EF的代码优先，如何在不设置数据库表之间外键的情况下定义导航属性关系

Question

I use code first of Entity framework. There are two classes "Question" and "User". I defined a relationship as below:

this.HasRequired(v => v.Creator).WithMany(v => v.Questiones)
.HasForeignKey(v => v.CreatorId).WillCascadeOnDelete(false);

After gernerating the database I found that it always create foreign key between Id of User and CreatorId of Question. Because of lower performance of FK(and other reason),I want to define navigation property relationship without setting foreign key in database? Delete FK after EF created it? If cannot do this using fluent api, could you tell me why EF designed in this way please?

About the lower performance of FK. I have a User table with 5 Million records in it. when I insert a Question into db, since the db check the question.CreatorId validation from User table, it always slower than without FK. And there are many other reasons that I need to remove FK.

I think I am somewhat obsession because I think that deleting FK after created it is strangely and ugly. What i want is implementing this by using something like WithoutForeignKey in fluent api:

this.HasRequired(v => v.Creator).WithMany(v => v.Questiones)
.WithoutForeignKey(v => v.CreatorId).WillCascadeOnDelete(false); 

Answer 1

Without questioning why are you trying to do this strange thing and going just to the answer: you could delete fk constraint after generated, or you could use migrations and remove FK generation from the migration code.

SQL code generated when traversing nav properties will work even if fk constraint doesn't exist, except for cascade deleting

Answer 2

If you want a relationship between two tables, you need to define a foreign key. No way around it. Even if you use Map() in fluent api, you can only hide the foreign key in your model, in the background EF will still use it and it will exist in the database.

Also I don't get what you mean by "performance" of foreign key? One extra (likely small) column won't make a difference. If you mean the navigation properties for the performance part, you can do 3 things:

1. Don't include them in your model
2. Make them non-virtual to disable lazy loading
3. Disable lazy loading all together with ctx.Configuration.LazyLoadingEnabled = false;

Answer 3

If you don't want to tell db about relation and treat both entities as not related (I wonder why), then just ignore these navigation properties and FK field. Note that you will be responsible for managing related entities: saving and loading them from db, updating ids etc

this.Ignore(q => q.Creator);
this.Ignore(q => q.CreatorId);

And you also need to ignore other side of relation, otherwise EF will generate FK column with default name Creator_CreatorId . So in Creator entity configuration:

this.Ignore(c => c.Questiones);