c＃linq分组依据-访问其他属性，选择新的

Question

I'm converting a grouped Type1 list in another Type2 list and I'm wondering how it is possible to define a property of Type2 object as a concatenation of other and just defined Type2 properties, inside select new from grouped items.

My code is the following:

List<Type1> list1 = GetList1();

List<Type2> list2 = (from r in list1
                    group r by new
                    {
                         r.Prop1,
                         r.Prop2,
                         r.Prop3
                    }
                    into groupedRequest
                     select new Type2()
                     {
                         Prop1 = groupedRequest.Key.Prop1,
                         Prop2 = GetProp2FromComplexOperation(groupedRequest.Key.Prop1),
                         Prop3 = Prop1 + Prop2 //<---- The name Prop1 does not exists in the current context
                     }).ToList<Type2>();

I'm not able to access to Prop1 and Prop2 inside new Type2() creation. Is it possible to do that in any manner?

I know is possible to calculate

Prop3 = groupedRequest.Key.Prop1 + GetProp2FromComplexOperation(groupedRequest.Key.Prop1);

but I want avoid to call again GetProp2FromComplexOperation.

Thanks in advance!

Answer 1

You can use let like this:

List<Type2> list2 = (from r in list1
                    group r by new
                    {
                         r.Prop1,
                         r.Prop2,
                         r.Prop3
                    }
                    into groupedRequest
                    let p1 = groupedRequest.Key.Prop1
                    let p2 = GetProp2FromComplexOperation(groupedRequest.Key.Prop1)
                     select new Type2()
                     {
                         Prop1 = p1,
                         Prop2 = p2,
                         Prop3 = p1 + p2
                     }).ToList<Type2>();