Code First adding to collections? How to use Code First with repositories?

Question

EDIT: This happen only on larger scale projects with repositories. Is there anybody using EF4 with CodeFirst approach and using repositories? Please advise me.

Hi. I

Answer 1

Removing the "virtual" keyword from the collection properties works around the problem, by preventing the Entity Framework from creating a change tracking proxy. However, this is not a solution for many people, because change tracking proxies can be really convenient and can help prevent issues when you forget to detect changes at the right places in your code.

A better approach would be to modify your POCO classes, so that they instantiate the collection properties in their get accessor, rather than in the constructor. Here's the original Author POCO class, modified to allow change tracking proxy creation:

public class Author
{
    public virtual int AuthorId { get; set; }
    public virtual string Name { get; set; }

    private ICollection _books;

    public virtual ICollection Books
    {
        get { return _books ?? (_books = new Collection()); }
        set { _books = value; }
    }

    public void AddBook(Book book)
    {
        book.Author = this;
        Books.Add(book);
    }
}

In the above code the collection property is no longer automatic, but rather has a backing field. It's better if you leave the setter protected, preventing any code (other than the proxy) from subsequently modifying these properties. You will notice that the constructor was no longer necessary and was removed.