Question

I am using EF5 (Code 1st) and doing all my configurations with the Fluent API. My model looks like this:

public class AddressType    
{
    public int    AddressTypeID { get; set; }
    public string Name          { get; set; }
}
public class Address
{
    public int    AddressID  { get; set; }
    public int    StateID    { get; set; }

    public string Street     { get; set; }
    public string City       { get; set; }
    public string PostalCode { get; set; }

    public State State                { get; set; }
    public ICollection<Person> People { get; set; }
}
public class Person
{
    public int      PersonID    { get; set; }
    public string   Name        { get; set; }

    public ICollection<Address> Addresses { get; set; }
}

My database contains tables for the above classes + the below Many:Many table:

Person.Person2Address
(
    PersonID      INT NOT NULL,
    AddressID     INT NOT NULL,
    AddressTypeID INT NOT NULL,
)

The 3 fields above are all foreign keys & the 3 together make up the Primary Key for the table.

Typically my M:M setups only involve 2 fields in the PK. And I would map it like this:

var addressCfg = mb.Entity<Address>();
addressCfg.ToTable("Address", "Geo");
addressCfg.HasMany(a => a.People)
          .WithMany(p => p.Addresses)
          .Map(mmc =>
          {
             mmc.ToTable("Person2Address", "Person");
             mmc.MapLeftKey("AddressID");
             mmc.MapRightKey("PersonID");
          });

But I don’t know how to configure this 3rd field in the PK or how CRUD would even work in EF in this case.

Any examples of how this should be handled would be greatly appreciated.

Answer 1

You can’t map this as many-to-many relationship. You need three one-to-many relationships with an intermediate additional entity Person2Address that represents the link table with the three keys. The collections in Person and Address must both refer to this intermediate entity (and optionally also a collection in AddressType).

The model would be like this:

public class AddressType
{
    public int AddressTypeID { get; set; }
    public string Name { get; set; }

    // public ICollection<Person2Address> Person2Addresses { get; set; }
    // optionally you can include this collection or not
}

public class Address
{
    public int AddressID { get; set; }
    public int StateID { get; set; }

    public string Street { get; set; }
    public string City { get; set; }
    public string PostalCode { get; set; }

    public State State { get; set; }
    public ICollection<Person2Address> Person2Addresses { get; set; }
}

public class Person
{
    public int PersonID { get; set; }
    public string Name { get; set; }

    public ICollection<Person2Address> Person2Addresses { get; set; }
}

public class Person2Address
{
    public int PersonID { get; set; }
    public int AddressID { get; set; }
    public int AddressTypeID { get; set; }

    public Person Person { get; set; }
    public Address Address { get; set; }
    public AddressType AddressType { get; set; }
}

And the mapping with Fluent API:

modelBuilder.Entity<Person2Address>()
    .HasKey(p2a => new { p2a.PersonID, p2a.AddressID, p2a.AddressTypeID });

modelBuilder.Entity<Person2Address>()
    .HasRequired(p2a => p2a.Person)
    .WithMany(p => p.Person2Addresses)
    .HasForeignKey(p2a => p2a.PersonID);

modelBuilder.Entity<Person2Address>()
    .HasRequired(p2a => p2a.Address)
    .WithMany(a => a.Person2Addresses)
    .HasForeignKey(p2a => p2a.AddressID);

modelBuilder.Entity<Person2Address>()
    .HasRequired(p2a => p2a.AddressType)
    .WithMany()
    .HasForeignKey(p2a => p2a.AddressTypeID);

Or use WithMany(at => at.Person2Addresses) in the last mapping if you want to include the collection in AddressType.