "/course-selections"
+                    });
+                }
+                continue;
+            }
+
+            var effectiveCapacity = CourseSelectionRules.EffectiveCapacity(
+                offering.Capacity,
+                eligibility.IsRetake);
+            if (enrolledCount >= effectiveCapacity)
+                continue;
+
+            candidate.Status = CourseEnrollmentStatus.Enrolled;
+            candidate.EnrollmentType = eligibility.IsRetake
+                ? EnrollmentType.Retake
+                : EnrollmentType.Normal;
+            candidate.EnrolledAt = now;
+            candidate.WithdrawnAt = null;
+            await ExpireOtherWaitlistsForCourseAsync(
+                candidate.StudentId,
+                offering.TeachingTask!.CourseId,
+                round.AcademicTermId,
+                candidate.Id,
+                now,
+                cancellationToken);
+            if (candidate.Student!.UserId is Guid userId)
+            {
+                db.Notifications.Add(new Notification
+                {
+                    UserId = userId,
+                    Title = "课程候补递补成功",
+                    Content =
+                        $"“{offering.TeachingTask.Course!.Name}”已释放名额，" +
+                        "你已自动进入正式选课名单。",
+                    LinkUrl = "/course-selections"
+                });
+            }
+            return candidate;
+        }
+
+        return null;
+    }
+
+    private async Task ExpireOtherWaitlistsForCourseAsync(
+        Guid studentId,
+        Guid courseId,
+        Guid academicTermId,
+        Guid retainedEnrollmentId,
+        DateTime now,
+        CancellationToken cancellationToken)
+    {
+        var otherWaitlists = await db.CourseEnrollments
+            .Where(x =>
+                x.Id != retainedEnrollmentId &&
+                x.StudentId == studentId &&
+                x.Status == CourseEnrollmentStatus.Waitlisted &&
+                x.CourseSelectionOffering!.TeachingTask!.CourseId == courseId &&
+                x.CourseSelectionOffering.CourseSelectionRound!.AcademicTermId ==
+                    academicTermId)
+            .ToListAsync(cancellationToken);
+        foreach (var waitlist in otherWaitlists)
+        {
+            waitlist.Status = CourseEnrollmentStatus.Expired;
+            waitlist.WithdrawnAt = now;
+        }
+    }
+
    private async Task<ActionResult> SaveAsync(
        Guid id,
        bool created,
@@ -1207,6 +1771,8 @@ public sealed class CourseSelectionsController(

    private static string? Normalize(string? value) =>
        string.IsNullOrWhiteSpace(value) ? null : value.Trim();
+
+    private sealed record EnrollmentEligibility(bool IsRetake, string? Error);
 }

 public sealed record CourseSelectionRoundRequest(
@@ -1242,11 +1808,13 @@ public sealed record StudentOfferingDto(
    IEnumerable<string> TeacherNames,
    int Capacity,
    int EnrolledCount,
+    int WaitlistedCount,
     bool IsOpenToAll,
     CourseEnrollmentStatus? EnrollmentStatus,
     bool IsFlexible,
     bool IsRetake,
-     IEnumerable<StudentScheduleDto> Schedules);
+     IEnumerable<StudentScheduleDto> Schedules,
+     int? WaitlistPosition);

 public sealed record StudentScheduleDto(
    int DayOfWeek,
@@ -38,6 +38,7 @@ public sealed class CourseEnrollment : EntityBase
    public CourseEnrollmentStatus Status { get; set; } = CourseEnrollmentStatus.Enrolled;
    public EnrollmentType EnrollmentType { get; set; } = EnrollmentType.Normal;
    public DateTime EnrolledAt { get; set; } = DateTime.UtcNow;
+    public DateTime? WaitlistedAt { get; set; }
    public DateTime? WithdrawnAt { get; set; }
 }

@@ -51,7 +52,10 @@ public enum CourseSelectionRoundStatus
 public enum CourseEnrollmentStatus
 {
    Enrolled = 1,
-    Withdrawn = 2
+    Withdrawn = 2,
+    Waitlisted = 3,
+    Cancelled = 4,
+    Expired = 5
 }

 public enum EnrollmentType
@@ -14,6 +14,10 @@ public static class CourseSelectionRules
        round.Status == CourseSelectionRoundStatus.Open &&
        nowUtc <= round.WithdrawalEndsAt;

+    public static bool CanPromoteWaitlist(CourseSelectionRound round, DateTime nowUtc) =>
+        round.Status == CourseSelectionRoundStatus.Open &&
+        nowUtc <= round.WithdrawalEndsAt;
+
    public static bool SupportsProxyEnrollment(CourseNature nature) =>
        nature == CourseNature.GeneralRequired;

@@ -68,4 +72,7 @@ public static class CourseSelectionRules
    /// <summary>Retake expanded capacity: ceiling(original * 1.15).</summary>
    public static int RetakeCapacity(int originalCapacity) =>
        (int)Math.Ceiling(originalCapacity * 1.15);
+
+    public static int EffectiveCapacity(int originalCapacity, bool isRetake) =>
+        isRetake ? RetakeCapacity(originalCapacity) : originalCapacity;
 }
@@ -500,6 +500,12 @@ public sealed class AppDbContext(DbContextOptions<AppDbContext> options)
            entity.HasIndex(x => new { x.CourseSelectionOfferingId, x.StudentId })
                .IsUnique();
            entity.HasIndex(x => new { x.StudentId, x.Status });
+            entity.HasIndex(x => new
+            {
+                x.CourseSelectionOfferingId,
+                x.Status,
+                x.WaitlistedAt
+            });
            entity.HasOne(x => x.CourseSelectionOffering)
                .WithMany(x => x.Enrollments)
                .HasForeignKey(x => x.CourseSelectionOfferingId)
@@ -48,6 +48,8 @@ public sealed class DevelopmentSqliteMigrator(
        "20260725_25_academic_warnings";
    private const string AcademicTermArchivingMigration =
        "20260726_27_academic_term_archiving";
+    private const string CourseSelectionWaitlistMigration =
+        "20260726_28_course_selection_waitlist";

    public async Task MigrateAsync(CancellationToken cancellationToken = default)
    {
@@ -344,6 +346,19 @@ public sealed class DevelopmentSqliteMigrator(
            AcademicTermArchivingMigration,
            academicTermArchivingExists ? [] : AcademicTermArchivingStatements,
            cancellationToken);
+
+        var courseSelectionWaitlistExists = await db.Database
+            .SqlQueryRaw<int>(
+                """
+                SELECT COUNT(*) AS "Value"
+                FROM pragma_table_info('CourseEnrollments')
+                WHERE name = 'WaitlistedAt'
+                """)
+            .AnyAsync(value => value > 0, cancellationToken);
+        await ApplyMigrationAsync(
+            CourseSelectionWaitlistMigration,
+            courseSelectionWaitlistExists ? [] : CourseSelectionWaitlistStatements,
+            cancellationToken);
    }

    private async Task ApplyMigrationAsync(
@@ -1589,6 +1604,18 @@ public sealed class DevelopmentSqliteMigrator(
        """
    ];

+    private static readonly string[] CourseSelectionWaitlistStatements =
+    [
+        """
+        ALTER TABLE "CourseEnrollments"
+        ADD COLUMN "WaitlistedAt" TEXT NULL;
+        """,
+        """
+        CREATE INDEX IF NOT EXISTS "IX_CourseEnrollments_CourseSelectionOfferingId_Status_WaitlistedAt"
+        ON "CourseEnrollments" ("CourseSelectionOfferingId", "Status", "WaitlistedAt");
+        """
+    ];
+
    private static readonly string[] CourseAdjustmentsStatements =
    [
        """
@@ -0,0 +1,37 @@
+using Jiaowu.Api.Infrastructure.Persistence;
+using Microsoft.EntityFrameworkCore.Infrastructure;
+using Microsoft.EntityFrameworkCore.Migrations;
+
+#nullable disable
+
+namespace Jiaowu.Api.Infrastructure.Persistence.Migrations.MySql;
+
+[DbContext(typeof(AppDbContext))]
+[Migration("20260726170000_CourseSelectionWaitlist")]
+public partial class CourseSelectionWaitlist : Migration
+{
+    protected override void Up(MigrationBuilder migrationBuilder)
+    {
+        migrationBuilder.AddColumn<DateTime>(
+            name: "WaitlistedAt",
+            table: "CourseEnrollments",
+            type: "datetime(6)",
+            nullable: true);
+
+        migrationBuilder.CreateIndex(
+            name: "IX_CourseEnrollments_CourseSelectionOfferingId_Status_WaitlistedAt",
+            table: "CourseEnrollments",
+            columns: new[] { "CourseSelectionOfferingId", "Status", "WaitlistedAt" });
+    }
+
+    protected override void Down(MigrationBuilder migrationBuilder)
+    {
+        migrationBuilder.DropIndex(
+            name: "IX_CourseEnrollments_CourseSelectionOfferingId_Status_WaitlistedAt",
+            table: "CourseEnrollments");
+
+        migrationBuilder.DropColumn(
+            name: "WaitlistedAt",
+            table: "CourseEnrollments");
+    }
+}
@@ -732,6 +732,9 @@ namespace Jiaowu.Api.Infrastructure.Persistence.Migrations.MySql
                    b.Property<DateTime>("UpdatedAt")
                        .HasColumnType("datetime(6)");

+                    b.Property<DateTime?>("WaitlistedAt")
+                        .HasColumnType("datetime(6)");
+
                    b.Property<DateTime?>("WithdrawnAt")
                        .HasColumnType("datetime(6)");

@@ -740,6 +743,8 @@ namespace Jiaowu.Api.Infrastructure.Persistence.Migrations.MySql
                    b.HasIndex("CourseSelectionOfferingId", "StudentId")
                        .IsUnique();

+                    b.HasIndex("CourseSelectionOfferingId", "Status", "WaitlistedAt");
+
                    b.HasIndex("StudentId", "Status");

                    b.ToTable("CourseEnrollments");
@@ -31,6 +31,21 @@ public sealed class CourseSelectionRulesTests
        Assert.False(CourseSelectionRules.CanWithdraw(round, now.AddHours(1)));
    }

+    [Fact]
+    public void Waitlist_promotion_uses_withdrawal_window_and_retake_capacity()
+    {
+        var now = new DateTime(2026, 7, 24, 8, 0, 0, DateTimeKind.Utc);
+        var round = CreateRound(now.AddHours(-1), now.AddHours(1));
+        round.WithdrawalEndsAt = now.AddHours(2);
+
+        Assert.True(CourseSelectionRules.CanPromoteWaitlist(round, now));
+        Assert.Equal(60, CourseSelectionRules.EffectiveCapacity(60, false));
+        Assert.Equal(69, CourseSelectionRules.EffectiveCapacity(60, true));
+
+        round.Status = CourseSelectionRoundStatus.Closed;
+        Assert.False(CourseSelectionRules.CanPromoteWaitlist(round, now));
+    }
+
    [Fact]
    public void Schedule_conflict_detects_overlapping_weeks_and_periods()
    {
@@ -0,0 +1,303 @@
+using Jiaowu.Api.Controllers;
+using Jiaowu.Api.Domain.Academic;
+using Jiaowu.Api.Domain.Identity;
+using Jiaowu.Api.Infrastructure.Auth;
+using Jiaowu.Api.Infrastructure.Persistence;
+using Microsoft.AspNetCore.Mvc;
+using Microsoft.Data.Sqlite;
+using Microsoft.EntityFrameworkCore;
+
+namespace Jiaowu.Api.Tests;
+
+public sealed class CourseSelectionsControllerTests
+{
+    [Fact]
+    public async Task Withdrawal_skips_invalid_waiter_and_promotes_next_student()
+    {
+        await using var connection = new SqliteConnection("Data Source=:memory:");
+        await connection.OpenAsync();
+        var options = new DbContextOptionsBuilder<AppDbContext>()
+            .UseSqlite(connection)
+            .Options;
+        await using var db = new AppDbContext(options);
+        await db.Database.EnsureCreatedAsync();
+        var data = await SeedFullOfferingAsync(db);
+
+        var firstController = new CourseSelectionsController(
+            db,
+            new StudentDataScope(data.FirstWaiterUserId));
+        var firstResult = await firstController.JoinWaitlist(
+            new StudentEnrollmentRequest(data.OfferingId),
+            CancellationToken.None);
+        Assert.IsType<AcceptedResult>(firstResult);
+
+        var secondController = new CourseSelectionsController(
+            db,
+            new StudentDataScope(data.SecondWaiterUserId));
+        var secondResult = await secondController.JoinWaitlist(
+            new StudentEnrollmentRequest(data.OfferingId),
+            CancellationToken.None);
+        Assert.IsType<AcceptedResult>(secondResult);
+
+        db.ChangeTracker.Clear();
+        var firstWaiter = await db.Students.SingleAsync(
+            x => x.UserId == data.FirstWaiterUserId);
+        firstWaiter.Status = StudentStatus.Suspended;
+        await db.SaveChangesAsync();
+
+        var enrolledController = new CourseSelectionsController(
+            db,
+            new StudentDataScope(data.EnrolledUserId));
+        var withdrawResult = await enrolledController.Withdraw(
+            data.EnrollmentId,
+            CancellationToken.None);
+        Assert.IsType<OkObjectResult>(withdrawResult);
+
+        db.ChangeTracker.Clear();
+        var enrollments = await db.CourseEnrollments
+            .OrderBy(x => x.StudentId)
+            .ToListAsync();
+        Assert.Equal(
+            CourseEnrollmentStatus.Withdrawn,
+            enrollments.Single(x => x.StudentId == data.EnrolledStudentId).Status);
+        Assert.Equal(
+            CourseEnrollmentStatus.Expired,
+            enrollments.Single(x => x.StudentId == data.FirstWaiterStudentId).Status);
+        Assert.Equal(
+            CourseEnrollmentStatus.Enrolled,
+            enrollments.Single(x => x.StudentId == data.SecondWaiterStudentId).Status);
+        Assert.Equal(
+            2,
+            await db.Notifications.CountAsync(x =>
+                x.Title == "课程候补已失效" ||
+                x.Title == "课程候补递补成功"));
+    }
+
+    [Fact]
+    public async Task Closing_round_expires_remaining_waitlist_and_notifies_student()
+    {
+        await using var connection = new SqliteConnection("Data Source=:memory:");
+        await connection.OpenAsync();
+        var options = new DbContextOptionsBuilder<AppDbContext>()
+            .UseSqlite(connection)
+            .Options;
+        await using var db = new AppDbContext(options);
+        await db.Database.EnsureCreatedAsync();
+        var data = await SeedFullOfferingAsync(db);
+
+        var studentController = new CourseSelectionsController(
+            db,
+            new StudentDataScope(data.FirstWaiterUserId));
+        Assert.IsType<AcceptedResult>(await studentController.JoinWaitlist(
+            new StudentEnrollmentRequest(data.OfferingId),
+            CancellationToken.None));
+
+        var adminController = new CourseSelectionsController(
+            db,
+            new AdminDataScope());
+        Assert.IsType<OkObjectResult>(await adminController.CloseRound(
+            data.RoundId,
+            CancellationToken.None));
+
+        db.ChangeTracker.Clear();
+        var waitlist = await db.CourseEnrollments.SingleAsync(
+            x => x.StudentId == data.FirstWaiterStudentId);
+        Assert.Equal(CourseEnrollmentStatus.Expired, waitlist.Status);
+        Assert.NotNull(waitlist.WithdrawnAt);
+        Assert.True(await db.Notifications.AnyAsync(x =>
+            x.UserId == data.FirstWaiterUserId &&
+            x.Title == "课程候补已结束"));
+    }
+
+    private static async Task<SeededSelection> SeedFullOfferingAsync(AppDbContext db)
+    {
+        var college = new College { Code = "CS", Name = "计算机学院" };
+        var major = new Major
+        {
+            Code = "080901",
+            Name = "计算机科学与技术",
+            CollegeId = college.Id,
+            DegreeType = "工学学士"
+        };
+        var administrativeClass = new AdministrativeClass
+        {
+            Code = "CS2026-01",
+            Name = "计科 2026-1 班",
+            MajorId = major.Id,
+            Grade = 2026
+        };
+        var term = new AcademicTerm
+        {
+            Code = "2026-1",
+            Name = "2026—2027 学年第一学期",
+            AcademicYear = "2026-2027",
+            Season = TermSeason.Autumn,
+            StartDate = new DateOnly(2026, 9, 1),
+            EndDate = new DateOnly(2027, 1, 20)
+        };
+        var course = new Course
+        {
+            Code = "CS101",
+            Name = "程序设计基础",
+            CollegeId = college.Id,
+            Credits = 4,
+            TotalHours = 64,
+            LectureHours = 48,
+            PracticeHours = 16,
+            Nature = CourseNature.MajorRequired,
+            AssessmentMethod = AssessmentMethod.Examination
+        };
+        var task = new TeachingTask
+        {
+            TaskNumber = "2026-1-CS101-01",
+            Name = "程序设计基础教学班",
+            AcademicTermId = term.Id,
+            CourseId = course.Id,
+            Capacity = 1,
+            SchedulingMode = TeachingTaskSchedulingMode.Flexible,
+            Status = TeachingTaskStatus.Published,
+            Classes =
+            [
+                new TeachingTaskClass
+                {
+                    AdministrativeClassId = administrativeClass.Id
+                }
+            ]
+        };
+        var round = new CourseSelectionRound
+        {
+            AcademicTermId = term.Id,
+            Name = "第一轮选课",
+            StartsAt = DateTime.UtcNow.AddHours(-1),
+            EndsAt = DateTime.UtcNow.AddHours(1),
+            WithdrawalEndsAt = DateTime.UtcNow.AddHours(2),
+            MaxCredits = 30,
+            Status = CourseSelectionRoundStatus.Open
+        };
+        var offering = new CourseSelectionOffering
+        {
+            CourseSelectionRoundId = round.Id,
+            TeachingTaskId = task.Id,
+            Capacity = 1
+        };
+        var enrolledUser = CreateUser("2026001", "已选学生");
+        var firstWaiterUser = CreateUser("2026002", "候补甲");
+        var secondWaiterUser = CreateUser("2026003", "候补乙");
+        var enrolledStudent = CreateStudent(
+            "2026001",
+            "已选学生",
+            enrolledUser.Id,
+            administrativeClass.Id);
+        var firstWaiter = CreateStudent(
+            "2026002",
+            "候补甲",
+            firstWaiterUser.Id,
+            administrativeClass.Id);
+        var secondWaiter = CreateStudent(
+            "2026003",
+            "候补乙",
+            secondWaiterUser.Id,
+            administrativeClass.Id);
+        var enrollment = new CourseEnrollment
+        {
+            CourseSelectionOfferingId = offering.Id,
+            StudentId = enrolledStudent.Id
+        };
+
+        db.Add(college);
+        await db.SaveChangesAsync();
+
+        db.AddRange(
+            major,
+            term,
+            course,
+            enrolledUser,
+            firstWaiterUser,
+            secondWaiterUser);
+        await db.SaveChangesAsync();
+
+        db.Add(administrativeClass);
+        await db.SaveChangesAsync();
+
+        db.AddRange(
+            enrolledStudent,
+            firstWaiter,
+            secondWaiter);
+        await db.SaveChangesAsync();
+
+        db.AddRange(task, round);
+        await db.SaveChangesAsync();
+
+        db.Add(offering);
+        await db.SaveChangesAsync();
+
+        db.Add(enrollment);
+        await db.SaveChangesAsync();
+        return new SeededSelection(
+            round.Id,
+            offering.Id,
+            enrollment.Id,
+            enrolledStudent.Id,
+            firstWaiter.Id,
+            secondWaiter.Id,
+            enrolledUser.Id,
+            firstWaiterUser.Id,
+            secondWaiterUser.Id);
+    }
+
+    private static ApplicationUser CreateUser(string userName, string displayName) =>
+        new()
+        {
+            Id = Guid.NewGuid(),
+            UserName = userName,
+            NormalizedUserName = userName,
+            DisplayName = displayName
+        };
+
+    private static Student CreateStudent(
+        string number,
+        string name,
+        Guid userId,
+        Guid classId) =>
+        new()
+        {
+            StudentNumber = number,
+            Name = name,
+            UserId = userId,
+            AdministrativeClassId = classId,
+            EnrollmentYear = 2026,
+            EnrollmentDate = new DateOnly(2026, 9, 1),
+            Status = StudentStatus.Active
+        };
+
+    private sealed class StudentDataScope(Guid userId) : ICurrentUserDataScope
+    {
+        public CurrentUserScope Current { get; } = new(
+            userId,
+            "测试学生",
+            null,
+            DataScope.Self,
+            new HashSet<string>([SystemRoles.Student]));
+    }
+
+    private sealed class AdminDataScope : ICurrentUserDataScope
+    {
+        public CurrentUserScope Current { get; } = new(
+            Guid.NewGuid(),
+            "测试管理员",
+            null,
+            DataScope.All,
+            new HashSet<string>([SystemRoles.SuperAdmin]));
+    }
+
+    private sealed record SeededSelection(
+        Guid RoundId,
+        Guid OfferingId,
+        Guid EnrollmentId,
+        Guid EnrolledStudentId,
+        Guid FirstWaiterStudentId,
+        Guid SecondWaiterStudentId,
+        Guid EnrolledUserId,
+        Guid FirstWaiterUserId,
+        Guid SecondWaiterUserId);
+}
@@ -8,7 +8,7 @@ namespace Jiaowu.Api.Tests;
 public sealed class MySqlMigrationTests
 {
    private const string LatestMigration =
-        "20260726022634_AttendanceCheckIn";
+        "20260726170000_CourseSelectionWaitlist";

    [Fact]
    public void Production_migration_is_discoverable_and_generates_mysql_sql()
@@ -27,6 +27,10 @@ public sealed class MySqlMigrationTests
        Assert.Contains("CREATE TABLE `WarningRules`", script);
        Assert.Contains("ADD `CheckInMethod` int NOT NULL DEFAULT 1", script);
        Assert.Contains("CREATE UNIQUE INDEX `IX_AttendanceSheets_CheckInToken`", script);
+        Assert.Contains("ADD `WaitlistedAt` datetime(6) NULL", script);
+        Assert.Contains(
+            "CREATE INDEX `IX_CourseEnrollments_CourseSelectionOfferingId_Status_WaitlistedAt`",
+            script);
        Assert.Contains("SET `ExamDate` = DATE(`StartsAt`)", script);
        Assert.Contains("DEFAULT 1", script);
        Assert.DoesNotContain("0001-01-01", script);
@@ -114,8 +114,8 @@ function conflictingSelectedCourses(offering: any) {
  return selectedOfferings.value
    .filter((selected) =>
      selected.id !== offering.id
-      && selected.schedules.some((existing: any) =>
-        offering.schedules.some((candidate: any) =>
+      && (selected.schedules ?? []).some((existing: any) =>
+        (offering.schedules ?? []).some((candidate: any) =>
          schedulesOverlap(candidate, existing),
        ),
      ),
@@ -123,14 +123,10 @@ function conflictingSelectedCourses(offering: any) {
    .map((item) => item.courseName)
 }

-function offeringBlockReason(offering: any) {
-  if (offering.enrollmentStatus === 'Enrolled') return ''
+function offeringEligibilityReason(offering: any) {
+  if (['Enrolled', 'Waitlisted'].includes(offering.enrollmentStatus)) return ''
  if (!selectedRound.value?.isAvailableNow) return '当前不在选课开放时间内'
-  const effectiveCap = offering.isRetake
-    ? Math.ceil(offering.capacity * 1.15)
-    : offering.capacity
-  if (offering.enrolledCount >= effectiveCap) return '教学班名额已满'
-  if (!offering.isFlexible && !offering.schedules.length) return '正式课表尚未发布'
+  if (!offering.isFlexible && !(offering.schedules ?? []).length) return '正式课表尚未发布'
  if (!offering.isRetake && selectedOfferings.value.some((item) =>
    item.id !== offering.id && item.courseCode === offering.courseCode,
  )) return '本学期已选择同一课程'
@@ -147,9 +143,26 @@ function offeringBlockReason(offering: any) {
  return ''
 }

+function effectiveCapacity(offering: any) {
+  return offering.isRetake
+    ? Math.ceil(offering.capacity * 1.15)
+    : offering.capacity
+}
+
+function isOfferingFull(offering: any) {
+  return offering.enrolledCount >= effectiveCapacity(offering)
+}
+
+function offeringBlockReason(offering: any) {
+  const eligibilityReason = offeringEligibilityReason(offering)
+  if (eligibilityReason) return eligibilityReason
+  if (isOfferingFull(offering)) return '教学班名额已满，可加入候补'
+  return ''
+}
+
 function calcRetakeOverlapOk(offering: any): boolean {
  let totalPeriods = 0, overlapPeriods = 0
-  for (const candidate of offering.schedules) {
+  for (const candidate of (offering.schedules ?? [])) {
    totalPeriods += candidate.periodCount
    for (const selected of selectedOfferings.value) {
      for (const existing of (selected.schedules ?? [])) {
@@ -179,12 +192,15 @@ const filteredOfferings = computed(() => {
    if (offeringStatus.value === 'Selected') {
      return offering.enrollmentStatus === 'Enrolled'
    }
-    const blocked = Boolean(offeringBlockReason(offering))
+    if (offeringStatus.value === 'Waitlisted') {
+      return offering.enrollmentStatus === 'Waitlisted'
+    }
+    const blocked = Boolean(offeringEligibilityReason(offering))
    if (offeringStatus.value === 'Selectable') {
-      return offering.enrollmentStatus !== 'Enrolled' && !blocked
+      return !['Enrolled', 'Waitlisted'].includes(offering.enrollmentStatus) && !blocked
    }
    if (offeringStatus.value === 'Blocked') {
-      return offering.enrollmentStatus !== 'Enrolled' && blocked
+      return !['Enrolled', 'Waitlisted'].includes(offering.enrollmentStatus) && blocked
    }
    return true
  })
@@ -328,6 +344,8 @@ async function loadRounds(keepSelection = true) {

 async function selectRound(round: any) {
  selectedRound.value = round
+  offerings.value = []
+  enrollments.value = []
  previewOfferingId.value = ''
  detailLoading.value = true
  try {
@@ -652,6 +670,25 @@ async function removeFromRoster(student: any) {
  }
 }

+async function removeFromWaitlist(student: any) {
+  if (!roster.value) return
+  try {
+    await ElMessageBox.confirm(
+      `确认将 ${student.studentNumber} ${student.name} 移出“${roster.value.courseName}”候补队列？`,
+      '调整候补队列',
+      { type: 'warning', confirmButtonText: '确认移出', cancelButtonText: '取消' },
+    )
+    await http.delete(
+      `/course-selections/offerings/${roster.value.id}/waitlist/${student.id}`,
+    )
+    ElMessage.success('已移出候补队列')
+    await loadRoster(roster.value.id)
+    if (selectedRound.value) await selectRound(selectedRound.value)
+  } catch (error: any) {
+    if (error !== 'cancel' && error !== 'close') ElMessage.error(apiErrorMessage(error))
+  }
+}
+
 async function enroll(offering: any) {
  try {
    await http.post('/course-selections/student/enrollments', {
@@ -664,6 +701,18 @@ async function enroll(offering: any) {
  }
 }

+async function joinWaitlist(offering: any) {
+  try {
+    const { data } = await http.post('/course-selections/student/waitlist', {
+      offeringId: offering.id,
+    })
+    ElMessage.success(`已加入“${offering.courseName}”候补，当前第 ${data.position} 位`)
+    await selectRound(selectedRound.value)
+  } catch (error) {
+    ElMessage.error(apiErrorMessage(error))
+  }
+}
+
 function togglePreview(offering: any) {
  previewOfferingId.value = previewOfferingId.value === offering.id
    ? ''
@@ -691,6 +740,27 @@ async function withdraw(offering: any) {
  }
 }

+async function cancelWaitlist(offering: any) {
+  const enrollment = enrollments.value.find(
+    (item) =>
+      item.courseSelectionOfferingId === offering.id &&
+      item.status === 'Waitlisted',
+  )
+  if (!enrollment) return
+  try {
+    await ElMessageBox.confirm(
+      `确定取消“${offering.courseName}”候补吗？取消后将失去当前顺位。`,
+      '取消候补',
+      { type: 'warning', confirmButtonText: '确认取消', cancelButtonText: '继续候补' },
+    )
+    await http.delete(`/course-selections/student/enrollments/${enrollment.id}`)
+    ElMessage.success('已取消候补')
+    await selectRound(selectedRound.value)
+  } catch (error: any) {
+    if (error !== 'cancel' && error !== 'close') ElMessage.error(apiErrorMessage(error))
+  }
+}
+
 onMounted(async () => {
  try {
    if (isManager.value) terms.value = (await http.get('/base-data/terms')).data
@@ -814,9 +884,12 @@ onMounted(async () => {
            </template>
          </el-table-column>
          <el-table-column label="学分" width="75" prop="credits" />
-          <el-table-column label="名单 / 容量" width="125">
+          <el-table-column label="名单 / 容量" width="145">
            <template #default="{ row }">
              <b class="capacity-number">{{ row.enrolledCount }} / {{ row.capacity }}</b>
+              <small v-if="row.waitlistedCount" class="waitlist-count">
+                候补 {{ row.waitlistedCount }} 人
+              </small>
            </template>
          </el-table-column>
          <el-table-column label="操作" width="190" fixed="right">
@@ -962,6 +1035,7 @@ onMounted(async () => {
              :options="[
                { label: '全部', value: 'All' },
                { label: '可选', value: 'Selectable' },
+                { label: '候补', value: 'Waitlisted' },
                { label: '已选', value: 'Selected' },
                { label: '受限', value: 'Blocked' },
              ]"
@@ -977,8 +1051,10 @@ onMounted(async () => {
            'offering-ticket',
            {
              selected: offering.enrollmentStatus === 'Enrolled',
+              waitlisted: offering.enrollmentStatus === 'Waitlisted',
              previewing: offering.id === previewOfferingId,
-              blocked: offering.enrollmentStatus !== 'Enrolled' && offeringBlockReason(offering),
+              blocked: !['Enrolled', 'Waitlisted'].includes(offering.enrollmentStatus)
+                && offeringEligibilityReason(offering),
            },
          ]"
        >
@@ -994,19 +1070,24 @@ onMounted(async () => {
            <i v-if="offering.enrollmentStatus === 'Enrolled'" class="selected-mark">
              <el-icon><CircleCheck /></el-icon> 已选
            </i>
+            <el-tag
+              v-else-if="offering.enrollmentStatus === 'Waitlisted'"
+              type="warning"
+              effect="dark"
+            >候补第 {{ offering.waitlistPosition }} 位</el-tag>
          </header>
          <div class="ticket-schedules">
-            <div v-for="schedule in offering.schedules" :key="formatSchedule(schedule)">
+            <div v-for="schedule in (offering.schedules ?? [])" :key="formatSchedule(schedule)">
              <el-icon><Tickets /></el-icon>
              <span>{{ formatSchedule(schedule) }}</span>
            </div>
            <span v-if="offering.isFlexible" class="schedule-missing">
              非排时课程 · 不占正常时间与场地
            </span>
-            <span v-else-if="!offering.schedules.length" class="schedule-missing">课表尚未发布</span>
+            <span v-else-if="!(offering.schedules ?? []).length" class="schedule-missing">课表尚未发布</span>
          </div>
          <div
-            v-if="offering.enrollmentStatus !== 'Enrolled' && offeringBlockReason(offering)"
+            v-if="!['Enrolled', 'Waitlisted'].includes(offering.enrollmentStatus) && offeringBlockReason(offering)"
            class="selection-block-reason"
          >
            {{ offeringBlockReason(offering) }}
@@ -1021,9 +1102,12 @@ onMounted(async () => {
                <span>剩余 {{ Math.max(0, offering.capacity - offering.enrolledCount) }} / {{ offering.capacity }} 席</span>
                <div><i :style="{ width: `${Math.min(100, offering.enrolledCount / offering.capacity * 100)}%` }" /></div>
              </template>
+              <small v-if="offering.waitlistedCount">
+                当前候补 {{ offering.waitlistedCount }} 人
+              </small>
            </div>
            <el-button
-              v-if="offering.schedules.length || offering.isFlexible"
+              v-if="(offering.schedules ?? []).length || offering.isFlexible"
              text
              :type="offering.id === previewOfferingId ? 'warning' : 'primary'"
              @click="togglePreview(offering)"
@@ -1035,10 +1119,22 @@ onMounted(async () => {
              :disabled="selectedRound.status !== 'Open'"
              @click="withdraw(offering)"
            >退选</el-button>
+            <el-button
+              v-else-if="offering.enrollmentStatus === 'Waitlisted'"
+              type="warning"
+              plain
+              :disabled="selectedRound.status !== 'Open'"
+              @click="cancelWaitlist(offering)"
+            >取消候补</el-button>
+            <el-button
+              v-else-if="isOfferingFull(offering) && !offeringEligibilityReason(offering)"
+              type="warning"
+              @click="joinWaitlist(offering)"
+            >加入候补</el-button>
            <el-button
              v-else
              type="primary"
-              :disabled="Boolean(offeringBlockReason(offering))"
+              :disabled="Boolean(offeringEligibilityReason(offering))"
              @click="enroll(offering)"
            >{{ offering.enrollmentStatus === 'Withdrawn' ? '重新选择' : '选择课程' }}</el-button>
          </footer>
@@ -1144,7 +1240,10 @@ onMounted(async () => {
          <div>
            <span>{{ roster.courseCode }} · {{ roster.taskNumber }}</span>
            <b>{{ roster.taskName }}</b>
-            <small>{{ roster.enrolledCount }} / {{ roster.capacity }} 人</small>
+            <small>
+              正式 {{ roster.enrolledCount }} / {{ roster.capacity }} 人
+              <template v-if="roster.waitlistedCount"> · 候补 {{ roster.waitlistedCount }} 人</template>
+            </small>
          </div>
          <div class="roster-actions">
            <el-button
@@ -1190,6 +1289,35 @@ onMounted(async () => {
          </el-table-column>
          <template #empty><el-empty description="暂无学生选课" /></template>
        </el-table>
+        <section class="waitlist-panel">
+          <div class="waitlist-panel-head">
+            <div>
+              <span>WAITLIST</span>
+              <b>候补队列</b>
+            </div>
+            <small>退课释放名额后，系统按顺位重新校验并自动递补</small>
+          </div>
+          <el-table :data="roster.waitlist">
+            <el-table-column prop="position" label="顺位" width="70" />
+            <el-table-column prop="studentNumber" label="学号" width="130" />
+            <el-table-column prop="name" label="姓名" width="90" />
+            <el-table-column prop="className" label="行政班" min-width="150" />
+            <el-table-column label="候补时间" min-width="130">
+              <template #default="{ row }">{{ formatDateTime(row.waitlistedAt) }}</template>
+            </el-table-column>
+            <el-table-column
+              v-if="roster.canManageWaitlist"
+              label="操作"
+              width="80"
+              fixed="right"
+            >
+              <template #default="{ row }">
+                <el-button link type="danger" @click="removeFromWaitlist(row)">移出</el-button>
+              </template>
+            </el-table-column>
+            <template #empty><el-empty description="暂无候补学生" /></template>
+          </el-table>
+        </section>
      </template>
    </el-drawer>

@@ -1313,4 +1441,24 @@ onMounted(async () => {
 <style scoped>
 .roster-actions { display: flex; gap: 8px; }
 .force-notice { margin-top: 8px; }
+.waitlist-count { display: block; margin-top: 3px; color: #b7791f; }
+.offering-ticket.waitlisted { border-color: #e6a23c; box-shadow: 0 10px 28px rgb(230 162 60 / 10%); }
+.seat-meter > small { display: block; margin-top: 5px; color: #b7791f; }
+.waitlist-panel { margin-top: 22px; padding-top: 18px; border-top: 1px solid var(--line); }
+.waitlist-panel-head {
+  display: flex;
+  align-items: end;
+  justify-content: space-between;
+  gap: 16px;
+  margin-bottom: 12px;
+}
+.waitlist-panel-head div { display: grid; gap: 3px; }
+.waitlist-panel-head span { color: #b7791f; font: 700 9px/1 Consolas, monospace; letter-spacing: .16em; }
+.waitlist-panel-head b { font-size: 17px; }
+.waitlist-panel-head small { color: var(--muted); text-align: right; }
+
+@media (max-width: 640px) {
+  .waitlist-panel-head { align-items: start; flex-direction: column; }
+  .waitlist-panel-head small { text-align: left; }
+}
 </style>