Entity Framework Execute Expression - linq

Question

Here is simplified code
from oi in orderItems
group oiGrouped by ...
into orderItemsGroupedBySomething
select new
{
Key = orderItemsGroupedBySomething.Key,
Revenue = /*Here is some code that I want to extract to separate method, for example*/
orderItemsGroupedBySomething.Sum(x => x.UnitPrice * x.Quantity)
}
Actually it's more complex in my case. But I think it doesn't matter. I'm not able to extract to simple method calculation of orderItemsGroupedBySomething.Sum(x => x.UnitPrice * x.Quantity) because it's not known method for EntityFramework. I tried put it to expression but I get error "The LINQ expression node type 'Invoke' is not supported in LINQ to Entities." I compiled expression before use it in query, I think therefore I get error. How can I solve this problem?

Answer 1

I don't know how generic you need it to be, but something like this should work:
void Main()
{
OrderItems.GroupBy(oi => oi.SomeProp).Select(GetExpression());
}
public Expression<Func<IGrouping<KeyType, OrderItem>, dynamic>> GetExpression()
{
return (ig) => new { Key = ig.Key, Revenue = ig.Sum(x => x.UnitPrice * x.Quantity) };
}
edit: In the case of a grouping, I would probably return a Tuple in stead of an anonymous type.

Answer 2

I added method that return expression
public Expression<Func<OrderItem, decimal>> GetExpression()
{
return x => x.UnitPrice*x.Quantity;
}
Then I tried
from oi in orderItems
group oiGrouped by ...
into orderItemsGroupedBySomething
select new
{
Key = orderItemsGroupedBySomething.Key,
Revenue = orderItemsGroupedBySomething.Sum(GetExpression())
}
But it doesn't work such as with #LorentzVedeler answer. Because orderItemsGroupedBySomething is of type IGrouping that don't have Sum method with param of type Expression. Therefore I tried
orderItemsGroupedBySomething.AsQueryable.Sum(GetExpression())
But it causes Internal .NET Framework Data Provider error 1025. The issue was that I invoked method GetExpression() in linq. To solve this problem I put expression to local variable. The result
var expression = GetExpression();
from oi in orderItems
group oiGrouped by ...
into orderItemsGroupedBySomething
select new
{
Key = orderItemsGroupedBySomething.Key,
Revenue = orderItemsGroupedBySomething.AsQueryable.Sum(expression)
}