How to set a 0..* relationship in Entity Framework Code First?

Question

I have the next code for two classes:

public class Object
{
    public int ObjectID { get; set; }

    public int Object2ID { get; set; }
    public virtual Object2 Object2 { get; set; }
}

public class Object2
{
    public int Object2ID { get; set; }

    public virtual ICollection<Object> Objects { get; set; }
}

I know that with Entity Framework, this will create a one-to-many relationship, but what I want to know, is how to transform this to a zero-to-many relationship.

I'm new to Entity Framework and I couldn't find any direct answer around.

It's still one to many relationship, the difference only either to have required Principal or optional Principal on Dependent. — Yuliam Chandra, Sep 17 '14 at 16:18
I agree, I can't see how you can have a 0 to anything relationship if there's 0 of something then it can't relate to anything. — Ben Robinson, Sep 17 '14 at 16:18
Just a fyi, normal nomenclature you don't use `∞` as it is a special character and some systems may not like the Unicode. Normally you would express it as `0..*` and that is what you will see in most documentation refrences. — Scott Chamberlain, Sep 17 '14 at 17:31

score 11 · Accepted Answer · answered Sep 17 '14 at 16:14

11

For a 0-to-many relationship in Entity Framework, have the foreign key be nullable.

public int? Object2ID { get; set; }

answered Sep 17 '14 at 16:14

UtopiaLtd

2,520
1
30
46

Do I need to set public virtual Object2 Object2 { get; set; } As nullable too, or only the key? – Jorge Díaz Sep 17 '14 at 16:15
No. As a class, Object2 can already be set to null if needed. – UtopiaLtd Sep 17 '14 at 16:24
1

@user3552621 It's nullable "by nature". By the way, you don't NEED to have Object2ID in class Object. – Raphaël Althaus Sep 17 '14 at 16:24

score 3 · Answer 2 · answered Dec 22 '16 at 13:22

Another way to do this is by using Fluent API:

public class YouDbContext : DbContext
{
    protected override void OnModelCreating(DbModelBuilder mb)
    {
        mb.Entity<Object2>
            .HasMany(o1 => o1.Objects)
            .WithOptional(o2 => o2.Object2);

        base.OnModelCreating(mb);
    }
}

How to set a 0..* relationship in Entity Framework Code First?

2 Answers2

Linked