C# 实体框架 .Remove() 与 .DeleteObject()

Entity Framework .Remove() vs. .DeleteObject()

提问by Sam Leach

You can remove an item from a database using EF by using the following two methods.

您可以使用以下两种方法使用 EF 从数据库中删除项目。

• EntityCollection.Remove Method

• ObjectContext.DeleteObject Method

• EntityCollection.Remove 方法

• ObjectContext.DeleteObject 方法

The first is on the EntityCollectionand the second on the ObjectContext.

第一个在 上EntityCollection，第二个在 上ObjectContext。

When should each be used?

每个应该什么时候使用？

Is one prefered over the other?

一个比另一个更受欢迎吗？

Remove()returns a booland DeleteObject()returns void.

Remove()返回 abool并DeleteObject()返回void。

采纳答案by Slauma

It's not generally correct that you can "remove an item from a database" with both methods. To be precise it is like so:

使用这两种方法都可以“从数据库中删除项目”通常是不正确的。准确来说是这样的：

• ObjectContext.DeleteObject(entity)marks the entity as Deletedin the context. (It's EntityStateis Deletedafter that.) If you call SaveChangesafterwards EF sends a SQL DELETEstatement to the database. If no referential constraints in the database are violated the entity will be deleted, otherwise an exception is thrown.

• EntityCollection.Remove(childEntity)marks the relationship between parent and childEntityas Deleted. If the childEntityitself is deleted from the database and what exactly happens when you call SaveChangesdepends on the kind of relationship between the two:

  • If the relationship is optional, i.e. the foreign key that refers from the child to the parent in the database allows NULLvalues, this foreign will be set to null and if you call SaveChangesthis NULLvalue for the childEntitywill be written to the database (i.e. the relationship between the two is removed). This happens with a SQL UPDATEstatement. No DELETEstatement occurs.

  • If the relationship is required(the FK doesn't allow NULLvalues) and the relationship is not identifying(which means that the foreign key is not part of the child's (composite) primary key) you have to either add the child to another parent or you have to explicitly delete the child (with DeleteObjectthen). If you don't do any of these a referential constraint is violated and EF will throw an exception when you call SaveChanges- the infamous "The relationship could not be changed because one or more of the foreign-key properties is non-nullable"exception or similar.

  • If the relationship is identifying(it's necessarily requiredthen because any part of the primary key cannot be NULL) EF will mark the childEntityas Deletedas well. If you call SaveChangesa SQL DELETEstatement will be sent to the database. If no other referential constraints in the database are violated the entity will be deleted, otherwise an exception is thrown.

• ObjectContext.DeleteObject(entity)将实体Deleted标记为在上下文中。（它EntityState是Deleted在那之后。）如果你在SaveChanges之后调用，EF 会向DELETE数据库发送一条 SQL语句。如果没有违反数据库中的引用约束，实体将被删除，否则抛出异常。

• EntityCollection.Remove(childEntity)标记parent 和childEntityas之间的关系Deleted。如果childEntity本身从数据库中删除，调用时究竟发生了什么SaveChanges取决于两者之间的关系类型：

  • 如果关系是可选的，即数据库中从子代到父代的外键允许NULL值，则此外键将设置为空，如果您调用SaveChanges此NULL值，childEntity则将写入数据库（即这两个被删除）。这发生在 SQLUPDATE语句中。没有DELETE语句发生。

  • 如果需要该关系（FK 不允许NULL值）并且该关系未识别（这意味着外键不是子项（复合）主键的一部分），您必须将子项添加到另一个父项或你必须明确删除孩子（DeleteObject然后）。如果您不执行其中任何一项操作，则会违反引用约束，EF 将在您调用时抛出异常SaveChanges- 臭名昭著的“关系无法更改，因为一个或多个外键属性不可为空”异常或相似的。

  • 如果关系被识别（它不一定需要然后，因为主键的任何部分不能是NULL）EF将标记childEntity作为Deleted为好。如果你调用SaveChanges一个SQLDELETE语句就会被发送到数据库中。如果没有违反数据库中的其他引用约束，实体将被删除，否则抛出异常。

I am actually a bit confused about the Remarks section on the MSDN pageyou have linked because it says: "If the relationship has a referential integrity constraint, calling the Remove method on a dependent object marks both the relationship and the dependent object for deletion.". This seems unprecise or even wrong to me because all three cases above have a "referential integrity constraint" but only in the last case the child is in fact deleted. (Unless they mean with "dependent object" an object that participates in an identifying relationship which would be an unusual terminology though.)

实际上，我对您链接的 MSDN 页面上的备注部分感到有些困惑，因为它说：“如果关系具有参照完整性约束，则在依赖对象上调用 Remove 方法会将关系和依赖对象标记为删除。”。这对我来说似乎不准确甚至是错误的，因为上述所有三种情况都有一个“参照完整性约束”，但只有在最后一种情况下，子项实际上被删除了。（除非他们的意思是“依赖对象”是参与识别关系的对象，但这将是一个不寻常的术语。）

回答by Matas Vaitkevicius

If you really want to use Deleted, you'd have to make your foreign keys nullable, but then you'd end up with orphaned records (which is one of the main reasons you shouldn't be doing that in the first place). So just use Remove()

如果你真的想使用 Deleted，你必须让你的外键可以为空，但是你最终会得到孤立的记录（这是你首先不应该这样做的主要原因之一）。所以只需使用Remove()

ObjectContext.DeleteObject(entity)marks the entity as Deleted in the context. (It's EntityState is Deleted after that.) If you call SaveChanges afterwards EF sends a SQL DELETE statement to the database. If no referential constraints in the database are violated the entity will be deleted, otherwise an exception is thrown.

ObjectContext.DeleteObject(entity)在上下文中将实体标记为已删除。（之后 EntityState 被删除。）如果您在之后调用 SaveChanges，EF 会向数据库发送 SQL DELETE 语句。如果没有违反数据库中的引用约束，实体将被删除，否则抛出异常。

EntityCollection.Remove(childEntity)marks the relationship between parent and childEntity as Deleted. If the childEntity itself is deleted from the database and what exactly happens when you call SaveChanges depends on the kind of relationship between the two:

EntityCollection.Remove(childEntity)将 parent 和 childEntity 之间的关系标记为 Deleted。如果 childEntity 本身从数据库中删除，那么调用 SaveChanges 时究竟发生了什么取决于两者之间的关系类型：

A thing worth noting is that setting .State = EntityState.Deleteddoes not trigger automatically detected change.(archive)

值得注意的是，设置.State = EntityState.Deleted不会触发自动检测到的更改。（存档）