Try this:
products.Select(x => new
{
Product = x,
AverageRating = x.Responses.Sum(x => x.FinalRate) /
x.Responses.Count()
});
The Sum
overload I am using is not implemented in all providers. If that's a problem for you, you can use this alternate version:
products.Select(x => new
{
Product = x,
AverageRating = x.Responses.Select(x => x.FinalRate)
.Sum() /
x.Responses.Count()
});
If there is no navigation property from product to its responses you should first try to fix that. If you can't you can use this version:
products.Join(responses, x => x.Id, x => x.ProductId,
(p, r) => new { Product = p, Response = r })
.GroupBy(x => x.Product)
.Select(g => new { Product = g.Key,
AverageRating = g.Select(x => x.Response.FinalRate)
.Sum() /
g.Count()
});
Assuming FinalRate
is an int
, both methods will calculate the average rating with an int, i.e. there will be no 4.5 rating. And there will be no rounding, i.e. an actual average rating of 4.9 will result in 4. You can fix that by casting one of the operands of the division to double
.
Another problem is the case with no ratings so far. The code above will result in an exception in this case. If that's a problem for you, you can change the calculation to this:
AverageRating = g.Count() == 0
? 0
: g.Select(x => (double)x.Response.FinalRate).Sum() / g.Count()