使用lambda和Entity Framework的.SELECT语句

Question

I am struggling here in using .SELECT statement.

Here a snippet of my code;

var payoutsPerLocation = locations.Select(l => l.Payouts);

foreach (var payouts in payoutsPerLocation)
{
    Console.WriteLine(payouts.Sum(pos=>pos.Amount));
}

Where in location is a list, and one location has one or more payout. I want to get all the payouts.

The above code's result is below

0
0
0
0
0
0

It should be the sum of the amount of payouts per location. It seems like I don't get any records of payout. But when I tried using the code below (for testing if I am getting payout);

var payoutsPerLocation = locations.FirstOrDefault().Payouts;

foreach (var payout in payoutsPerLocation)
{
    Console.WriteLine(payout.Amout);
}

There is a payout for that location. What do you guys think I am doing wrong here?

Any help is appreciated.

Answer 1

I don't know why it's giving you zeros, but you shouldn't evaluate Linq expressions inside a foreach loop anyway. It causes too many round-trips to the database. Try this:

var sumPerLocation = locations.Select(l => l.Payouts.Sum(p => p.Amount));
foreach (var sum in sumPerLocation)
{
    Console.WriteLine(sum);
}