选课

src/Jiaowu.Api/Controllers/CourseSelectionsController.cs

@@ -337,12 +337,13 @@ public sealed class CourseSelectionsController(
     }
 
     [HttpGet("offerings/{id:guid}/eligible-students")]
-    [Authorize(Roles = RoundManagers)]
+    [Authorize(Roles = OfferingManagers)]
     public async Task<ActionResult> GetEligibleStudents(
         Guid id,
         string? keyword = null,
         int page = 1,
         int pageSize = 20,
+        bool forceMode = false,
         CancellationToken cancellationToken = default)
     {
         page = Math.Max(1, page);
@@ -360,10 +361,10 @@ public sealed class CourseSelectionsController(
             })
             .FirstOrDefaultAsync(cancellationToken);
         if (offering is null) return NotFound();
-        if (!CourseSelectionRules.SupportsProxyEnrollment(offering.CourseNature))
+        if (!forceMode && !CourseSelectionRules.SupportsProxyEnrollment(offering.CourseNature))
             return ConflictProblem("管理员代选仅适用于公共必修课。");
         if (offering.RoundStatus == CourseSelectionRoundStatus.Draft)
-            return ConflictProblem("选课批次开放后才能办理管理员代选。");
+            return ConflictProblem("选课批次开放后才能办理。");
 
         var source = db.Students.AsNoTracking()
             .Where(x =>
@@ -567,6 +568,88 @@ public sealed class CourseSelectionsController(
         return Ok(new { EnrolledCount = students.Count });
     }
 
+    [HttpPost("offerings/{offeringId:guid}/force-enroll")]
+    [Authorize(Roles = OfferingManagers)]
+    public async Task<ActionResult> ForceEnroll(
+        Guid offeringId,
+        ForceEnrollmentRequest request,
+        CancellationToken cancellationToken)
+    {
+        var studentIds = request.StudentIds.Distinct().ToArray();
+        if (studentIds.Length == 0)
+            return ValidationProblem("请至少选择一名学生。");
+        if (studentIds.Length > 100)
+            return ValidationProblem("单次最多可为 100 名学生强制选课。");
+
+        await using var transaction = await db.Database.BeginTransactionAsync(
+            IsolationLevel.Serializable, cancellationToken);
+        var offering = await db.CourseSelectionOfferings
+            .Include(x => x.CourseSelectionRound)
+            .Include(x => x.TeachingTask)
+            .ThenInclude(x => x!.Course)
+            .FirstOrDefaultAsync(x => x.Id == offeringId, cancellationToken);
+        if (offering is null) return NotFound();
+        var round = offering.CourseSelectionRound!;
+        var task = offering.TeachingTask!;
+
+        if (round.Status == CourseSelectionRoundStatus.Draft)
+            return ConflictProblem("选课批次开放后才能办理强制选课。");
+        if (task.Status != TeachingTaskStatus.Published)
+            return ConflictProblem("该教学班当前不可选。");
+
+        var students = await db.Students
+            .Include(x => x.AdministrativeClass)
+            .Where(x => studentIds.Contains(x.Id))
+            .OrderBy(x => x.StudentNumber)
+            .ToListAsync(cancellationToken);
+        if (students.Count != studentIds.Length)
+            return ValidationProblem("存在无效的学生档案。");
+
+        var existingEnrollments = await db.CourseEnrollments
+            .Where(x =>
+                x.CourseSelectionOfferingId == offeringId &&
+                studentIds.Contains(x.StudentId))
+            .ToListAsync(cancellationToken);
+        var alreadyEnrolled = existingEnrollments
+            .FirstOrDefault(x => x.Status == CourseEnrollmentStatus.Enrolled);
+        if (alreadyEnrolled is not null)
+        {
+            var dup = students.First(x => x.Id == alreadyEnrolled.StudentId);
+            return ConflictProblem(
+                $"学生 {dup.StudentNumber} {dup.Name} 已在该教学班名单中。");
+        }
+
+        var now = DateTime.UtcNow;
+        var enrolled = 0;
+        foreach (var student in students)
+        {
+            var enrollment = existingEnrollments
+                .FirstOrDefault(x => x.StudentId == student.Id);
+            if (enrollment is null)
+            {
+                db.CourseEnrollments.Add(new CourseEnrollment
+                {
+                    CourseSelectionOfferingId = offeringId,
+                    StudentId = student.Id,
+                    EnrollmentType = EnrollmentType.Retake,
+                    EnrolledAt = now
+                });
+            }
+            else
+            {
+                enrollment.Status = CourseEnrollmentStatus.Enrolled;
+                enrollment.EnrolledAt = now;
+                enrollment.WithdrawnAt = null;
+                enrollment.EnrollmentType = EnrollmentType.Retake;
+            }
+            enrolled++;
+        }
+
+        await db.SaveChangesAsync(cancellationToken);
+        await transaction.CommitAsync(cancellationToken);
+        return Ok(new { EnrolledCount = enrolled });
+    }
+
     [HttpDelete("offerings/{offeringId:guid}/admin-enrollments/{enrollmentId:guid}")]
     [Authorize(Roles = RoundManagers)]
     public async Task<ActionResult> AdminWithdraw(
@@ -638,6 +721,12 @@ public sealed class CourseSelectionsController(
                      .Select(item => (CourseEnrollmentStatus?)item.Status)
                      .FirstOrDefault(),
                  x.TeachingTask.SchedulingMode == TeachingTaskSchedulingMode.Flexible,
+                 db.CourseEnrollments.Any(e =>
+                     e.StudentId == student.Id &&
+                     e.CourseSelectionOffering!.TeachingTask!.CourseId ==
+                         x.TeachingTask.CourseId &&
+                     e.CourseSelectionOffering.CourseSelectionRound!.AcademicTermId !=
+                         round.AcademicTermId),
                  db.ScheduleEntries
                     .Where(entry =>
                         entry.TeachingTaskId == x.TeachingTaskId &&
@@ -716,6 +805,7 @@ public sealed class CourseSelectionsController(
                     .OrderByDescending(item => item.IsPrimary)
                     .Select(item => item.Teacher!.Name),
                 x.Status,
+                x.EnrollmentType,
                 x.EnrolledAt,
                 x.WithdrawnAt,
                 CanWithdraw =
@@ -762,6 +852,15 @@ public sealed class CourseSelectionsController(
                 x.AdministrativeClassId == student.AdministrativeClassId))
             return Forbid();
 
+        // Detect retake: student previously took the same course in any term
+        var isRetake = await db.CourseEnrollments.AnyAsync(
+            x =>
+                x.StudentId == student.Id &&
+                x.CourseSelectionOffering!.TeachingTask!.CourseId == task.CourseId &&
+                x.CourseSelectionOffering.CourseSelectionRound!.AcademicTermId !=
+                    round.AcademicTermId,
+            cancellationToken);
+
         var existing = await db.CourseEnrollments.FirstOrDefaultAsync(
             x =>
                 x.CourseSelectionOfferingId == offering.Id &&
@@ -769,25 +868,34 @@ public sealed class CourseSelectionsController(
             cancellationToken);
         if (existing?.Status == CourseEnrollmentStatus.Enrolled)
             return ConflictProblem("你已经选择了该教学班。");
+
         var enrolledCount = await db.CourseEnrollments.CountAsync(
             x =>
                 x.CourseSelectionOfferingId == offering.Id &&
                 x.Status == CourseEnrollmentStatus.Enrolled,
             cancellationToken);
-        if (enrolledCount >= offering.Capacity)
+        var effectiveCapacity = isRetake
+            ? CourseSelectionRules.RetakeCapacity(offering.Capacity)
+            : offering.Capacity;
+        if (enrolledCount >= effectiveCapacity)
             return ConflictProblem("该教学班名额已满。");
 
-        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 ConflictProblem("同一学期不能重复选择相同课程。");
+        // Normal enrollment: no duplicate course in same term
+        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 ConflictProblem("同一学期不能重复选择相同课程。");
+        }
 
+        // Credit limit check
         var selectedCredits = await db.CourseEnrollments
             .Where(x =>
                 x.StudentId == student.Id &&
@@ -799,16 +907,17 @@ public sealed class CourseSelectionsController(
         if (selectedCredits + task.Course!.Credits > round.MaxCredits)
         {
             return ConflictProblem(
-                $"选课后将达到 {selectedCredits + task.Course.Credits:0.#} 学分，超过本轮 {round.MaxCredits:0.#} 学分上限。");
+                $"选课后将达到 {selectedCredits + task.Course.Credits:0.#} 学分，" +
+                $"超过本轮 {round.MaxCredits:0.#} 学分上限。");
         }
 
+        // Schedule conflict check
         var candidateEntries = await PublishedScheduleEntries(
-            round.AcademicTermId,
-            [task.Id],
-            cancellationToken);
+            round.AcademicTermId, [task.Id], cancellationToken);
         if (CourseSelectionRules.RequiresPublishedSchedule(task.SchedulingMode) &&
             candidateEntries.Count == 0)
-             return ConflictProblem("该教学班尚未发布课表，暂时不能选课。");
+            return ConflictProblem("该教学班尚未发布课表，暂时不能选课。");
+
         var selectedTaskIds = await db.CourseEnrollments
             .Where(x =>
                 x.StudentId == student.Id &&
@@ -819,18 +928,28 @@ public sealed class CourseSelectionsController(
             .Distinct()
             .ToArrayAsync(cancellationToken);
         var selectedEntries = await PublishedScheduleEntries(
-            round.AcademicTermId,
-            selectedTaskIds,
-            cancellationToken);
+            round.AcademicTermId, selectedTaskIds, cancellationToken);
+
         if (CourseSelectionRules.HasScheduleConflict(candidateEntries, selectedEntries))
-            return ConflictProblem("该教学班与已选课程的上课时间冲突。");
+        {
+            if (!isRetake)
+                return ConflictProblem("该教学班与已选课程的上课时间冲突。");
+
+            // Retake: allow ≤50% overlap
+            var overlap = CourseSelectionRules.CalculateScheduleOverlap(
+                candidateEntries, selectedEntries);
+            if (overlap > 50)
+                return ConflictProblem(
+                    $"重修课程时间冲突 {overlap:F0}%，超过 50% 上限，无法选课。");
+        }
 
         if (existing is null)
         {
             existing = new CourseEnrollment
             {
                 CourseSelectionOfferingId = offering.Id,
-                StudentId = student.Id
+                StudentId = student.Id,
+                EnrollmentType = isRetake ? EnrollmentType.Retake : EnrollmentType.Normal
             };
             db.CourseEnrollments.Add(existing);
         }
@@ -839,10 +958,11 @@ public sealed class CourseSelectionsController(
             existing.Status = CourseEnrollmentStatus.Enrolled;
             existing.EnrolledAt = now;
             existing.WithdrawnAt = null;
+            existing.EnrollmentType = isRetake ? EnrollmentType.Retake : EnrollmentType.Normal;
         }
         await db.SaveChangesAsync(cancellationToken);
         await transaction.CommitAsync(cancellationToken);
-        return Created(string.Empty, new { existing.Id });
+        return Created(string.Empty, new { existing.Id, IsRetake = isRetake });
     }
 
     [HttpDelete("student/enrollments/{id:guid}")]
@@ -1096,6 +1216,9 @@ public sealed record StudentEnrollmentRequest(Guid OfferingId);
 public sealed record AdminEnrollmentRequest(
     [MinLength(1)] IReadOnlyCollection<Guid> StudentIds);
 
+public sealed record ForceEnrollmentRequest(
+    [MinLength(1)] IReadOnlyCollection<Guid> StudentIds);
+
 public sealed record StudentOfferingDto(
     Guid Id,
     Guid TeachingTaskId,
@@ -1109,6 +1232,7 @@ public sealed record StudentOfferingDto(
      bool IsOpenToAll,
      CourseEnrollmentStatus? EnrollmentStatus,
      bool IsFlexible,
+     bool IsRetake,
      IEnumerable<StudentScheduleDto> Schedules);
 
 public sealed record StudentScheduleDto(

src/Jiaowu.Api/Domain/Academic/CourseSelectionEntities.cs

@@ -36,6 +36,7 @@ public sealed class CourseEnrollment : EntityBase
     public Guid StudentId { get; set; }
     public Student? Student { get; set; }
     public CourseEnrollmentStatus Status { get; set; } = CourseEnrollmentStatus.Enrolled;
+    public EnrollmentType EnrollmentType { get; set; } = EnrollmentType.Normal;
     public DateTime EnrolledAt { get; set; } = DateTime.UtcNow;
     public DateTime? WithdrawnAt { get; set; }
 }
@@ -52,3 +53,9 @@ public enum CourseEnrollmentStatus
     Enrolled = 1,
     Withdrawn = 2
 }
+
+public enum EnrollmentType
+{
+    Normal = 1,
+    Retake = 2
+}

src/Jiaowu.Api/Infrastructure/CourseSelection/CourseSelectionRules.cs

@@ -26,4 +26,46 @@ public static class CourseSelectionRules
         candidateEntries.Any(candidate =>
             selectedEntries.Any(selected =>
                 ScheduleConflictDetector.TimeOverlaps(candidate, selected)));
+
+    /// <summary>
+    /// Returns the overlap percentage of candidate schedule entries with selected entries.
+    /// 0 = no conflict, 100 = fully overlapping.
+    /// Used for retake enrollment where ≤50% overlap is allowed.
+    /// </summary>
+    public static double CalculateScheduleOverlap(
+        IReadOnlyCollection<ScheduleEntry> candidateEntries,
+        IReadOnlyCollection<ScheduleEntry> selectedEntries)
+    {
+        if (candidateEntries.Count == 0 || selectedEntries.Count == 0)
+            return 0;
+
+        int totalCandidatePeriods = 0;
+        int overlappedPeriods = 0;
+
+        foreach (var candidate in candidateEntries)
+        {
+            totalCandidatePeriods += candidate.PeriodCount;
+            foreach (var selected in selectedEntries)
+            {
+                if (!ScheduleConflictDetector.TimeOverlaps(candidate, selected))
+                    continue;
+                // Calculate overlapping periods
+                var overlapStart = Math.Max(
+                    candidate.StartPeriod, selected.StartPeriod);
+                var overlapEnd = Math.Min(
+                    candidate.StartPeriod + candidate.PeriodCount,
+                    selected.StartPeriod + selected.PeriodCount);
+                if (overlapEnd > overlapStart)
+                    overlappedPeriods += overlapEnd - overlapStart;
+            }
+        }
+
+        return totalCandidatePeriods == 0
+            ? 0
+            : (double)overlappedPeriods / totalCandidatePeriods * 100;
+    }
+
+    /// <summary>Retake expanded capacity: ceiling(original * 1.15).</summary>
+    public static int RetakeCapacity(int originalCapacity) =>
+        (int)Math.Ceiling(originalCapacity * 1.15);
 }

src/Jiaowu.Api/Infrastructure/Persistence/DevelopmentSqliteMigrator.cs

@@ -34,6 +34,8 @@ public sealed class DevelopmentSqliteMigrator(
         "20260725_19_flexible_grades";
     private const string ExamSchedulingOptimizationMigration =
         "20260725_20_exam_scheduling_optimization";
+    private const string RetakeEnrollmentMigration =
+        "20260725_21_retake_enrollment";
 
     public async Task MigrateAsync(CancellationToken cancellationToken = default)
     {
@@ -225,6 +227,19 @@ public sealed class DevelopmentSqliteMigrator(
                 ? []
                 : ExamSchedulingOptimizationStatements,
             cancellationToken);
+
+        var retakeEnrollmentExists = await db.Database
+            .SqlQueryRaw<int>(
+                """
+                SELECT COUNT(*) AS "Value"
+                FROM pragma_table_info('CourseEnrollments')
+                WHERE name = 'EnrollmentType'
+                """)
+            .AnyAsync(value => value > 0, cancellationToken);
+        await ApplyMigrationAsync(
+            RetakeEnrollmentMigration,
+            retakeEnrollmentExists ? [] : RetakeEnrollmentStatements,
+            cancellationToken);
     }
 
     private async Task ApplyMigrationAsync(
@@ -1461,4 +1476,12 @@ public sealed class DevelopmentSqliteMigrator(
             ON "ExamSessions" ("RequiredBuildingId");
         """
     ];
+
+    private static readonly string[] RetakeEnrollmentStatements =
+    [
+        """
+        ALTER TABLE "CourseEnrollments"
+        ADD COLUMN "EnrollmentType" INTEGER NOT NULL DEFAULT 1;
+        """
+    ];
 }

src/Jiaowu.Api/Infrastructure/Persistence/Migrations/MySql/20260725150000_RetakeEnrollment.cs

@@ -0,0 +1,29 @@
+using Microsoft.EntityFrameworkCore.Migrations;
+
+#nullable disable
+
+namespace Jiaowu.Api.Infrastructure.Persistence.Migrations.MySql
+{
+    /// <inheritdoc />
+    public partial class RetakeEnrollment : Migration
+    {
+        /// <inheritdoc />
+        protected override void Up(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.AddColumn<int>(
+                name: "EnrollmentType",
+                table: "CourseEnrollments",
+                type: "int",
+                nullable: false,
+                defaultValue: 1);
+        }
+
+        /// <inheritdoc />
+        protected override void Down(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.DropColumn(
+                name: "EnrollmentType",
+                table: "CourseEnrollments");
+        }
+    }
+}