Imagine three entities (Customer, Book, Author) related like this:
A Customer has many Books
A Book has one Author
I use that data to print a report like this:
Customer: Peter Book: To Kill a Mockingbird - Author: Harper Lee Book: A Tale of Two Cities - Author: Charles Dickens Customer: Melanie Book: The Hobbit - Author: J. R. R. Tolkien
When I query for Customers I get, as expected, a bunch of queries of the following nature
I can reduce the number of queries by including the books like so:
var customers = db.Customers.Include(c => c.Books);
But I don't know how to load the third level (Author). How can I do that?
There's an overload for
Include that accepts a string which can denote the full path to any extra properties you need:
var customers = db.Customers.Include("Books.Author");
It looks strange because "Author" isn't a property on a collection of books (rather a property on each individual book) but it works. Give it a whirl.
Also, it isn't necessary to use the string overload. This method will work too:
var customers = db.Customers.Include(c => c.Books.Select(b => b.Author));
For more examples see the EF team blog post: http://blogs.msdn.com/b/adonet/archive/2011/01/31/using-dbcontext-in-ef-feature-ctp5-part-6-loading-related-entities.aspx