Is there any way to provide custom factory for .Net Framework creation Entities from EF4 ?

Question

There are a lot of posts about how cool POCO objects are and how Entity Framework 4 supports them. I decided to try it out with domain driven development oriented architecture and finished with domain entities that has dependencies from services. So far so good. Imagine my Products are POCO objects. When i query for objects like this:

NorthwindContext db = new NorthwindContext();
var products = db.Products.ToList();

EF creates instances of products for me.

Now I want to inject dependencies in my POCO objects (products) The only way I see is make some method within NorthwindContext that makes something like pseudo-code below:

public List<Product> GetProducts(){
    var products = database.Products.ToList();
    container.BuildUp(products); //inject dependencies
    return products;
}

But what if i want to make my repository to be more flexible like this:

public ObjectSet<Product> GetProducts() { ... }

So, I really need a factory to make it more lazy and linq friendly. Please help !

Answer 1

Are you looking for the yield keyword?

public IEnumerable<Product> GetProducts()
{
    foreach(var product in database.Products)
    {
        yield return container.BuildUp(product);
    }
}

-- 2nd Attempt:

public IEnumerable<Product> BuildUp(this IEnumerable<Product> source)
{
    foreach(var product in source)
    {
        yield return container.BuildUp(product);
    }
}

Usage:

database.Products.Where(p => blah).BuildUp();

Answer 2

The answer is you shouldn't inject services into your entities. The reasoning behind this answer can be find on Jimmy Bogard's blog, as well as on my own one.

There are many problems, including:

• confusion about what methods use the injected dependency
• different lifecycles of entities and services
• difficulties in testing