EF 4.1 Code First multiple Many-to-Many relationships - asp.net-mvc-3

Question

I'm having trouble wrapping my head around a certain code-first relationship. I have three entities: Group, User, GroupPermission. The GroupPermission entity holds information about permissions that relate to a group. There are three permissions: leader, editor, user. The GroupPermission table should include the primary key Id and the name of the permission. Then I want a relationship table that looks something like this: Id - Group_Id - User_Username - GroupPermission_Id. There can be multiple groups, multiple users, multiple permissions. I have plenty of examples that help me make a single relationship table, but I can't find anything that includes multiple relationships.
Here are my entities...
User:
public class User
{
[Key, StringLength(EntityLength.UsernameLength)]
public string Username { get; set; }
[Required, StringLength(EntityLength.NameLength)]
public string FirstName { get; set; }
[Required, StringLength(EntityLength.NameLength)]
public string LastName { get; set; }
[Required, StringLength(EntityLength.Email)]
public string Email { get; set; }
public bool Active { get; set; }
public DateTime DateCreated { get; set; }
public virtual UserPermission UserPermission { get; set; }
public virtual ICollection<Group> Groups { get; set; }
public virtual ICollection<Project> Projects { get; set; }
public virtual ICollection<Issue> Issues { get; set; }
public virtual ICollection<GroupPermission> GroupPermissions { get; set; }
public string FullName
{
get { return FirstName + ' ' + LastName; }
}
}
Group:
public class Group
{
[Key]
public int Id { get; set; }
[Required, StringLength(EntityLength.GenericLength)]
public string Name { get; set; }
[Required, StringLength(EntityLength.DescriptionLength)]
public string Description { get; set; }
public virtual ICollection<User> Users { get; set; }
public virtual ICollection<Project> Projects { get; set; }
public virtual ICollection<GroupPermission> GroupPermissions { get; set; }
}
GroupPermission:
public class GroupPermission
{
[Key]
public int Id { get; set; }
[StringLength(EntityLength.GenericLength)]
public string Name { get; set; }
public int GroupId { get; set; }
public virtual ICollection<Group> Groups { get; set; }
public int UserId { get; set; }
public virtual ICollection<User> Users { get; set; }
public enum Permission
{
Leader = 1,
Editor = 2,
User = 3
}
}
When the tables are created using this structure, I get a GroupPermissions table that has Id, Name, GroupId, and UserId. This table needs to only be Id and Name. Then it creates a GroupPermissionUsers table that holds GroupPermissions_Id and User_Username. This is the table that should be Id, Group_Id, User_Username, GroupPermission_Id.
Does anybody have any tips to accomplish this or am I thinking about the design of this incorrectly?

Answer 1

In such case you are missing additional entity. It should look like:
New Permission entity with Id and Name:
public class Permission
{
[Key]
public int Id { get; set; }
[StringLength(EntityLength.GenericLength)]
public string Name { get; set; }
public virtual ICollection<GroupPermission> GroupPermissions { get; set; }
}
Modified GroupPermission entity to form junction table among Users, Groups and Permissions:
public class GroupPermission
{
[Key]
public int Id { get; set; }
public int GroupId { get; set; }
public virtual Group Group { get; set; }
public string UserName { get; set; }
[ForeignKey("UserName")]
public virtual User User { get; set; }
public int PermissionId { get; set; }
public virtual Permission Permission { get; set; }
}