Which collection(s) to store groups of users?

Question

I want to make a collection that stores groups of users. A user can be a member of multiple groups, groups can be nested, a selection of groups should return a distinct IEnumerable<user> .

I could write this from scratch of course using the standard List<T>,Dictionary<T,U> etc collections, but is there a built-in collection that already exposes a lot of this behaviour?

Thanks!

Answer 1

I would have a thought a generic List<T> would work (where T is the class that holds your user).

Answer 2

I would do something like this:

using System;
using System.Collections.Generic;

class Program
{
    static void Main()
    {
     List<User> users = new List<User>
     {
      // use a List<T> to hold the users themselves
     };
    }
}

class Group
{
    public Group NestedGroup { get; set; }
}

class User
{
    // Store the groups in a HashSet<T> to keep
    // a distinct list.
    HashSet<Group> groups;

    public IEnumerable<Group> Groups
    {
     get { return groups; }
    }
}

Using a List<T> to hold the users themselves should be fine. Notice that the Groups property of the User type is exposed as an IEnumerable<Group> but is implemented internally as a HashSet<Group> to allow you to keep a distinct list as you wanted.

Answer 3

I would think that using List<T> would work for saving this information. You could have Groups with a parent group and a list of children groups, and each group containing a list of members, or something similar.

In terms of getting the IEnumerable<User> back out - this should be doable using Enumerable.SelectMany. Take a look at the MSDN sample there - they have a similar thing with pets and owners, where there are multiple elements spanning multiple collections.

Answer 4

It looks like you need a good old relational database. Throw in SQLite and go if you can.

Otherwise...I've sometimes done this via multiple Dictionaries and lists. You have a Dictionary of Groups, each group is a list. Then another Dictionary to store the users by a key of some sorts. Each user can exists in multiple groups that way.