C# : Extending Generic class

Question

partial class Repository<TEntity> : IRepository<TEntity> where TEntity : class
{
}

My generic repository implements a common set of methods for TEntity like

public TEntity Get(int id)
{
    return _context.Set<TEntity>()
        .Find(id);
}

public TEntity Get(Expression<Func<TEntity, bool>> predicate)
{
    return _context.Set<TEntity>()
}

which I can access like

Repository<User>().Get();

Many repositories does the same set of operation, so it is beneficial but now I want to extend Repository<User> to support some additional behavior.

partial class Repository<User> : IRepository<User> 
{
    public user DoMagicFunction()
    {
    }
}

so that I can use the repository like

Repository<User>().DoMagicFunction();

how can I extend the same generic class for Some Tentity to extend new behaviour instead of modifying it.

I could have done the same like creating another UserRepository to support new feature, but the accessor would become

UserRepository.DoMagicFunction();

but I want it to be like

Repository<User>().DoMagicFunction();

Answer 1

You can use an extension method:

public static class ExtensionMethods {

    public static User DoMagicFunction(this Repository<User> repository) {
        // some magic
        return null; //or another user
    } 

}

This will thus add the function in a syntactically nice way to Repository<User> objects.

In case you want to support it not only for Users, but for subclasses of Users as well, you can make the function generic:

public static class ExtensionMethods {

    public static TEntity DoMagicFunction<TEntity>(this Repository<TEntity> repository)
        where TEntity : User {
        // some magic
        return null; //or another TEntity
    } 

}