Entity Framework One-to-Many with Default

Question

I\'m trying to do a one-to-many relationship in Entity Framework where one of the many items is optionally designated as default.

public class SomeEntity
{
          


        

Answer 1

That is a bit untypical 'setup' (and it's usually designated via some 'flag' on the item - but I can possibly see a need for something similar), and relating one item to the same parent twice.

However, this should work...

modelBuilder.Entity<SomeEntity>()
    .HasOptional(x => x.DefaultItem)
    .WithOptionalPrincipal() // x => x.DefaultForEntity)
    .WillCascadeOnDelete(false);
...
// public SomeEntity DefaultForEntity { get; set; } // optional

...and use it like:

var item = new Item { ItemName = "Default1", };
db.SomeEntities.Add(new SomeEntity { DefaultItem = item, Items = new[]
{
    item,
    new Item{ ItemName = "Item1", },
    new Item{ ItemName = "Item2", },
    new Item{ ItemName = "Item3", },
    new Item{ ItemName = "Item4", },
}
});
db.SaveChanges();