Entity framework many-to-many relationship

user2915962 Published at Dev

user2915962

Ok, I'm trying to figure out how to setup my DB properly.

I have two classes:

public class Event
{
    public int EventId { get; set; }
    public string EventName { get; set; }
}

and

public class Dog
{
    public int DogId { get; set; }
    public string Name { get; set; }
    public int Age { get; set; }
}

An event must be able to contain a collection of dogs. Every dog must be able to be part in any event. I'm guessing this is what they call a many-to-many relationship, but I do not now how to set it up with keys etc. I hope I'm clear enough with what I'm hoping to achieve.

I asked a similar question yesterday but I was then not clear over what I needed: Have a list of objects as a foreign key.

Thanks!

StuartLC

Yes, that is a N:N relationship. Assuming Code First, change your entities:

public class Event
{
    public Event()
    {
       Dogs = new HashSet<Dog>();
    }
    public int EventId { get; set; }
    public string EventName { get; set; }
    public virtual ICollection<Dog> Dogs { get; set; }
}

public class Dog
{
    public Dog()
    {
       Events = new HashSet<Event>();
    }
    public int DogId { get; set; }
    public string Name { get; set; }
    public int Age { get; set; }
    public virtual ICollection<Event> Events { get; set; }
}

And your OnModelCreating:

protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
  modelBuilder.Entity<Dog>()
    .HasMany(d => d.Events)
    .WithMany(e => e.Dogs)
    .Map(m =>
    {
       m.MapLeftKey("DogId");
       m.MapRightKey("EventId");
       m.ToTable("DogEvent");
    });
}

This should then create a junction table DogEvent with just the two foreign keys, DogId and EventId

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