Property name in a type must be unique

Question

I am using Entity Framework 5 and I have the following entities:

public class User {
  public Int32 Id { get; set; }
  public String Username { get; set; }    
  public virtual ICollection<CLaim> CLaims { get; set; }
}

public class Claim {
  public Int32 Id { get; set; }
  public String Type { get; set; }
  public String Value { get; set; }
  public virtual User User { get; set; }
}

A few notes about these entities:

1. In User entity the Id is the PK;
2. In Claim entity the Id is a FK and is equal to User.Id;
3. In Claim entity the PK is composite from (Id, Type, Value)

So I have the following SQL for these entities:

create table dbo.Users
(
  Id int identity not null 
    constraint PK_Users_Id primary key clustered (Id),  
  Username nvarchar (120) not null
    constraint UQ_Users_Username unique (Username)
);

create table dbo.Claims
(
  Id int not null,
  [Type] nvarchar (200) not null,
  Value nvarchar (200) not null,
    constraint PK_Claims_Id_Type_Value primary key (Id, [Type], Value),
);

alter table dbo.Claims
add constraint FK_CLaims_Id foreign key (Id) 
    references dbo.Users(Id) on delete cascade on update cascade;

Finally, the configuration of the entities are as follows:

internal class UserConfiguration : EntityTypeConfiguration<User> {
  internal UserConfiguration() : base() {
    ToTable("Users");
    HasKey(x => x.Id);
    Property(x => x.Id).IsRequired().HasDatabaseGeneratedOption(DatabaseGeneratedOption.Identity);
    Property(x => x.Username).IsRequired().HasMaxLength(120);
  }
}

internal class ClaimConfiguration : EntityTypeConfiguration<Claim> {
  internal ClaimMapper() : base() {
    ToTable("Claims");
    HasKey(x => new { x.Id, x.Type, x.Value });
    Property(x => x.Id).IsRequired().HasDatabaseGeneratedOption(DatabaseGeneratedOption.None);
    Property(x => x.Type).IsRequired().HasMaxLength(200);
    Property(x => x.Value).IsRequired().HasMaxLength(200);

    HasRequired<User>(x => x.User).WithMany(y => y.Claims).Map(z => { z.MapKey("Id"); });
  }
}

THE PROBLEM:

When I try to create a user I get the following error:

Each property name in a type must be unique. Property name 'Id' was already defined.

Does anyone knows what I might be doing wrong?

Answer 1

MapKey is only used if your foreign key column is not exposed as a property in your model. But in your case it is - as property Claim.Id. In that case you must use HasForeignKey instead of MapKey:

HasRequired<User>(x => x.User)
    .WithMany(y => y.Claims)
    .HasForeignKey(x => x.Id);

Answer 2

In addition to Slauma's answer

HasForeignKey is not available for 1:1, if you still need it you can simply use WithMany without parameters

HasRequired<User>(x => x.User).WithMany().HasForeignKey(x => x.Id);
HasRequired(x => x.City).WithMany().HasForeignKey(x => x.CityId);