How do I write a generic Save() method that handles single objects and collections?

Question

I have two generic save methods in a repository class:

public void Save<T>(T entity)
{
    _session.Save(entity);
}

public void Save<T>(IEnumerable<T> entities)
{
    foreach (var item in entities)
    {
        _session.Save(item);
    }
}

However, when I use Save(collection) (which infers the type automatically), it recognizes it as a T rather than IEnumerable<T> and tries to save it using the first method.

How do I write this save method(s) so that it can handle either case, without me having to explicitly provide the type?

Answer 1

Whjy bother with overloaded methods?, isn't better to do it like:

public void Save<T>(T entity)
{
    if (T is IEnumerable)
    {
         foreach (var item in entity)
              _session..Save(item);
    } else  {
        _session.Save(entity);
    }
}

Answer 2

You can't rely on type inference for this specific case. <T>(T) will satisfy any type, so the inference won't continue searching to find more specific constraints which still meet the signature.

Answer 3

You can use it like this also:

    public void Save<T>(T entity)
    {
        if (typeof(T).GetInterfaces().Contains(typeof(IEnumerable)))
        {
            SaveEnumerable(entity as IEnumerable);
        }
        else
        {
            _session.Save(entity);
        }
    }

    public void SaveEnumerable(IEnumerable entities)
    {
        foreach (var item in entities)
        {
            _session.Save(item);
        }
    }

Hope this helps!!

Answer 4

Put the type parameter at the class level on your repository instead of at the method level, this way the overload will not be ambiguous.

class Repo<T>
{
    public void Save(T entity)
    {
        _session.Save(entity);
    }

    public void Save(IEnumerable<T> entities)
    {
        foreach (var item in entities)
        {
            _session.Save(item);
        }
    }
}

You'd use it like this:

var repo = new Repo<Person>();

var p = new Person();
repo.Save(p);

var ps = new Person[] { p };
repo.Save(ps);