LINQ to Entities不识别该方法的系统Linq IQueryable[副本]

当我试图在子选择中调用我的存储库时,出现了这个错误。

 IGrpTextRepository rep = new GrpTextRepository();

        var query = new DetailViewModel
        {
            ViewDet = (from gh in _db.Grp
                       select new MultiDetailViewModel
                       {
                           Header = gh,
                           Txts = rep.FindAllLangTxtById(gh.GrpID)

                       }).ToList(),
            Lang = _db.Language.ToList(),

        };

我的界面是

 public interface IGrpTextRepository
{
    IQueryable<GrpText> FindAllLangTxtById(int GrpID);
}

public class GrpTextRepository : IGrpTextRepository
{
    DBEntities db = new DBEntities();

    public IQueryable<GrpText> FindAllLangTxtById(int GrpID)
    {
        return (from lang in db.Language
               join gtxts in db.GrpText on lang.LangID equals gtxts.LangID into jointxt
               from fintxt in jointxt.DefaultIfEmpty()
               where fintxt.GrpID == GrpID
               select fintxt);
    }


}

这是完整的错误信息