Question

Here’s My Code:

public class RegisteredUser
{
    public virtual int ID { get; set; }
    [Required]
    public virtual string FirstName { get; set; }
    [Required]
    public virtual string LastName { get; set; }
    [Required]
    public virtual string Email { get; set; }
    [Required]
    [DataType(DataType.Password)]
    public virtual string Password { get; set; }
    public virtual string NickName { get; set; }
    [Required]
    [DataType(DataType.Date)]
    public virtual DateTime DOB { get; set; }
    public virtual string Avatar { get; set; }
    public virtual ICollection<Post> Posts { get; set; }
    public virtual ICollection<CommentPost> CommentPosts { get; set; }
    public virtual ICollection<TagPost> TagPosts { get; set; }
    public virtual ICollection<RegisteredUser> Friends { get; set; }
}

public class SocialWeb_BasedApplicationDB : DbContext
{
    public DbSet<RegisteredUser> RegisteredUsers { get; set; }
    public DbSet<Post> Posts { get; set; }
    public DbSet<CommentPost> CommentPosts { get; set; }
    public DbSet<TagPost> TagPosts { get; set; }

    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        modelBuilder.Entity<Post>().HasMany(m => m.CommentPost).WithRequired(a => a.Post).WillCascadeOnDelete(false);
        modelBuilder.Entity<RegisteredUser>().HasMany(m => m.TagPosts).WithRequired(a => a.RegisteredUser).WillCascadeOnDelete(false);
        modelBuilder.Entity<RegisteredUser>().HasMany(a => a.Friends).WithMany().Map(a => a.MapLeftKey("UserID").MapRightKey("FriendID").ToTable("Users_Friends"));
    }

The Many To May table is created but i can’t actually use it like i can’t do (from n in Context.User_Friends where n.UserId = 0 select n);

what should i do?

Answer 1

From EF’s perspective, User_Friends is not an entity instead to get the friends of a User you have to use this query

var friends = from u in Context.RegisteredUsers
              from f in u.Friends
              where u.UserId=0
              select f;

I usually make relationships into explicit entities because there is more information that is useful about these relationships that can’t be captured otherwise.