LINQ Query with both CASE statement and SUM function

Question

I\'m struggling to find an example of how to return a conditional sum using a LINQ query or LAMBDA. I\'ve written both independently but combining the CASE with SUM is vexing.

Answer 1

answer does not wrong but does not generate optimize query. better answer is:

using (var context = new NorthwindEntities())
{
    DateTime volumn1Date = DateTime.Today.AddDays(-1);
    DateTime volumn7Date = DateTime.Today.AddDays(-7);
    DateTime volumn30Date = DateTime.Today.AddDays(-30);

var query = from o in context.Order_Details
                group o by o.Product.ProductName into g
                select new
                {
                    ProductName = g.Key,
                    Volume1Day = g.Sum(d => d.Order.OrderDate.Value <= volumn1Date ? (Int32?) d.Quantity : 0),
                    Volume7Day = g.Sum(d => d.Order.OrderDate.Value <= volumn7Date ? (Int32?) d.Quantity : 0),
                    Volume30Day = g.Sum(d => d.Order.OrderDate.Value <= volumn30Date ? (Int32?) d.Quantity : 0)
                };

    var list = query.ToList();
}