C# Access the Properties of a Generic Object

Question

I have a method that counts the number of Contacts each Supplier, Customer and Manufacturer has (this is a scenario to try make explaining easier!)

The models are all created by Linq to SQL classes. Each Supplier, Customer and Manufacturer may have one or more Contacts

public int CountContacts<TModel>(TModel entity) where TModel : class
{
    return entity.Contacts.Count();
}

The above of course doesnt work, because the 'entity' is generic and doesnt know whether it has the property 'Contacts'. Can someone help with how to achieve this?

Answer 1

An easy way would be to attach an interface to the classes being implemented in the generic.

public int CountContacts<TModel>(TModel entity) where TModel : IContacts


interface IContacts
{
   IList<Contact> Contacts {get;} //list,Ilist,ienumerable
}

Answer 2

One way to impose a contract where Suppliers, Customers and Manufactors must contain a Contacts property is with interfaces. Make each entity implement one interface that contains the Contacts property:

interface IContactable
{
   IEnumerable<Contact> Contacts {get;}
}


public int CountContacts<TModel>(TModel entity) where TModel : class, IContactable
{
    return entity.Contacts.Count();
}