C# 实体框架中的左join和case子句LINQ

我需要做一个左连接，并使用select操作符。 我的LINQ basic是这样的，可以工作：

resultado.Dados =
    (
        from a in db.AgendaHorario
        join b in db.Agenda on a.AgendaID equals b.AgendaID
        join c in db.Profissional on a.ProfissionalID equals c.ProfissionalID into d
        from e in d.DefaultIfEmpty()                        
        select new
        {
            id = a.AgendaHorarioID,
            Medico = e.Identificacao     
        });

但我必须添加一个新字段，并对其进行格式化，然后我的LINQ如下所示：

resultado.Dados =
  (
    from a in db.AgendaHorario
    join b in db.Agenda on a.AgendaID equals b.AgendaID
    join c in db.Profissional on a.ProfissionalID equals c.ProfissionalID into d
    from e in d.DefaultIfEmpty()                        
    select new
    {
        id = a.AgendaHorarioID,
        Medico = e.Identificacao,
        start = a.Horario.ToString("yyyy-MM-dd HH:mm:ss")            
    }
  );

发生以下错误：

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

如果在

db.AgendaHorario.ToList（）

和

db.Agenda.ToList（）

和

db.Profissional.ToList（）

中添加ToList（）或AsEnumerable（）

Object reference not set to an instance of an object.

---

我应该怎么做才能使大小写、字段和格式化字段具有左连接？尝试在变量中设置字符串，然后将其分配给查询，如下所示：

resultado.Dados =
  (
    from a in db.AgendaHorario
    join b in db.Agenda on a.AgendaID equals b.AgendaID
    join c in db.Profissional on a.ProfissionalID equals c.ProfissionalID into d
    from e in d.DefaultIfEmpty()                        
    select new
    {
        id = a.AgendaHorarioID,
        Medico = e.Identificacao,
        start = a.Horario.ToString("yyyy-MM-dd HH:mm:ss")            
    }
  );

试试这个：

resultado.Dados =
(
    from a in db.AgendaHorario
    join b in db.Agenda on a.AgendaID equals b.AgendaID
    join c in db.Profissional on a.ProfissionalID equals c.ProfissionalID into d
    from e in d.DefaultIfEmpty()                        
    select new
    {
        id = a.AgendaHorarioID,
        Medico = e.Identificacao,
        start = a.Horario
    }).AsEnumerable().Select(x => new
    {
        id = x.id,
        Medico = x.Medico,
        start = x.start.ToString("yyyy-MM-dd HH:mm:ss")            
    }
);

---

对不起，我不明白。您传递的代码无效。上面代码的第一行需要由db.AgendaHorario提供，因此您需要修改该行以获得值