Question

I’ve just started working with Web API this week, and I’m struggling with something which I think should be quite simple, but haven’t been able to find the answer for yet. Perhaps I’m searching using the wrong terms.

One of the calls to the API passes through a GUID. I need to create a new entity (using Entity Framework) and set one of the relations to this newly passed in GUID. This GUID is the ID of a different entity in the database.

I’m struggling to attach the entity via the relation without fetching the whole entity too.

For example,

public void DoWork(IList<Guid> userGuids)
{
     Order order = new Order() // This is an entity
     {
         CreateDate = DateTime.Now,
         CreatedBy = "Me",
         Items = (from i in this.Model.Items
                      where i.Id == userGuid
                      select i).ToList<Item>();
     }

     Model.Orders.Add(order);
     Model.SaveAll();
}

In the above, I have to do a database call to attach the Item entities to the Order. Is there not a way around this? Seems very redundant to retrieve the whole entity objects when I only require their IDs (which I already have anyway!)!

Answer 1

One solution is stub entities as asked here: Create new EF object with foreign key reference without loading whole rereference object

Link to the source blog referenced: http://blogs.msdn.com/b/alexj/archive/2009/06/19/tip-26-how-to-avoid-database-queries-using-stub-entities.aspx

Snip from the blog – to be applied to your situation:

Category category = new Category { ID = 5};
ctx.AttachTo(“Categories”,category);

Product product = new Product {
 Name = “Bovril”,
 Category = category
};
ctx.AddToProducts(product);
ctx.SaveChanges();

This way (in the example) the Product is saved without ever loading the Category object.