Question

我一直在尝试向DbSet添加多个对象，但是我尝试的所有内容都会导致'System.InvalidOperationException：Collection被修改;枚举操作可能无法执行。堆栈跟踪：

在System.ThrowHelper.ThrowInvalidOperationException（ExceptionResource资源）在System.Collections.Generic.List 1.Enumerator.MoveNextRare() at System.Collections.Generic.List 1.Enumerator.MoveNext（）在System.Data.Entity.Core.Objects.EntityEntry.TakeSnapshotOfRelationships（）在System.Data.Entity.Core.Objects.Internal.EntityWrapperWithoutRelationships 1.TakeSnapshotOfRelationships(EntityEntry entry) at System.Data.Entity.Core.Objects.ObjectContext.AddSingleObject(EntitySet entitySet, IEntityWrapper wrappedEntity, String argumentName) at System.Data.Entity.Core.Objects.ObjectContext.AddObject(String entitySetName, Object entity) at System.Data.Entity.Internal.Linq.InternalSet 1.＆lt;＆gt; c__DisplayClassd.b__c（） at System.Data.Entity.Internal.Linq.InternalSet 1.ActOnSet(Action action, EntityState newState, Object entity, String methodName) at System.Data.Entity.Internal.Linq.InternalSet 1.Add（Object entity）在System.Data.Entity.DbSet`1.Add（TEntity entity）

这只会在第二次将“Mail”对象添加到上下文时出现代码：

            foreach (var folderId in folderIds)
            {
                db.Mails.Add(new Mail
                {
                    From = from,
                    To = to,
                    CC = cc,
                    Attachments = attachments,
                    BodyHtml = bodyHtml,
                    BodyPlain = bodyPlain,
                    Subject = subject,
                    Incoming = true,
                    Priority = receivedMail.Priority,
                    ReceivedOn = DateTime.UtcNow,
                    Status = MailStatus.Open,
                    Read = false,
                    Folder = db.Folders.Find(folderId)
                });
            }

我正在进行的唯一枚举是在folderIds上，这是一个int数组，你可以在堆栈跟踪中看到它不是原因。我已经坚持了一段时间，并尝试了各种方法，如临时收集和使用AddRange或每次添加后保存上下文。

非常感谢任何有关问题所在的帮助。

Answer 1

附件还收藏？如果它来自任何db对象，则在分配时尝试调用ToList（）。

 foreach (var folderId in folderIds)
        {
            db.Mails.Add(new Mail
            {
                From = from,
                To = to,
                CC = cc,
                Attachments = attachments.ToList(),
                BodyHtml = bodyHtml,
                BodyPlain = bodyPlain,
                Subject = subject,
                Incoming = true,
                Priority = receivedMail.Priority,
                ReceivedOn = DateTime.UtcNow,
                Status = MailStatus.Open,
                Read = false,
                Folder = db.Folders.Find(folderId)
            });
        }

EF6：集合已修改，枚举操作可能无法执行

1 个答案: