How can i make this Linq Statement more sophisticated - linq

Question

After many hours of research i still can't get this query to shorten, but surely there is a way... My current query looks like so
decimal Cost = db.U_MBP
.Where(w => w.Model == ModelNumber)
.Select(s => s.Cost ?? 0)
.FirstOrDefault();
double Margin = db.U_MBP
.Where(w => w.Model == ModelNumber)
.Select(s => s.Margin ?? 0)
.FirstOrDefault();
decimal BasePrice = Cost / (decimal)Margin;
What I was initially trying to accomplish was an all in 1 linq statement, something like
decimal BasePrice = db.U_MBP
.Where(w => w.Model == ModelNumber)
.Select(s => s.Cost ?? 0 / (decimal)s.Margin ?? 0)
.FirstOrDefault();
But i cannot get over the cast error.
Casting to Decimal is not supported in LINQ to Entities queries, because the required precision and scale information cannot be inferred.
Can any of you help?
Answer with D's Help
decimal BasePrice = (decimal)(db.Utilities_ModelsBasePrices
.Where(w => w.Model == ModelNumber)
.Select(s => (s.Margin == null || s.Margin == 0) ? (double)0m :
((double)s.Cost) / (double)s.Margin)
.FirstOrDefault());

Answer 1

The problem is here:
.Select(s => s.Cost ?? 0 / (decimal)s.Margin ?? 0)
The ?? operator has lower precedence than the / operator, so it's effectively calculating:
.Select(s => s.Cost ?? (0 / (decimal)s.Margin) ?? 0)
which translates to
if (s.Cost == null)
if((0 / (decimal)s.Margin))== null
return 0;
else
return (0 / (decimal)s.Margin);
else
return s.Cost;
You need to add parens when using ?? and other operators:
decimal BasePrice = db.U_MBP
.Where(w => w.Model == ModelNumber)
.Select(s => (s.Cost ?? 0) / ((decimal)s.Margin ?? 0))
.FirstOrDefault();
However, you will get a divide-by-zero exception if s.Margin is null or 0. I would recommend:
decimal BasePrice = (decimal)(db.U_MBP
.Where(w => w.Model == ModelNumber)
.Select(s => (s.Margin == null || s.Margin == 0) ? 0.0 :
((double)s.Cost ?? 0) / s.Margin)
.FirstOrDefault());
Eric Lippert recently posted about the null coalescing precedence on his blog.