c# – LINQ to Entities无法识别方法’System.Linq.IQueryable

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);
    }


}

这是完整的错误消息

System.NotSupportedException：LINQ to Entities无法识别方法’System.Linq.IQueryable`1 [aaa.Models.GrpText] FindAllLangTxtById(Int32)’方法,并且此方法无法转换为商店表达式.