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 I've tried looks like this:

public SubscriptionUserConfiguration()      {                 Property(u => u.SubscriptionID).IsIdentity();                 Property(u => u.UserName).IsIdentity();     } 

Which throws this exception: Unable to infer a key for entity type 'SubscriptionUser'.

What am I missing?

Answer 1

You could also use

HasKey(u => new { u.SubscriptionID, u.UserName }); 

Edit:

One limitation I have found is that the following do not work:

public ProjectAssignmentConfiguration() {     HasKey(u => u.Employee.EmployeeId);     HasKey(u => u.Project.ProjectId); } 

or

public ProjectAssignmentConfiguration() {     HasKey(u => new { u.Employee.EmployeeId, u.Project.ProjectId }); } 

So how do you set up an entity where the join table has a primary key that is composed of foreign keys?

Answer 2

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<TEntity> Object to override the conventions

   class AccountEntityTypeConfiguration : EntityTypeConfiguration<Account> {      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<Account> 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!