自选项目实验优化

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

@@ -51,6 +51,8 @@ public sealed class AppDbContext(DbContextOptions<AppDbContext> options)
         Set<ClassroomReservation>();
     public DbSet<ExperimentProject> ExperimentProjects => Set<ExperimentProject>();
     public DbSet<ExperimentSession> ExperimentSessions => Set<ExperimentSession>();
+    public DbSet<ExperimentSessionInstructor> ExperimentSessionInstructors =>
+        Set<ExperimentSessionInstructor>();
     public DbSet<ExperimentBooking> ExperimentBookings => Set<ExperimentBooking>();
     public DbSet<ExperimentGradeSheet> ExperimentGradeSheets =>
         Set<ExperimentGradeSheet>();
@@ -690,6 +692,8 @@ public sealed class AppDbContext(DbContextOptions<AppDbContext> options)
             entity.Property(x => x.Name).HasMaxLength(120);
             entity.Property(x => x.Description).HasMaxLength(1000);
             entity.Property(x => x.Requirements).HasMaxLength(1000);
+            entity.Property(x => x.SelectionStartsAt).HasConversion<UtcDateTimeConverter>();
+            entity.Property(x => x.SelectionEndsAt).HasConversion<UtcDateTimeConverter>();
             // 集中安排会为同一教学任务的每一条实验课表记录生成项目；
             // 自行安排仍由控制器保持“教学任务 + 编码”唯一。
             entity.HasIndex(x => new
@@ -805,6 +809,19 @@ public sealed class AppDbContext(DbContextOptions<AppDbContext> options)
                 .OnDelete(DeleteBehavior.Restrict);
         });
 
+        builder.Entity<ExperimentSessionInstructor>(entity =>
+        {
+            entity.HasIndex(x => new { x.ExperimentSessionId, x.TeacherId })
+                .IsUnique();
+            entity.HasIndex(x => x.TeacherId);
+            entity.HasOne(x => x.ExperimentSession).WithMany(x => x.Instructors)
+                .HasForeignKey(x => x.ExperimentSessionId)
+                .OnDelete(DeleteBehavior.Cascade);
+            entity.HasOne(x => x.Teacher).WithMany()
+                .HasForeignKey(x => x.TeacherId)
+                .OnDelete(DeleteBehavior.Restrict);
+        });
+
         builder.Entity<ExperimentCourseGrade>(entity =>
         {
             entity.Property(x => x.WeightedAverageScore).HasPrecision(5, 1);