修复实验成绩评分方案保存的外键失败

src/Jiaowu.Api/Controllers/ExperimentGradesController.cs

@@ -568,21 +568,39 @@ public sealed class ExperimentGradesController(
 
         sheet.ContributionWeight = request.ContributionWeight;
         sheet.PassScore = request.PassScore;
-        db.ExperimentGradeItems.RemoveRange(sheet.Items);
+        var existingItems = sheet.Items.ToList();
+        var existingItemScores = sheet.Records
+            .SelectMany(record => record.ItemScores)
+            .ToList();
+
+        // MySQL must see each replacement item before its score rows.  Do not
+        // rely on a single mixed insert/delete batch to infer that order.
+        await using var transaction =
+            await db.Database.BeginTransactionAsync(cancellationToken);
+        db.ExperimentGradeItemScores.RemoveRange(existingItemScores);
+        db.ExperimentGradeItems.RemoveRange(existingItems);
         foreach (var record in sheet.Records)
         {
-            record.ItemScores.Clear();
             record.TotalScore = null;
             record.IsPassed = null;
         }
-        sheet.Items = replacementItems;
-        foreach (var record in sheet.Records)
-            foreach (var item in replacementItems)
-                record.ItemScores.Add(new ExperimentGradeItemScore
-                {
-                    ExperimentGradeItemId = item.Id
-                });
+
         await db.SaveChangesAsync(cancellationToken);
+
+        foreach (var item in replacementItems)
+            item.ExperimentGradeSheetId = sheet.Id;
+        db.ExperimentGradeItems.AddRange(replacementItems);
+        await db.SaveChangesAsync(cancellationToken);
+
+        db.ExperimentGradeItemScores.AddRange(
+            sheet.Records.SelectMany(record => replacementItems.Select(item =>
+                new ExperimentGradeItemScore
+                {
+                    ExperimentGradeRecordId = record.Id,
+                    ExperimentGradeItemId = item.Id
+                })));
+        await db.SaveChangesAsync(cancellationToken);
+        await transaction.CommitAsync(cancellationToken);
         return NoContent();
     }