时间

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

@@ -166,6 +166,14 @@ public sealed class AppDbContext(DbContextOptions<AppDbContext> options)
         configurationBuilder.Properties<TimeOnly>()
             .HaveConversion<TimeOnlyTimeSpanConverter>()
             .HaveColumnType("time");
+
+        // MySQL DATETIME has no offset or DateTimeKind. All system timestamps
+        // are persisted as UTC, so restore that contract when materializing
+        // them. System.Text.Json will then emit the trailing "Z", allowing
+        // browsers to convert timestamps to the viewer's local time correctly.
+        configurationBuilder.Properties<DateTime>()
+            .HaveConversion<UtcDateTimeConverter>()
+            .HaveColumnType("datetime(6)");
     }
 
     protected override void OnModelCreating(ModelBuilder builder)
@@ -1086,6 +1094,10 @@ public sealed class AppDbContext(DbContextOptions<AppDbContext> options)
         });
         builder.Entity<ExamSession>(entity =>
         {
+            // Exam slot times are China-local wall-clock times, not instants.
+            // Keep their existing API representation offset-free.
+            entity.Property(x => x.StartsAt).HasConversion<UnspecifiedDateTimeConverter>();
+            entity.Property(x => x.EndsAt).HasConversion<UnspecifiedDateTimeConverter>();
             entity.Property(x => x.Notes).HasMaxLength(500);
             entity.HasIndex(x => new { x.ExamPlanId, x.StartsAt });
             entity.HasIndex(x => x.TeachingTaskId);
@@ -1112,6 +1124,8 @@ public sealed class AppDbContext(DbContextOptions<AppDbContext> options)
         builder.Entity<ExamRoomAssignment>(entity =>
         {
             entity.ToTable("ExamRooms");
+            entity.Property(x => x.StartsAt).HasConversion<UnspecifiedDateTimeConverter>();
+            entity.Property(x => x.EndsAt).HasConversion<UnspecifiedDateTimeConverter>();
             entity.HasIndex(x => new { x.ExamPlanId, x.StartsAt })
                 .HasDatabaseName("IX_ExamRooms_Plan_Time");
             entity.HasIndex(x => new
@@ -1200,6 +1214,9 @@ public sealed class AppDbContext(DbContextOptions<AppDbContext> options)
         });
         builder.Entity<MakeupExamSession>(entity =>
         {
+            // Makeup-exam slot times follow the same wall-clock convention.
+            entity.Property(x => x.StartsAt).HasConversion<UnspecifiedDateTimeConverter>();
+            entity.Property(x => x.EndsAt).HasConversion<UnspecifiedDateTimeConverter>();
             entity.Property(x => x.Notes).HasMaxLength(500);
             entity.HasIndex(x => new { x.MakeupExamPlanId, x.StartsAt });
             entity.HasIndex(x => x.TeachingTaskId);
@@ -1646,3 +1663,15 @@ public sealed class TimeOnlyTimeSpanConverter()
     : ValueConverter<TimeOnly, TimeSpan>(
         time => time.ToTimeSpan(),
         value => TimeOnly.FromTimeSpan(value));
+
+public sealed class UtcDateTimeConverter()
+    : ValueConverter<DateTime, DateTime>(
+        value => value.Kind == DateTimeKind.Local
+            ? value.ToUniversalTime()
+            : DateTime.SpecifyKind(value, DateTimeKind.Utc),
+        value => DateTime.SpecifyKind(value, DateTimeKind.Utc));
+
+public sealed class UnspecifiedDateTimeConverter()
+    : ValueConverter<DateTime, DateTime>(
+        value => DateTime.SpecifyKind(value, DateTimeKind.Unspecified),
+        value => DateTime.SpecifyKind(value, DateTimeKind.Unspecified));