将Datetime转换为字符串实体框架

Question

I Have the following Method:

public List<REP_MEDIDORDISPLAY> GetAllMedidoresDisplay()
{          
    return ent.TB_MEDIDOR.Select(x => new REP_MEDIDORDISPLAY
    {
            Data_TOI = x.Data_TOI,
            Elemento = x.Elemento,
            Fase = x.Fase,
            KdKe = x.KD_KE,
            N_Equipamento = x.Numero,
            Tensao = x.Tensao,
            Status =  x.TB_REVISAO.Count > 0 ? "Revisão": 
                      x.TB_CHECAGEM_INTERNA.Count > 0 ? "Checagem interna":
                      x.TB_MESACALIBRACAO.Count > 0 ? "Mesa de calibração":
                      x.TB_HIPOT.Count > 0 ? "Hipot":
                      x.TB_INSPECAO.Count > 0? "Inspeção" :
                      x.TB_AGENDAMENTO.FirstOrDefault(y => y.ID_Medidor == x.ID).Data_Agendamento.HasValue ?
                  --> Error here (x.TB_AGENDAMENTO.FirstOrDefault(y => y.ID_Medidor == x.ID).Data_Agendamento.Value.ToString()) :String.Empty 
    }).ToList<REP_MEDIDORDISPLAY>();
}

But it's firing the following error when I try to convert a DateTime to String:

LINQ to Entities does not recognize the method 'System.String ToString()' method, and this method cannot be translated into a store expression.

I hope you can help me guys, I need that value as string, I can't change that to datetime.

Answer 1

Entity Framework does not know how to execute ToString() method in SQL. So you should load the data by using ToList() and then translate into SelectListItem as:

return ent.TB_MEDIDOR.ToList().Select(x => new SelectListItem
{ 
    Data_TOI = x.Data_TOI,
    ...
    // can convert DateTime to String here
})
// Then you can select this as a REP_MEDIDORDISPLAY if you want
.Select(y => new REP_MEDIDORDISPLAY
{
   Data_TOI = y.x.Data_TOI,
   ...
});

Answer 2

Remember that entity framework is converting your linq query to SQL. The error message is quite clear, it doesn't recognize the .ToString() method.

You will have to retrieve the results using entity framework and then perform the needed DateTime to String conversions.