Question

I have the following for each loop to get sum of all child objects. Is there a better way using LINQ?

Purchase p1 = db.Purchases.FirstOrDefault(p => p.PurchaseId == 1);

int total = 0;
foreach (SellingItem item in p1.SellingItems)
{ 
   total = total + Convert.ToInt32(item.Price);
}

REFERENCE:

1. How to get the sum of the volume of highest and lowest priced items in linq

2. Using the ALL operator in linq to filter child items of EntitySet

Answer 1

Sounds like you just want:

// Any reason for FirstOrDefault rather than SingleOrDefault?
var purchase = db.Purchases.FirstOrDefault(p => p.PurchaseId == 1);

if (purchase != null)
{
    var total = purchase.SellingItems
                        .Sum(x => Convert.ToInt32(x.Price));
    ...
}
// TODO: Work out what to do if there aren't any such purchases

Why do you need the conversion of the price though? What type is Price, and why isn’t it already the right type? (And does that really want to be int rather than decimal?)