entity-framework - 无法将 dbSet 隐式转换为 ObjectQuery

Question

那是我的代码，它不能这样工作，请帮助我！！！

public class BL: IBL, IDisposable
{

    private TradeSoftDBEntities entities;

    public List<Roles> TakeRoles()
    {

        if (entities == null) 
            entities = new TradeSoftDBEntities();

        ObjectQuery<Roles> roles = entities.Rolis;

        roles.MergeOption = MergeOption.NoTracking;