Question

How to convert following code to method operator:

var myOrders = from c in customers
               where c.Field<string>("Region") == "WA"
               from o in orders
               where c.Field<string>("CustomerID") == o.Field<string>("CustomerID")
               && (DateTime)o["OrderDate"] >= cutoffDate
               select new { 
                  CustomerID = c.Field<string>("CustomerID"), 
                  OrderID = o.Field<int>("OrderID") 
               };

———or———-

 var myOrders = from c in customers
               where c.Region == "WA"
               from o in orders
               where c.CustomerID == o.CustomerID
               && o.OrderDate >= cutoffDate
               select new { 
                  CustomerID = c.CustomerID, 
                  OrderID = o.OrderID 
               };

same code in object form

Answer 1

I’d actually rewrite this as a join – probably via intermediate variables:

var washingtonCustomers = customers.Where(c => c.Field<string>("Region") == "WA");
var recentOrders = orders.Where(o => (DateTime)o["OrderDate"] >= cutoffDate);

var query = washingtonCustomers.Join(recentOrders, 
                 c => c.Field<string>("CustomerID"),
                 o => o.Field<string>("CustomerID"),
                 (c, o) => new { 
                     CustomerID = c.Field<string>("CustomerID"), 
                     OrderID = o.Field<int>("OrderID") 
                 });