乐趣区

关于sql:EF-core关联对象删除

jiezi

DeleteBehavior

@想一想 @：在关联的 entity 之间，当删除父 entity（比方 Classroom）的时候，子 entity（比方 Student）应该如何解决？

温习：__SQL 中的 Cascade Delete

自定义：OnDelete() 办法

在 OnModelCreating() 中可调用 OnDelete() 办法，传递 DeleteBehavior 枚举值，指定 EF core 如何操作。

比方：

modelBuilder.Entity<Student>() .HasOne<Bed>(s => s.SleepIn) .WithOne(b => b.Owner) .HasForeignKey<Student>(s => s.SleepInId) .OnDelete(DeleteBehavior.Cascade) ;

EF 的 DeleteBehavior 枚举能够被归为 3 类。对应着当删除父 entity 的时候，子 entity 或数据行的 3 种解决计划：

  1. Cascade/ClientCascade：子 entity 被同时删除
  2. SetNull/ClientSetNull：其外键被设置为 null（如果外键不能被设置为 null，会报异样）
  3. NoAction：不产生扭转

Client 和非 Client

比方 DeleteBehavior.SetNull 和 DeleteBehavior.ClientSetNull：

  • client 指 EF，即：EF 会生成解决子 entity 的 Update/Delete 语句，交数据库执行，不依赖于数据库的设定
  • 非 client，需依附数据库上的设定，EF 不会生成解决子 entity 的 Update/Delete 语句

所以，如果设置是：

  • Client：子 entity 要曾经退出 DbContext（比方 1:n 的时候，n 要双向援用且被加载到 DbContext）
  • 非 Client：数据库要有相应的 Cascade 设置。如果通过 Migration 或 EnsureCreated 创立的数据库，数据库上的 Cascade 会主动配置……

演示：

  1. 应用 EF 的 migration 或者 API 建库建表，不同的 DeleteBehavior 生成不同的 SQL 建表语句，比方：

    1. __DeleteBehavior.SetNull，生成 ON DELETE SET NULL

      ALTER TABLE [dbo].[Students] ADD CONSTRAINT [FK_Students_Bed_SleepInId] FOREIGN KEY ([SleepInId]) REFERENCES [dbo].[Bed] ([Id]) ON DELETE __SET NULL__;

      __

    2. DeleteBehavior.ClientCascade，没有 ON DELETE 后缀（_@想一想 @_：为什么？）
  2. 删除一个父 entity，在 Logger 中查看是否有删除 / 更新子 entity 的 SQL 语句

留神： 如果说 EF 的 Cascade 配置和数据库设置相冲突，会报异样。

默认行为

EF 依据子 entity 是否必须要有一个父 entity（即数据库上外键是否能够为 Null），默认设置 Behavior：

  • 如果外键能够为空：DeleteBehavior.ClientSetNull
  • 如果外键不能够为空：DeleteBehavior.Cascade

标记删除

当 entity 之间的关系简单之后，级联删除会导致简单的链式反应，比方：

删除 A 就会删除 B，删除 B 就会删除 C 和 D，删除 D 又会删除 E 和 F……但并不是每个 entity 都能删得掉

所以咱们通常都不进行物理删除，而是用 flag 标记删除（在 entity 中增加一个是否已删除的 Flag 列），最初再由 DBA 批量删除，其劣势为：

  • 缩小用户等待时间
  • 能够回溯撤销
  • 便于管制意外状况产生

删除关系

有时候咱们并不需要删除 entity，只是想“切断”entity 之间的关系。比方：1 号教室原来是 lw、zl、lzb 三个同学，当初将 lzb 移出该教室（而不是删除）。

留神首先要把关联 entity 加载到 DbContext 中来。

SetNull 和 Remove

如果援用是单向的话，无论关联 entity 是汇合还是单个元素。

小 bug

应用 LazyLoad，比方在“多对多”关系中，你可能会认为这样的代码是“从新赋值”

但查看运行后果，居然是“增加”了。这是怎么一回事呢？https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…
https://github.com/hdfgfgh546…
https://www.github.com/hdfgfg…
http://github.com/hdfgfgh546/…

退出移动版