Question

I have the following Product class:

public class Product
{
    public string Name { get; set; }
    public float Price { get; set; }     
    public int? CategoryId { get; set; }
}

Now I have to count how many Product I have for each CategoryId and place them in a Dictionary<int, int>. Therefore:

IQueryable<Product> products = _productServices.GetAll(); //return IQueryable<Product>

Dictionary<int, int> productDict =  products.ToList()
                                            .GroupBy(p => p.CategoryId)
                                            .ToDictionary(pgroup => pgroup.key, pgroup => pgroup.Count());

The problem is that I obtain a Dictionary<int?, int> from the ToDictionary(). Even if I pre-filter the null values by placing Where(p => p.CategoryId != null) I do not change the type of CategoryId to int. I also tried to create and anonymous type:

products.ToList()
        .GroupBy(p => p.CategoryId)
        .Select(p => new { p.key ?? -1, p.Count() }  
        .ToDictionary(pgroup => pgroup.key, pgroup => pgroup);

But it gives an Invalid anonymous type member declarator error. I also tried to remove the ToList() but no luck. I google it a bit and I haven’t found anybody having this issue, although I think this situation might be frequent, especially when working with EF and databases. Anybody has a solution?

Answer 1

That’s because CategoryId is a nullable. So you need to select it’s Value property first:

products.ToList()
        .Where(p => p.CategoryId.HasValue)
        .Select(p => p.CategoryId.Value)
        .GroupBy(i => i)
        .ToDictionary(g => g.Key, g => g.Count());