Entity Framework Code-First - Define the key for this EntityType

Question

Hi I'm planning to test EF Code First in one of my project. This is what I want actually. I have three tables and the structure is as follows

public partial class App_user
    {
        public int id { get; set; }
        public string name { get; set; }
        public string email_address { get; set; }
        public string password { get; set; }
        public int user_type { get; set; }
        public List<Role> Roles { get; set; }
    }

public partial class Role
    {
        public int id { get; set; }
        public string name { get; set; }
    }
public partial class User_role
    {
        public int user_id { get; set; }
        public int role_id { get; set; }
        public virtual Role Role { get; set; }
        public virtual App_user App_user { get; set; }
    }

In the third table there is no primary key. So it gives an error while running. Here is the error message -

System.Data.Edm.EdmEntityType: : EntityType 'User_role' has no key defined. Define the key for this EntityType. System.Data.Edm.EdmEntitySet: EntityType: The EntitySet User_roles is based on type User_role that has no keys defined.

Why its is happening? Is there a solution for this?

Solution 1

If think you are trying to model many-to-many relation between user and role. In such case your model is completely wrong.

Use this instead:

public partial class App_user
{
    public int id { get; set; }
    public string name { get; set; }
    public string email_address { get; set; }
    public string password { get; set; }
    public int user_type { get; set; }
    public virtual ICollection<Role> Roles { get; set; }
}

public partial class Role
{
    public int id { get; set; }
    public string name { get; set; }
    public virtual ICollection<User> Users { get; set; }
}

This will create many-to-many automatically and you will not need to bother with junction table. If you need to expose junction table you must use this:

public partial class App_user
{
    public int id { get; set; }
    public string name { get; set; }
    public string email_address { get; set; }
    public string password { get; set; }
    public int user_type { get; set; }
    public virtual ICollection<User_Role> UserRoles { get; set; }
}

public partial class Role
{
    public int id { get; set; }
    public string name { get; set; }
    public virtual ICollection<User_Role> UserRoles { get; set; }
}

public partial class User_role
{
    [Key, ForeignKey("App_user"), Column(Order = 0)]
    public int user_id { get; set; }
    [Key, ForeignKey("Role"), Column(Order = 1)]
    public int role_id { get; set; }
    public virtual Role Role { get; set; }
    public virtual App_user App_user { get; set; }
}

Exposing junction table is meaningless if you don't need additional properties in it.

To your error - each entity in Entity framework must have primary key defined.

Solution 2

You can simply do like this:

public partial class User_role
{
    [Key]
    public int user_id { get; set; }
    [Key]
    public int role_id { get; set; }
    public virtual Role Role { get; set; }
    public virtual App_user App_user { get; set; }
}

Solution 3

Because I used an ADO.net Entiry Data Model with automated generated code I didn't want to change the Model classes so I changed the WebApiConfig.cs to define the keys of the underlying models:

ODataConventionModelBuilder builder = new ODataConventionModelBuilder();
EntitySetConfiguration<Registration> EntitySetConfiguration_Registration = builder.EntitySet<Registration>("Registration");
EntitySetConfiguration<Lead> EntitySetConfiguration_Lead = builder.EntitySet<Lead>("Lead");
EntitySetConfiguration<Session> EntitySetConfiguration_Session = builder.EntitySet<Session>("Session");
EntitySetConfiguration_Registration.EntityType.HasKey(p => p.Registration_Id);
EntitySetConfiguration_Lead.EntityType.HasKey(p => p.Lead_Id);
EntitySetConfiguration_Session.EntityType.HasKey(p => p.Session_Id);
config.Routes.MapODataRoute("odata", "odata", builder.GetEdmModel());

Comments

[archil]

wouldn't that make user_id key? What if user is in many roles?

[Yngve B-Nilsen]

what about something like that?

[Mukesh]

[Key, ForeignKey("App_user"), Column(Order = 0)] - What is the namespace to use with it?

[Ladislav Mrnka]

System.ComponentModel.DataAnnotations (it has also separate assembly).

[Abhijeet]

@LadislavMrnka, I do not seem to apply [Key, ForeignKey("App_user"), Column(Order = 0)], only [Key] is available, what am I missing ? Thanks.

[Ladislav Mrnka]

@autrevo: Make sure you are referencing EntityFramework.dll. .NET 4.0 does not contain those annotations directly (.NET 4.5 does).

[CodeEngine]

@YngveB.Nilsen how do you add the [Key] Property ? I refered System.ComponentModel.DataAnnotation. But it only shows [foreignkey] is [key] under a diferent directory ?

[Yngve B-Nilsen]

@omachu23 back in 2011 (when this answer was written) it was in System.ComponentModel.DataAnnotation, but what it is today is a different question :)

[AceMark]

the ForeignKey("") is not really necessary.