预演

src/Jiaowu.Api/Controllers/CoursesController.cs

@@ -84,6 +84,17 @@ public sealed class CoursesController(
                 x.Nature,
                 x.AssessmentMethod,
                 x.Description,
+                PrerequisiteCourseIds = x.Prerequisites
+                    .OrderBy(item => item.PrerequisiteCourse!.Code)
+                    .Select(item => item.PrerequisiteCourseId),
+                Prerequisites = x.Prerequisites
+                    .OrderBy(item => item.PrerequisiteCourse!.Code)
+                    .Select(item => new
+                    {
+                        item.PrerequisiteCourseId,
+                        item.PrerequisiteCourse!.Code,
+                        item.PrerequisiteCourse.Name
+                    }),
                 x.IsEnabled,
                 x.SortOrder,
                 x.CreatedAt,
@@ -146,9 +157,6 @@ public sealed class CoursesController(
         CourseRequest request,
         CancellationToken cancellationToken)
     {
-        var validation = await ValidateAsync(request, cancellationToken);
-        if (validation is not null) return validation;
-
         var entity = new Course
         {
             Code = request.Code.Trim(),
@@ -166,6 +174,16 @@ public sealed class CoursesController(
             IsEnabled = request.IsEnabled,
             SortOrder = request.SortOrder
         };
+        var validation = await ValidateAsync(entity.Id, request, cancellationToken);
+        if (validation is not null) return validation;
+
+        entity.Prerequisites = NormalizePrerequisiteIds(request)
+            .Select(prerequisiteId => new CoursePrerequisite
+            {
+                CourseId = entity.Id,
+                PrerequisiteCourseId = prerequisiteId
+            })
+            .ToList();
         db.Courses.Add(entity);
         return await SaveAsync(entity.Id, true, cancellationToken);
     }
@@ -177,10 +195,12 @@ public sealed class CoursesController(
         CourseRequest request,
         CancellationToken cancellationToken)
     {
-        var entity = await db.Courses.FindAsync([id], cancellationToken);
+        var entity = await db.Courses
+            .Include(x => x.Prerequisites)
+            .FirstOrDefaultAsync(x => x.Id == id, cancellationToken);
         if (entity is null) return NotFound();
         if (!CanManage(entity.CollegeId, entity.Nature)) return Forbid();
-        var validation = await ValidateAsync(request, cancellationToken);
+        var validation = await ValidateAsync(id, request, cancellationToken);
         if (validation is not null) return validation;
 
         entity.Code = request.Code.Trim();
@@ -197,6 +217,19 @@ public sealed class CoursesController(
         entity.Description = Normalize(request.Description);
         entity.IsEnabled = request.IsEnabled;
         entity.SortOrder = request.SortOrder;
+        var prerequisiteIds = NormalizePrerequisiteIds(request).ToHashSet();
+        db.CoursePrerequisites.RemoveRange(
+            entity.Prerequisites.Where(x =>
+                !prerequisiteIds.Contains(x.PrerequisiteCourseId)));
+        foreach (var prerequisiteId in prerequisiteIds.Except(
+                     entity.Prerequisites.Select(x => x.PrerequisiteCourseId)))
+        {
+            entity.Prerequisites.Add(new CoursePrerequisite
+            {
+                CourseId = entity.Id,
+                PrerequisiteCourseId = prerequisiteId
+            });
+        }
         return await SaveAsync(entity.Id, false, cancellationToken);
     }
 
@@ -212,6 +245,7 @@ public sealed class CoursesController(
     }
 
     private async Task<ActionResult?> ValidateAsync(
+        Guid courseId,
         CourseRequest request,
         CancellationToken cancellationToken)
     {
@@ -224,9 +258,62 @@ public sealed class CoursesController(
             return ValidationProblem("所选课程分类不存在或已停用。");
         if (request.LectureHours + request.PracticeHours > request.TotalHours)
             return ValidationProblem("讲授学时与实践学时之和不能超过总学时。");
+
+        var prerequisiteIds = NormalizePrerequisiteIds(request).ToArray();
+        if (prerequisiteIds.Contains(courseId))
+            return ValidationProblem("课程不能把自身设置为先修课程。");
+        var accessiblePrerequisiteCount = await ScopedCourses()
+            .CountAsync(x =>
+                prerequisiteIds.Contains(x.Id) &&
+                x.IsEnabled,
+                cancellationToken);
+        if (accessiblePrerequisiteCount != prerequisiteIds.Length)
+            return ValidationProblem("包含不存在、已停用或不在当前数据范围内的先修课程。");
+        if (await CreatesPrerequisiteCycleAsync(
+                courseId,
+                prerequisiteIds,
+                cancellationToken))
+            return ValidationProblem("先修关系不能形成循环依赖。");
         return null;
     }
 
+    private async Task<bool> CreatesPrerequisiteCycleAsync(
+        Guid courseId,
+        IReadOnlyCollection<Guid> prerequisiteIds,
+        CancellationToken cancellationToken)
+    {
+        if (prerequisiteIds.Count == 0) return false;
+
+        var edges = await db.CoursePrerequisites.AsNoTracking()
+            .Where(x => x.CourseId != courseId)
+            .Select(x => new { x.CourseId, x.PrerequisiteCourseId })
+            .ToListAsync(cancellationToken);
+        var prerequisitesByCourse = edges
+            .GroupBy(x => x.CourseId)
+            .ToDictionary(
+                group => group.Key,
+                group => group.Select(x => x.PrerequisiteCourseId).ToArray());
+
+        foreach (var prerequisiteId in prerequisiteIds)
+        {
+            var pending = new Stack<Guid>();
+            var visited = new HashSet<Guid>();
+            pending.Push(prerequisiteId);
+            while (pending.TryPop(out var candidate))
+            {
+                if (candidate == courseId) return true;
+                if (!visited.Add(candidate) ||
+                    !prerequisitesByCourse.TryGetValue(candidate, out var next))
+                    continue;
+                foreach (var item in next) pending.Push(item);
+            }
+        }
+        return false;
+    }
+
+    private static IEnumerable<Guid> NormalizePrerequisiteIds(CourseRequest request) =>
+        (request.PrerequisiteCourseIds ?? []).Distinct();
+
     private IQueryable<Course> ScopedCourses()
     {
         var scope = currentUserDataScope.Current;
@@ -307,4 +394,5 @@ public sealed record CourseRequest(
     AssessmentMethod AssessmentMethod,
     [MaxLength(1000)] string? Description,
     bool IsEnabled,
-    int SortOrder);
+    int SortOrder,
+    IReadOnlyCollection<Guid>? PrerequisiteCourseIds = null);