Using entity framework code first in MVC 3

Question

I'm very new at this, I'd really like some help with this problem:

First I already have a database, say I have 3 tables in this database: User, UserMapping, UserRole. I generated a model with 3 class as follows:

public class user
{
 public int UserID { get; set; }
 public string UserName { get; set; }
 public virtual ICollection<UserMapping> UserMappings { get; set; }
}
 public class UserMapping
 {
 public int UserMappingID { get; set; }
 public int UserID { get; set; }
 public int UserRoleID { get; set; }
 public virtual User User { get; set; }
 public virtual UserRole UserRole { get; set; }
 }
 public class UserRole
 {
 public int UserRoleID { get; set; }
 public string RoleName { get; set; }
 public virtual ICollection<UserMapping> UserMappings { get; set; }
 }

I want to create a new user, and add a User Role for the new user. User and User Role have no direct relationship. I want to make a view to create a new user, using the User model class with strongly-typed. How can I make a User Role for the user in this view?

Please help...! Thank you very much in advance.

• gdoron: Learn the basics first, with pluralsight.
• Craig O: You don't need the UserMapping class it can be inferred from the relationship between User and UserRole. The user has a collection of roles and the roles have a collection of users. Entity Framework will automatically create the supporting table (what you call UserMapping).

Answer 1

You don't need to create UserMapping entity by your self . Because when you specify your many to many relationship between User and UserRole EF will automatically create the relationship table UserUserRole relationship table for you.

 public class User
 {
 public int UserID { get; set; }
 public string UserName { get; set; }
 public virtual ICollection<UserRole> UserRoles{ get; set; }
 }
 public class UserRole
 {
 public int UserRoleID { get; set; }
 public string RoleName { get; set; }
 public virtual ICollection<User> Users { get; set; }
 }

Then you can map the relationship table to the existing one,

protected override void OnModelCreating(ModelBuilder modelBuilder)
{
modelBuilder.Entity<User>().HasMany(u => u.UserRoles)
 .WithMany(r => r.Users )
 .Map(m =>
 {
 m.MapLeftKey("UserID");
 m.MapRightKey("UserRoleID");
 m.ToTable("YourExistinegTableName");
 });
}

• user1159872: First of all, thank you so much for your help! I'm using an existing database. This database is also used for other projects, I can't alter the database. I tried your method and didn't use data mapping and got error messages that says required property "user mapping" does not exist. Do you know of another way? Thanks again.
• Jayantha Lal Sirisena: You can map the relationship table to existing one. See I have added the code.