How to fix: The number of properties in the Dependent and Principal Roles in a relationship constraint must be identical?

Question

I am using Entity Framework 4.3.1 against a SQL Server 2012 database and I am using the POCO approach. I am getting the following error and I am wondering if anyone can explain how to fix it:

ModelValidationException

One or more validation errors were detected during model generation: \tSystem.Data.Entity.Edm.EdmAssociationConstraint: : The number of properties in the Dependent and Principal Roles in a relationship constraint must be identical.

There is no InnerException available for any further information.

I cannot change the database schema and it is a little odd, but here it is...

• ** are the primary key (notice I have composite primary keys)
• (FK) Denotes a foreign key

Here are the tables (if it helps I can post the SQL to generate them but I do not think the tables are actually the problem as the exception is in the validation of the model):

One - **OneId int not null **TwoId int not null (FK) **ThreeId int not null (FK) Name nvarchar(50) not null  Two - **TwoId int not null **ThreeId int not null (FK) Name nvarchar(50) not null  Three - **ThreeId not null Name nvarchar(50) not null 

Here are the entities (notice that I am including the foreign keys in the model but other than that pretty standard):

public class Three {     public int ThreeId { get; set; }     public string Name { get; set; }     public virtual ICollection<Two> Twos { get; private set; }     public virtual ICollection<One> Ones { get; private set; }      public void AddOne(One one)     {         if (one == null)             throw new ArgumentNullException("two");          if (Ones == null)             Ones = new List<One>();          if (!Ones.Contains(one))             Ones.Add(one);          one.Three = this;     }      public void AddTwo(Two two)     {         if (two == null)             throw new ArgumentNullException("two");          if (Twos == null)             Twos = new List<Two>();          if (!Twos.Contains(two))             Twos.Add(two);          two.Three = this;     } }  public class Two {     public int TwoId { get; set; }     public int ThreeId { get; set; }     public string Name { get; set; }     public virtual Three Three { get; set; }     public virtual ICollection<One> Ones { get; private set; }      public void AddOne(One one)     {         if (one == null)             throw new ArgumentNullException("two");          if (Ones == null)             Ones = new List<One>();          if (!Ones.Contains(one))             Ones.Add(one);          one.Two = this;     } }  public class One {     public int OneId { get; set; }     public int TwoId { get; set; }     public int ThreeId { get; set; }     public virtual Two Two { get; set; }     public virtual Three Three { get; set; } } 

And here is the data context:

public class DbCtx : DbContext {     public DbCtx(string connectionString)         : base(connectionString)     {         Ones = Set<One>();         Twos = Set<Two>();         Threes = Set<Three>();     }      public DbSet<One> Ones { get; private set; }     public DbSet<Two> Twos { get; private set; }     public DbSet<Three> Threes { get; private set; }      protected override void OnModelCreating(DbModelBuilder modelBuilder)     {         var one = modelBuilder.Entity<One>();         one.ToTable("One");          one.HasKey(d => new                             {                                 d.OneId,                                 d.TwoId,                                 d.ThreeId                             });          one.Property(d => d.OneId)             .HasDatabaseGeneratedOption(DatabaseGeneratedOption.None);          one.HasRequired(t => t.Two)             .WithMany(s => s.Ones)             .HasForeignKey(t => t.TwoId);          one.HasRequired(t => t.Three)             .WithMany(s => s.Ones)             .HasForeignKey(t => t.ThreeId);          var two = modelBuilder.Entity<Two>();         two.ToTable("Two");          two.HasKey(d => new                             {                                 d.TwoId,                                 d.ThreeId                             });          two.Property(p => p.TwoId)             .HasDatabaseGeneratedOption(DatabaseGeneratedOption.None);          two.HasRequired(t => t.Three)             .WithMany(s => s.Twos)             .HasForeignKey(t => t.ThreeId);          var three = modelBuilder.Entity<Three>();         three.ToTable("Three");         three.HasKey(s => s.ThreeId);          three.Property(p => p.ThreeId)             .HasDatabaseGeneratedOption(DatabaseGeneratedOption.None);          base.OnModelCreating(modelBuilder);     } } 

Finally, this is a snippet of code to cause the exception:

using (var ctx = new DbCtx(@".....")) {     Console.WriteLine(ctx.Twos.Count()); } 

Answer 1

The reason for the error are incorrectly configured relations in your model. This is not correct:

    one.HasRequired(t => t.Two)         .WithMany(s => s.Ones)         .HasForeignKey(t => t.TwoId);      one.HasRequired(t => t.Three)         .WithMany(s => s.Ones)         .HasForeignKey(t => t.ThreeId); 

It should be:

    one.HasRequired(t => t.Two)         .WithMany(s => s.Ones)         .HasForeignKey(t => new { t.TwoId, t.ThreeId }); 

Because dependent's FK must contain all columns of principal PK. You must also remove navigation property from Three to One.