How to define relationships programmatically in Entity Framework 4.1's Code-First Fluent API

Question

I\'m playing around with the new EF4.1 unicorn love.

I\'m trying to understand the different ways I can use code-first to programatically

Answer 1

Lets introduce a few specific classes to illustrate the solutions:

public class Account
{
    public long ID { get; set; }
    public virtual User User { get; set; }
}

public class User
{
    public long ID { get; set; }
    public virtual Account Account { get; set; }
    public virtual Team Team { get; set; }
}

public class Team
{
    public long ID { get; set; }
    public long CompanyID { get; set; }

    public virtual Company Company { get; set; }
    public virtual ICollection Users { get; set; }
}

public class Company
{
    public long ID { get; set; }
}

I'm using a helper class to make the mapping classes a bit less verbose:

internal abstract class AbstractMappingProvider : IMappingProvider where T : class
{
    public EntityTypeConfiguration Map { get; private set; }

    public virtual void DefineModel( DbModelBuilder modelBuilder )
    {
        Map = modelBuilder.Entity();

        Map.ToTable( typeof(T).Name );
    }
}

Now for the mappings. Lets do the "1:1" mapping first. In my example user and account are 1:1 related and share the same primary key (only one of them will be an identity column, which in this case is the Account.ID).

internal class UserMapping : AbstractMappingProvider
{
    public override void DefineModel( DbModelBuilder modelBuilder )
    {
        base.DefineModel( modelBuilder );
        Map.HasRequired( e => e.Account ).WithRequiredDependent( r => r.User ).WillCascadeOnDelete( true );
    }
}

internal class AccountMapping : AbstractMappingProvider
{
    public override void DefineModel( DbModelBuilder modelBuilder )
    {
        base.DefineModel( modelBuilder );
        Map.HasRequired( e => e.User ).WithRequiredPrincipal( r => r.Account ).WillCascadeOnDelete( true );
    }
}   

In the following mappings we specify that a team has (0..n) users, while a single user is in exactly one team (required). We also specify that a team can have a company, but company does not expose a list of teams.

internal class TeamMapping : AbstractMappingProvider
{
    public override void DefineModel( DbModelBuilder modelBuilder )
    {
        base.DefineModel( modelBuilder );
        Map.HasOptional( e => e.Company ).WithMany().HasForeignKey( e => e.CompanyID );
        Map.HasMany( e => e.Users ).WithRequired( r => r.Team );
    }
}   

internal class CompanyMapping : AbstractMappingProvider
{
    public override void DefineModel( DbModelBuilder modelBuilder )
    {
        base.DefineModel( modelBuilder );
    }
}

Hope this helps!