防止实体框架在数据库中创建外键

Question

I have a code-first database with the following POCOs:

public Foo {
    public int FooId { get; set; }
    public virtual ICollection<Bar> Bars { get; set; }
}

public Bar {
    public int BarId { get; set; }
    public virtual Foo DefaultFoo { get; set; }
    public virtual ICollection<Foo> Foos { get; set; }
}

This creates the following tables in the database:

Foo

FooId (PK, int, not null)
Bar_BarId (FK, int, null)

Bar

BarId (PK, int, not null)
DefaultFoo_FooID (FK, int, null)

FooBar

Bar_BarId (PK, FK, int, not null)
Foo_FooId (PK, FK, int, not null)

As you can see the Foo table gets a foreign key relation to the Bar table even if the Foo POCO does not have a one-to-one navigation property to the Bar POCO.

However, if I remove the DefaultFoo property from Bar this foreign key is removed.

And, if I leave DefaultFoo in, but remove Bars from Foo and Foos from Bar this foreign key is removed.

In other words, this foreign key is only present if both DefaultFoo and Foos is present on Bar .

How can I make Entity Framework not create this unneccessary foreign key (preferrably without using FluentApi)?

Answer 1

my guess is:

• Foo.Bar_BarId is for Bar.Foos
• Bar.DefaultFoo_FooId is for Bar.DefaultFoo
• FooBar table is for Foo.Bars

I do not/can not say why.

But For me you have to help de default behavior by using some configuration method: fluent or annotations to explicitly set the many/many relation.

You can challenge that by using linqpad and check the generated sql for some queries.

Answer 2

I try your model and Junction table (FoosBars) is not created. The columns created is for the 2 1-many Foo.Bars and Bar.Foos properties and for the 1-1 Bar.DefaultFoo.

I think that in this case the only way is to configure nm relationship using HasMany/WithMany fluent API. In this case EF works as expected.