是否可以在不知道主键的情况下从DbContext获取具有导航属性的实体

Question

Using EF 6.1 I want to be able to return a single entity from the DbContext, with its navigation properties populated, without knowing the primary key.

So for example the entity:

public class MyEntity
{
    public int SomeSortOfPrimaryKey { get; set; }
    public string SomeProperty { get; set; }
    public virtual SomeOtherEntity SomeOtherEntity { get; set; }
}

I have an instance of the entity available so I have tried:

var entityWithNavProps = _dbContext.Entry(entity).Entity;

But this doesn't get the entity with it's navigation properties. Obviously the .Find() method doesn't work either as it's expecting a string, guid or integer.

Is there any other way to use an entity, and the DbContext to do this?

Thank you.

Answer 1

No, you can't.

You need to supply the reference navigation property's id.

For example, given these models.

public class Book
{
    public int Id { get; set; }
    public int AuthorId { get; set; }
    public User Author { get; set; }
}
public class User
{
    public int Id { get; set; }
    public string Name { get; set; }
}

If you don't provide reference id or you provide invalid id, it will not load the reference.

// AuthorId = 0 is invalid id.
var book = new Book { Id = 1, AuthorId = 0 };
db.Books.Attach(book);
db.Entry(book).Reference(b => b.Author).Load();

When you provide the valid reference id, it will load the reference.

// AuthorId = 1 is a valid id.
var book = new Book { Id = 1, AuthorId = 1 };
db.Books.Attach(book);
db.Entry(book).Reference(b => b.Author).Load();

PS: Unless it's a collection navigation property.