Many-to-Many Relationships to Same Table with EF

debugcn Published at Dev

paul simmons

I have a table where I need many to many relationships, an example can be a social network where friendships are kept. e.g.:

public class User
{
    public int UserId { get; set; }
    public string UserName { get; set; }
}

corresponding to table

CREATE TABLE Users (
UserId int,
UserName varchar(255)
);

I need to have a table like:

CREATE TABLE Friendships(
UserId1 int,
UserId2 int
);

where both fields are related to Users.UserId. How can I achieve this with annotations in EF?

Lars Anundskås

Something like this would do it

public class User
{
    public int UserId { get; set; }
    public string UserName { get; set; }

    public ICollection<User> FriendShips { get; set; }
    public User()
    {
        FriendShips = new HashSet<User>();
    }
}


public class SocialContext : DbContext
{
    public DbSet<User> Users { get; set; }

    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        base.OnModelCreating(modelBuilder);

        modelBuilder.Entity<User>()
        .HasMany(p => p.FriendShips)
        .WithMany()
        .Map(mc =>
        {

            mc.ToTable("userfriends");
        });
    }
}

A single list for each user will keep each users list of friends

Test:

    using (SocialContext ctx = new SocialContext())
    {
        User u = new User()
        {
            UserName = "John"
        };

        User uu = new User()
        {
            UserName = "Jack"
        };

        uu.FriendShips.Add(u);
        u.FriendShips.Add(uu);

        ctx.Users.Add(u);

        ctx.SaveChanges();
    }

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