Exposing/Passing a LINQ expression to be used on an private list

Question

I have an private List and I want to expose the ability to query the List and return a new List with new cloned items. I can pass in delegates for filtering and sorting, which works fine, but being able to use Linq expressions would be much more elegant.

I've added an simplified example of what I'm trying to do, which might help as I don't think I've explained what I want to do very well.

public class Repository
{
    private List<SomeModel> _models;
    private object _lock;

    public List<SomeModel> GetModels(Func<SomeModel, bool> predicate)
    {
        List<SomeModel> models;
        lock (_lock)
        {
            models = _models.Where(m => predicate(m))
                            .Select(m => new SomeModel(m))
                            .ToList();
        }
        return models;
    }
}

Answer 1

Why does your code involve locking? Assuming your "SomeModel" class has a copy constructor as your example suggests, this should work:

public List<SomeModel> GetModels(Predicate<SomeModel> predicate)
{
    return _models.Where(m => predicate(m))
                  .Select(m => new SomeModel(m))
                  .ToList();
}

Answer 2

You could expose the private collection as an iterator block by doing something like this:

public IEnumerable<Model> Models
{
    get
    {
        foreach (Model mod in this._models)
            yield return new Model(mod);

        // equivalent to:
        // return _models.Select(m => new Model(m));
        // as per Jon's comment
    }
}

Which would give you the ability to then write queries against it like any other IEnumerable datasource.