具有单独ID属性的EF6一对一关系 [英] EF6 One-To-One relationship with separate ID property

问题描述

我们需要定义以下实体之间的一对一关系：

We need to define a One-To-One relationship between following entities:

public class Foo
{
    [Key, Column("Foo_ID")]
    public int Id { get; set; }

    public Bar Bar { get; set; }
}

public class Bar
{
    [Key, Column("Bar_ID")]
    public int Id { get; set; }

    [Column("Bar_Foo_ID")]
    public int? FooId { get; set; }

    public Foo Foo { get; set; }   
}

我们需要迁移旧版软件，并使它们同时运行现在。因此，我们无法更改任何关系。不幸的是，数据库中没有定义任何外键。

We need to migrate a legacy software and have both of them running side by side for now. So we can't change any relations. Unfortunately there are no foreign keys defined in the database.

modelBuilder.Entity<Foo>()
            .HasOptional(a => a.Bar)
            .WithRequired(x => x.Foo)
            .WillCascadeOnDelete(true);

当我们查询 Foo 和 Include（x => x.Bar）它使用 LEFT OUTER JOIN条在Foo_ID = Bar_ID 上创建一个SQL查询，这是错误的。

When we query Foo and Include(x => x.Bar) it creates a SQL query with LEFT OUTER JOIN bars ON Foo_ID = Bar_ID which is wrong.

我们需要将其更改为Foo_ID = Bar_Foo_ID 上的 LEFT OUTER JOIN条形，但我不是确保Entity Framework如何支持它，因为我们在数据库中没有外键，而 Bar_ID 作为PrimaryKey。

We need to change this to a LEFT OUTER JOIN bars on Foo_ID = Bar_Foo_ID, but I'm not sure how Entity Framework supports that as we don't have foreign keys in our DB and Bar_ID as PrimaryKey.

我知道一个 Foo 可能有多个 Bars ，但是有一种方法可以强制执行一个一对一关系？

I know that there can be potentially more than one Bars for one Foo, but is there a way to enforce a One-To-One relationship?

创建 Foo 时，会出现一个 Bar 。

推荐答案

对于旧数据，可以使用以下命令：

For legacy data, you can use the following:

1：0-1关系基本上是1：许多关系的一种特殊形式。

1 : 0-1 relationships are basically a special form of 1 : many relationships.

因此您可以将关系配置为1：实体框架中有很多，并可能添加唯一索引到外键属性以强制执行最大约束。

So you can configure the relation as 1:many in entity framework and potentially add a unique index to the foreign key property to enforce your constraint of max. one related entry.

public class Foo
{
    [Key, Column("Foo_ID")]
    public int Id { get; set; }

    // this can't be a single reference property unfortunately... but it will only contain 0 or 1 object when working with it.
    public ICollection<Bar> Bars { get; set; }
}

public class Bar
{
    [Key, Column("Bar_ID")]
    public int Id { get; set; }

    [Index(IsUnique = true)]
    [Column("Bar_Foo_ID")]
    public int? FooId { get; set; }

    public Foo Foo { get; set; }   
}

modelBuilder.Entity<Foo>()
            .HasMany(a => a.Bars)
            .WithRequired(x => x.Foo)
            .HasForeignKey(x => x.FooId)
            .WillCascadeOnDelete(true);

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