Question

I have successfully setup a simple mvc application that lists teams. I’m using Ninject to inject the appropriate repository depending on the controller (thanks to stack overflow ;). All looks good, except that the repository code looks exactly the same. And I know that’s wrong. So my TeamRepository has two classes (for now).

public class SwimTeamRepository : ITeamRepository<SwimTeam> 
{
    private readonly Table<SwimTeam> _teamTable;
    public SwimTeamRepository(string connectionString)
    {
        _teamTable = (new DataContext(connectionString).GetTable<SwimTeam>());
    }

    public IQueryable<SwimTeam> Team
    {
        get { return _teamTable; }
    }
}

public class SoccerTeamRepository : ITeamRepository<SoccerTeam>
{
    private readonly Table<SoccerTeam> _teamTable;
    public SoccerTeamRepository(string connectionString)
    {
        _teamTable = (new DataContext(connectionString).GetTable<SoccerTeam>());
    }

    public IQueryable<SoccerTeam> Team
    {
        get { return _teamTable; }
    }
}

They look exactly the same except for the Class and Table name, so clearly I need to re-factor this. What would be the best approach here? Singleton? Factory Method?

Thanks in advance!

Answer 1

You could use generics:

public interface ITeamRepository<T>
{
}

public class TeamRepository<TTeam> : ITeamRepository<TTeam>
    where TTeam : Team
{
    private readonly Table<TTeam> _teamTable;
    public TeamRepository(string connectionString)
    {
        _teamTable = (new DataContext(connectionString).GetTable<TTeam>());
    }

    public IQueryable<TTeam> Team
    {
        get { return _teamTable; }
    }
}

public class Team
{
}

public class SwimTeam : Team
{
}

Then use it like so…

public void MyMethod()
{
    var repository = new TeamRepository<SwimTeam>();
}

…and set up your IoC container w/ Ninject like so…

public class MyModule : NinjectModule
{
    public override void Load()
    {
        Bind<ITeamRepository<SwimTeam>>
            .To<TeamRepository<SwimTeam>>();
    }
}

public void MyMethod()
{    
    var repository = kernel.Get<ITeamRepository<SwimTeam>>();
}

If you want to get REAL generic and have a single repository for ALL of your mapped classes, you can do something like this:

public interface IRepository
{
    IQueryable<T> Get<T>() where T : class, new();
}

public class Repository : IRepository, IDisposable
{
    private DataContext _dataContext;
    public Repository(string connectionString)
    {
        _dataContext = new DataContext(connectionString);
    }

    public IQueryable<T> Get<T>()
        where T : class, new()
    {
        return _dataContext.GetTable<T>().AsQueryable();
    }

    public void Dispose()
    {
        if (_dataContext != null)
        {
            _dataContext.Dispose();
            _dataContext = null;
        }
    }
}

…which you could call like so (after setting up your Ninject container)…

using (var repository = kernel.Get<IRepository>())
{
    var swimTeam = repository.Get<SwimTeam>();
}

Since Ninject takes care of the life-cycle management of your objects, you don’t HAVE to wrap the repository in a using statement. In fact, you don’t want to use a using statement there at all if you plan to use the repository more than once within the scope of its lifetime. Ninject will automatically dispose of it when it’s life-cycle ends.

Here’s a good article by Rob Conery on using this kind of technique to reduce the friction of using different ORMs.

EDIT by keeg:

I Think

public class TeamRepository<TTeam> : ITeamRepository<TTeam> where TTeam : Team {}

Should be

public class TeamRepository<TTeam> : ITeamRepository<TTeam> where TTeam : class {}

Please correct if I’m wrong.