C# Interface Return Types

I have a couple of interfaces, IOrganisations and IPeople.

If I want to return a list of people associated with an organisation, which interface do I 开发者_运维知识库create this in?

The results are based on an organisation, yet I'm returning a list of people

Do it on IOrganisation(and have IPeople as the return type).

Something like this:

interface IOrganisation {
    IList<IPeople> GetPeople();
}

This is because the people of an organisation is a property of the organisation, not of the people.

That sounds like it should be on IOrganization - that's what you'll call it on, after all. What you have is the organization, you want the list of people - you can't start fromt the list of people, so it must be part of the IOrganization interface.

I find it strange to have plural interface names to start with - I'd expect IOrganization for a single organization, and IPerson for a single person.

public interface IOrganization {
    IList<IPerson> GetPeople();
}

First of all, your should probably not have pluralized interface names. So call them IOrganization and IPerson and then on your IOrganisation interface you might have a method called:

IEnumerable<IPerson> GetPeople()

Which belongs to which?

It seems to me that iOrganisation.People would be a list of people ( is your "IPeople" interface representing a list of people or a single person? ) belonging to the organisation. Likewise you might have an IPeople.Organisations that lists all organisations that a person belongs to. Both will probably have a different underlying mechanism - maybe calling the same lookup table - it doesn't matter to the person calling the code.

If you think of an organization as a collection containing people, then it's intuitive to put that in IOrganization. It would look like this:

interface IOrganization
{
  IList<IPeople> Members { get; }
}