Question

我想从数据库IEnumerable<T>和'Select'方法中使用函数返回string值。但我总是回到

'方法无法转换为商店表达式'

错误。

我已经看过Stack Overflow关于错误的所有帖子'LINQ to Entities无法识别方法....并且此方法无法转换为商店表达式“

我发现解决此错误的唯一方法是在查询运行后应用该函数。

void Main()
{
   int eventId = 17;

   IEnumerable<OccurrenceDropDownList> model = Occurrences.Select (s => new OccurrenceDropDownList
      {
         OccurrenceId = s.OccurrenceId,
         Name = s.Name
      })
      .AsEnumerable()
      .Select(m => new OccurrenceDropDownList
          {
             OccurrenceId = m.OccurrenceId,
             Name = m.Name,
             Selected = setSelected(m.OccurrenceId, eventId)
          }).AsEnumerable();

    foreach(var item in model)
    {
       Console.WriteLine(item.Name + " - id : " + item.OccurrenceId + " " + item.Selected); 
    }
}


public class OccurrenceDropDownList
{
        public int OccurrenceId { get; set; }
        public string Name { get; set; }
        public string Selected { get; set; }
}

static string setSelected(int occurrence, int selectedid){
    if(occurrence == selectedid){
        return "selected";
    }
    return "";
}

有没有办法将该函数作为第一个查询的结果应用？

Answer 1

应该更简单：

int eventId = 17;
IEnumerable<OccurrenceDropDownList> model = Occurrences
   .Select(s => new OccurrenceDropDownList
                    {
                       OccurrenceId = s.OccurrenceId,
                       Name = s.Name,
                       //magic ternary if
                       Selected = (eventId == s.OccurrenceId) ? "selected" : String.Empty
                    });

这就是全部。我使用了应该转换为SQL的三元if运算符。

Linq to Sql使用函数设置值

1 个答案: