How to combine these LINQ queries and will it be 3X faster?

Question

I've been optimizing some badly written LINQ queries. I used to iterate over an IQueryable "Items" which was causing the queryable to go to list and slow things down a bit (return all records). I ended up with this code which was noticeably faster:

  IQueryable<InventoryItem> Items;
 
      Items = from m in _context.Inventory.Where(m => m.Removed == 0)
              select m;
      //  various filtering happens...

     int ItemsCount = await Items.CountAsync();
     int TotalQTY = await Items.SumAsync(s=>s.IntegerQuantity);
     decimal TotalPrice = await Items.SumAsync(s => s.IntegerQuantity * s.ApproximateCost);
            
     InventoryTotals inventoryTotals = new()
     {
         TotalQuantity = TotalQTY,
         NumberOfItems = ItemsCount,
         TotalApproximatePrice = TotalPrice
     };

My question is how to combine those three LINQ statements, and if I do, will it be faster? 3 times the speed?

Answer 1

You can try doing the sums in one query using GoupBy:

var results = Items.GroupBy(s => 1)
     .Select(g => new InventoryTotals {
        NumberOfItems = g.Count(),
        TotalQuantity = g.Sum(s=>s.IntegerQuantity),
        TotalApproximatePrice = g.Sum(s => s.IntegerQuantity * s.ApproximateCost)
      })
    .First();