Entity Framework - add to join with only foreign key values

Question

OK, I have 3 tables, call them:

Person

• PersonID
• Name

Store

• StoreID
• Name

PersonStore

• PersonID
• StoreID

Now, I have a form which allows you to add stores to a person. However, I am getting the store ID back from the form. I don't really want to do a query to get the store object from Entity Framework. I just want to add to the table using the StoreID and the Person object which I have.

Answer 1

By default in EF this join table won't appear as an entity instead you'll get a many to many relationship which will show up as two navigation properties

i.e.

Person.Stores
Store.People

If you want to build a many to many relationship without retrieving the entities then attaching stub entities is the best way.

var person = // you already have the person
var store = new Store{StoreID = 5} // you know the storeID

ctx.AttachTo("Stores", store);
ctx.AttachTo("People", person); // assuming the person isn't already attached
person.Stores.Add(store);
ctx.SaveChanges();

The only problem with this code is it will fail if the relationship already exists, so you need to be sure you are creating a new relationship

For more on using Stub entities like this check out my post. Hope this helps.

Alex

Edit from OP:

Since I am using EF4, I used the following code to remove the string from the attach (thanks to tip 13 from the link).

var person = // you already have the person
var store = new Store{StoreID = 5} // you know the storeID

ctx.Stores.Attach(store);
person.Stores.Add(store);
ctx.SaveChanges();