I have a classical Reader/Subscription/Newspaper schema, and I want that there's never 2 Subscriptions with the same pair of Reader x Newspaper.
To reassure this, I'm checking during the Subscription insertion whether there's already a Subcription with such keys. However a colleague has told me that I should move this validation outside of the Model, as it should only run SQL commands.
Is this how Models in MVC should behave? They should only contain SQL related commands?