LINQ - Nested Query

Question

I have a SQL Statement that I am trying to convert to a LINQ query. I need to do this because I can\'t edit my database :(. Regardless, I have a SQL Statement that looks like th

Answer 1

The answer by BrokenGlass did not work for me when using Linq to Entities and resulted in an error stating "Unable to create a constant value of type 'MyEntity'. Only primitive types or enumeration types are supported in this context."

In order to overcome this I used the following:

var results = from x in context.MyEntities
              join po in context.PurchaseOrders on x.CustomerID equals po.CustomerID into purchaseOrders
              select new Customer() 
              { 
                CustomerID = x.CustomerID, 
                FirstName = x.FirstName, 
                LastName = x.LastName, 
                Gender = x.Gender, 
                BirthMonth = x.BirthMonth,
                TotalPurchases = purchaseOrders.Count()
              };

Answer 2

You can just nest the Linq to Entities query as well:

var results = from x in context.MyEntities 
              select new Customer() 
              { 
                CustomerID = x.CustomerID, 
                FirstName = x.FirstName, 
                LastName = x.LastName, 
                Gender = x.Gender, 
                BirthMonth = x.BirthMonth,
                TotalPurchases = context.PurchaseOrders
                                        .Where(po=>po.CustomerId == x.CustomerId)
                                        .Count()
              };

Answer 3

Just do a count off of the navigation property of "PurchaseOrders" that I assume is on the Customer entity.

TotalPurchases = x.PurchaseOrders.Count()