您如何确保首先对 EF 代码中的表关系启用级联删除?

问题描述

我想使用代码优先在表上启用级联删除.当模型从头开始重新创建时，即使关系是自动设置的，也不会设置 CASCADE DELETE.奇怪的是，它确实为某些具有多对多关系的表启用了此功能，但您会认为它可能存在问题.

I would like to enable CASCADE DELETE on a table using code-first. When the model is re-created from scratch, there is no CASCADE DELETE set even though the relationships are set-up automatically. The strange thing is that it DOES enable this for some tables with a many to many relationship though, which you would think it might have problems with.

设置:表 A <- 表 B.

Setup:Table A <- Table B.

表 B 的 FK 指向表 A 的 PK.

Table B's FK points to Table A's PK.

为什么这行不通?

推荐答案

你没有得到级联删除的可能原因是你们的关系是可选的.示例:

Possible reason why you don't get cascading delete is that your relationship is optional. Example:

public class Category
{
    public int CategoryId { get; set; }
}

public class Product
{
    public int ProductId { get; set; }
    public Category Category { get; set; }
}

在这个模型中，你会得到一个 Product 表，它有一个 Category 表的外键，但这个键可以为空，并且默认情况下数据库中没有级联删除设置.

In this model you would get a Product table which has a foreign key to the Category table but this key is nullable and there is no cascading delete setup in the database by default.

如果您想拥有所需的关系，那么您有两个选择:

If you want to have the relationship required then you have two options:

注释:

public class Product
{
    public int ProductId { get; set; }
    [Required]
    public Category Category { get; set; }
}

流畅的 API:

modelBuilder.Entity<Product>()
            .HasRequired(p => p.Category)
            .WithMany();

在这两种情况下，都会自动配置级联删除.

In both cases cascading delete will be configured automatically.

如果你想拥有可选但带有级联删除的关系，你需要明确地配置:

If you want to have the relationship optional but WITH cascading delete you need to configure this explicitely:

modelBuilder.Entity<Product>()
            .HasOptional(p => p.Category)
            .WithMany()
            .WillCascadeOnDelete(true);

在最后一段代码中，您也可以简单地编写.WillCascadeOnDelete().此无参数重载默认为 true 以设置级联删除.

In the last code snippet you can also simply write .WillCascadeOnDelete(). This parameterless overload defaults to true for setting up cascading delete.

在文档中查看更多相关信息

See more on this in the documentation

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