修复MySQL问题

src/Jiaowu.Api/Infrastructure/Exams/ExamArrangementService.cs

@@ -230,12 +230,14 @@ public sealed class ExamArrangementService(AppDbContext db)
         foreach (var id in dbBusyIds) busyTeacherIds.Add(id);
         foreach (var id in excludeTeacherIds) busyTeacherIds.Add(id);
 
-        return await db.Teachers.AsNoTracking()
-            .Where(x => x.Status == TeacherStatus.Active)
-            .WhereNotIn(busyTeacherIds, x => x.Id)
-            .OrderBy(x => Guid.NewGuid())
-            .Take(needed)
+        var candidates = await InvigilatorCandidateQuery
+            .Create(db, busyTeacherIds)
             .ToListAsync(cancellationToken);
+
+        return candidates
+            .OrderBy(_ => Random.Shared.Next())
+            .Take(needed)
+            .ToList();
     }
 }
 

src/Jiaowu.Api/Infrastructure/Exams/InvigilatorCandidateQuery.cs

@@ -0,0 +1,15 @@
+using Jiaowu.Api.Domain.Academic;
+using Jiaowu.Api.Infrastructure.Persistence;
+using Microsoft.EntityFrameworkCore;
+
+namespace Jiaowu.Api.Infrastructure.Exams;
+
+internal static class InvigilatorCandidateQuery
+{
+    public static IQueryable<Teacher> Create(
+        AppDbContext db,
+        IEnumerable<Guid> excludedTeacherIds) =>
+        db.Teachers.AsNoTracking()
+            .Where(x => x.Status == TeacherStatus.Active)
+            .WhereNotIn(excludedTeacherIds, x => x.Id);
+}

src/Jiaowu.Api/Infrastructure/Exams/MakeupExamArrangementService.cs

@@ -225,11 +225,13 @@ public sealed class MakeupExamArrangementService(AppDbContext db)
         foreach (var id in dbBusyIds) busyTeacherIds.Add(id);
         foreach (var id in excludeTeacherIds) busyTeacherIds.Add(id);
 
-        return await db.Teachers.AsNoTracking()
-            .Where(x => x.Status == TeacherStatus.Active)
-            .WhereNotIn(busyTeacherIds, x => x.Id)
-            .OrderBy(x => Guid.NewGuid())
-            .Take(needed)
+        var candidates = await InvigilatorCandidateQuery
+            .Create(db, busyTeacherIds)
             .ToListAsync(cancellationToken);
+
+        return candidates
+            .OrderBy(_ => Random.Shared.Next())
+            .Take(needed)
+            .ToList();
     }
 }