Question

I have a simple data model and I am using EF4.1 code first (but the problem seems to be relevant to any EF4 approach) as an ORM to store and retrieve data.
The model looks somewhat like:

public class Customer
{
    public int CustomerId { get; set; }
    public string Name { get; set; }
    public virtual List<Product> Products { get; set; }
}

public class Product
{
    public int ProductId { get; set; }
    public string Name { get; set; }
    public virtual ICollection<Event> Events { get; set; }
    public virtual ICollection<Customer> Customers { get; set; }
}

public class Event
{
    public int EventId { get; set; }
    public string Name { get; set; }
    public virtual List<Product> Products { get; set; }
}

So the entity relationships are like:

Customer —– Product —– Event

An event affects N Products (eg. a raise in price or a deal on a product)
Each Customer has N Products belonging to him.

Now for every Event in the database I would like to get a set (note non duplicate entries) of Customers affected by this Event. A customer is affected by the event if he has at least one product affected by the event.

The naive implementation would be:

foreach (var ev in context.Events)
{
  foreach(var product in ev.Products)
  {
    //Check for customers with this product and add them to the list of affected customers
  }
}

But this seems like an anti-pattern. The question is:
How to write a query to solve this problem in a more effective manner? (maybe linq, but even native SQL would help)?

Answer 1

You might be looking for a query like this:

var query = from ev in context.Events
            select new
            {
              Event = ev,
              AffectedCustomers = (from pr in ev.Products
                                   from cu in pr.Customers
                                   select cu).Distinct()
            };