c# – 如何删除级联底部的实体 – > EF中的非级联删除链？
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对不起,完全无益的标题……我无法将这个问题变成更好的话.
我有以下实体,每个实体都由Id属性标识： >底盘 当我使用POCO时,这些实体并没有什么突破性的.例如,Chassis类的定义如下： public class Chassis
{
public int Id { get; set; }
// Other properties omitted for brevity.
public ICollection<Slot> Slots { get; set; }
public Chassis()
{
Slots = new Collection<Slot>();
}
}
关系如下： >机箱有许多插槽(CASCADE). 因此,删除机箱时,将删除所有插槽.精细.但是,我还要删除这些插槽中安装的所有卡.不行我正在尝试将一些代码挂钩到OnSavingChanges事件(我在SaveChanges()之前触发),这样当机箱被标记为已删除时,我也会删除它的卡片. 首先,我试过： OnSavingChanges += (x,y) =>
{
var ctx = x as DbContext;
var chassis = ctx.ChangeTracker.Entries<Chassis>().Where(e => e.State == EntityState.Deleted);
// Delete all cards on a deleted chassis.
foreach (var c in chassis)
{
// Cannot just do c.Slots,as EF seems to empty the nav. property now the
// chassis is deleted.
var slots = ctx.Slots.Where(s => s.ChassisId == c.Entity.Id).ToList();
foreach (var s in slots)
{
if (s.Card != null)
{
ctx.Cards.Remove(s.Card);
}
}
}
};
…但是这引发了异常：
然后我尝试添加ctx.Detach(s);在我的内部foreach循环中,停止EF试图保存已经删除的通过级联Slots实体： foreach (var s in slots)
{
if (s.Card != null)
{
ctx.Cards.Remove(s.Card);
}
// Otherwise EF attempts to save the slot,which results in a exception saying the principle
// end of the relatioship Chassis_Slots has already been deleted.
ctx.Detach(s);
}
…然后EF随后发出以下例外情况：
…有点让我在岩石和坚硬的地方之间,完全出于想法. 任何人都可以建议一个更成功的方法/方法来做到这一点？ 解决方法
这是序列.
>删除机箱后,由于删除级联机制,所有插槽也将被删除.简单吧？ 要解决此问题,您需要引入新的事务/上下文. public override int SaveChanges()
{
var deletedCardIds = new List<int>();
var chassises = ChangeTracker.Entries<Chassis>().Where(e => e.State == EntityState.Deleted);
foreach (var chassis in chassises)
{
var slots = Slots.Where(s => s.ChassisId == chassis.Entity.Id).ToArray();
foreach (var slot in slots)
{
if (slot.CardId.HasValue && !deletedCardIds.Contains(slot.CardId.Value))
{
deletedCardIds.Add(slot.CardId.Value);
}
}
}
// Commits original transaction.
var originalRowsAffected = base.SaveChanges();
int additionalRowsAffected = 0;
if (deletedCardIds.Count > 0)
{
// Opens new transaction.
using (var newContext = new AppContext())
{
foreach (var cardId in deletedCardIds)
{
var deletedCard = newContext.Cards.Find(cardId);
if (deletedCard != null)
{
newContext.Cards.Remove(deletedCard);
}
}
// Commits new transaction.
additionalRowsAffected = newContext.SaveChanges();
}
}
return originalRowsAffected + additionalRowsAffected;
}
PS >您有两个独立的事务,可能会导致意外行为(atomicity无法保证). UPDATE 今天我才意识到我们可以简单地使用TransactionScope到commit several operations in a single transaction.就像在数据库中执行此代码一样. begin tran delete from dbo.Chassis delete from dbo.Cards commit tran 如果您使用EF6以上,您可以使用Database.BeginTransaction否则使用TransactionScope. public override int SaveChanges()
{
var deletedCardIds = new List<int>();
var chassises = ChangeTracker.Entries<Chassis>().Where(e => e.State == EntityState.Deleted);
foreach (var chassis in chassises)
{
var cardIds = Slots.Where(s => s.ChassisId == chassis.Entity.Id)
.Where(s => s.CardId.HasValue)
.Select(s => s.CardId.Value)
.ToArray();
deletedCardIds.AddRange(cardIds);
}
int originalRowsAffected;
int additionalRowsAffected;
using (var transaction = new TransactionScope())
{
originalRowsAffected = base.SaveChanges();
deletedCardIds.Distinct().ToList()
.ForEach(id => Entry(new Card { Id = id }).State = EntityState.Deleted);
additionalRowsAffected = base.SaveChanges();
transaction.Complete();
}
return originalRowsAffected + additionalRowsAffected;
}
通过在上面更新的代码中引入事务,SaveChanges既可以全部发生,也不会发生任何事情,现在保证原子性. （编辑：李大同） 【声明】本站内容均来自网络，其相关言论仅代表作者个人观点，不代表本站立场。若无意侵犯到您的权利，请及时与联系站长删除相关内容! |