Linq All on empty collection

Question

I need to check if all definitions contains some specific data. It works fine except the case when GroupBy returns empty collection.

var exist = dbContext.De         


        

Answer 1

Here is another trick:

var exist = dbContext.Definitions
    .Where(x => propertyTypeIds.Contains(x.PropertyTypeId) && x.CountryId == countryId)
    .GroupBy(x => x.PropertyTypeId)
    .Min(some_condition ? (int?)1 : 0) == 1;

It utilizes the fact that the above Min method returns:

(A) null when the set is empty
(B) 0 if the condition is not satisfied for some element
(C) 1 if the condition is satisfied for all elements

so we simple check the result for (C) using the nullable value comparison rules.