Linq查询-返回总和

Question

I am having trouble figuring out how to do something like the following. This is purely pseudocode:

decimal totalActiveCost = (from i in _context.KeyActives 
                           where i.Pk in (active1fk, active2fk, active3fk, active4fk, active5fk, keyActiveFk) 
                           select sum(i.Cost)...`

Then summing the i.Cost. So basically, I need to return the i.Cost for each "Active" - so, for example, say active1fk is 1, active2fk is 2, and so on. I need to get the Cost for each of these and sum them up.

Answer 1

You can have your active foreign keys in a List<T> like:

List<int> activeFks = new List<int> {1,2,3,4,5,};
var sum = (from i in _context.KeyActives
           where activeFks.Contains(i.PK)
           select i.Cost).Sum();

Or with a method syntax:

var sum = _context.KeyActives
          .Where(r=> activeFks.Contains(r.PK))
          .Sum(r=> r.Cost);

Answer 2

Something like this will work:

List<Int> ids = new List<int>();
ids.Add(1);
ids.Add(2);
    var result = _context.KeyActives.
                 Where(c => ids.Contains(c.id))
                .Sum(c => c.Cost);

Answer 3

var ids = new List<int> {active1fk, active2fk, active3fk, active4fk, active5fk, keyActiveFk};
var sum = (from i in _context.KeyActives
           where ids.Contains(i.Pk)
           select i).Sum(a=> a.Cost);