EF6+ UoW Decorator

ContextDecorator.cs

public abstract class ContextDecorator : IContext
{
    private readonly IContext _context;

    #region Constructor

    protected ContextDecorator(IContext context)
    {
        _context = context;
    }

    #endregion

    #region Implementation of IContext

    public virtual int SaveChanges()
    {
        return _context.SaveChanges();
    }

    public virtual IContextMapper<Account> Accounts
    {
        get { return _context.Accounts; }
    }

    #endregion

    #region Implementation of IDisposable

    public void Dispose()
    {
        _context.Dispose();
    }

    #endregion
}

UserDecorator.cs

public class UserDecorator : ContextDecorator
{
    private readonly long _accountId;

    #region Constructor

    public UserDecorator(IContext context, long accountId) : base(context)
    {
        _accountId = accountId;
    }

    #endregion

    #region Overrides of ContextDecorator

    public override IContextMapper<Account> Accounts
    {
        get { return base.Accounts.Where(x => x.Id == _accountId); }
    }

    #endregion
}