Question

A little new to EF, so please bear with me if the answer to this is obvious. I’m doing a tutorial that uses EF, and two DbSets are defined like this:

    public DbSet<BrokerageAccount> BrokerageAccounts { get; set; }
    public DbSet<Customer> Customers { get; set; }

The customer class looks like this– it’s a POCO (some code cut for brevity):

public class Customer
{
    public Customer()
    {
        BrokerageAccounts = new HashSet<BrokerageAccount>();
    }

    // Primitive properties
    public int Id { get; set; }
    public string FirstName { get; set; }
    public string LastName { get; set; }

    // Navigation properties
    public ICollection<BrokerageAccount> BrokerageAccounts { get; set; }
}

}

The BrokerageAccount class is a POCO as well, very similar in design to Customer.

So far so good. The code I have a question about is below. There is an association made in the main program between Customer and BrokerageAccount that I don’t follow. The code reads like this:

    public Customer GetCustomer(string custId)
    {
        using (var context = DataContext)
        {
            return context.Customers
                .Include("BrokerageAccounts").SingleOrDefault(c => c.CustomerCode == custId);
        }
    }

I can’t figure out how the association/join is made between Customer and BrokerageAccount. I don’t see any config or other files in my VS 2010 project that tells what associates the two DbSets, what foreign key column to use, etc.

Perhaps I’m missing something obvious or a mapping file of some sort, but just because Customer has an ICollection of BrokerageAccount along with a comment above that says “Navigation Properties”, doesn’t make it so. In EF, how are those associations established?

Answer 1

The normal way of setting up the navigation properties is to use the ModelBuilder, This gives you a fluent api to set up the associations, take a look at this for some in depth stuff about how you go about this.

http://xhalent.wordpress.com/2011/01/21/configuring-entity-framework-4-codefirst/

Entity framework will guess at what you meant if you dont set up the nav properties manually, in the above case it will probably set up your nav properties as expected as you only have a single 1-* relationship between customer and BrokerageAccount which appears to be named sensibly.

There is also an attribute method that you can use to set up the navigation properties.