c# Linq Compound Froms

I’m a bit embarrassed to admit this, but even after using linq in it’s various form for a couple of years now, I hadn’t really ever noticed compound from expressions e.g.

   1:  public void Linq16()

   2:  {

   3:      List<Customer> customers = GetCustomerList();

   4:   

   5:      var orders =

   6:          from c in customers

   7:          from o in c.Orders

   8:          where o.OrderDate >= new DateTime(1998, 1, 1)

   9:          select new { c.CustomerID, o.OrderID, o.OrderDate };

  10:   

  11:      ObjectDumper.Write(orders);

  12:  }

(from 101 LINQ samples)

Very handy for flattening an object hierarchy, etc. In the end though it’s just syntactic sugar over SelectMany (like a good deal of many LINQ functions). Anyway, another tool in the belt.

Shaping Entity Framework Results

In order to comply with an interface I needed to write code similar to the following:
<br />return (from ActionRule ar in db.ActionRuleSet.Include("ConditionExpression")<br /> select new ActionRuleDataDTO() <br /> { <br /> Expresions = (from ConditionExpression ce in ar.ConditionExpression<br /> select new RuleExpressionDTO()<br /> {<br /> Type = ce.Operator,<br /> BoolOperator = ce.NextExpressionOperator<br /> }).ToArray() <br /> }).ToArray(); <br /> Which results in:
LINQ to Entities does not recognize the method 'EhrAdmin.Services.MSSQL.DTO.RuleExpressionDTO[] ToArray[RuleExpressionDTO](System.Collections.Generic.IEnumerable`1[EhrAdmin.Services.MSSQL.DTO.RuleExpressionDTO])' method, and this method cannot be translated into a store expression.
I'll revisit this when i get a chance but the fix at the moment is to convert ObjectQuery<actionrule> to List<actionrule> using the ToList() method.