How do I map a composite primary key in Entity Framework 4 code first?

Question

I\'m getting to grips with EF4 code first, and liking it so far. But I\'m having trouble mapping an entity to a table with a composite primary key.

The configuration

Answer 1

I will try to explain it step by step, using the following Entity

public class Account
{
    public int AccountId1 { get; set; }
    public int AccountId2 { get; set; }
    public string Description { get; set; }
}

1. Create a class derived from the EntityTypeConfiguaration Object to override the conventions

   class AccountEntityTypeConfiguration : EntityTypeConfiguration
   {
   
       public AccountEntityTypeConfiguration()
       {
         // The Key
         // The description of the HasKey Method says
         // A lambda expression representing the property to be used as the primary key.
         // If the primary key is made up of multiple properties then specify an anonymous type including the properties.
         // Example C#: k => new { k.Id1, k.Id2 }
         // Example VB: Function(k) New From { k.Id1, k.Id2 }
         this.HasKey(k => new { k.AccountId1, k.AccountId2 } );  // The Key
   
         // Maybe the key properties are not sequenced and you want to override the conventions
         this.Property(p => p.AccountId1).HasDatabaseGeneratedOption(System.ComponentModel.DataAnnotations.Schema.DatabaseGeneratedOption.None);
         this.Property(p => p.AccountId2).HasDatabaseGeneratedOption(System.ComponentModel.DataAnnotations.Schema.DatabaseGeneratedOption.None);
   
         this.Property(p => p.Description).IsRequired();  // This property will be required
         this.ToTable("Account");  // Map the entity to the table Account on the database
       }
   }
   

2. When create the class derived from the DbContext Object, override OnModelCreating Method and add a new AccountEntityTypeConfiguration object to the Configurations of the model Builder.

   public class MyModelAccount : DbContext
   {
       public DbSet Accounts { get; set;}
   
       protected override void OnModelCreating(DbModelBuilder modelBuilder)
       {
           // Add a new AccountEntityTypeConfiguration object to the configuration of the model, that will be applied once the model is created. 
           modelBuilder.Configurations.Add(new AccountEntityTypeConfiguration());
       }
   
   }
   

Hope it helps you!