相关疑难解决方法(0)

如何使用linq将字符串转换为日期时间到实体....

我有以下查询,其中visit_date列数据类型是字符串...

var memberl = from v in abc.visits
              join m in abc.members on v.member_Id equals m.member_Id
              where Convert.ToDateTime(v.visit_Date) >= startdate && 
                    Convert.ToDateTime(v.visit_Date) <= enddate
              group m by new { m.member_Firstname, 
                               m.member_Lastname, m.member_Id } into g
              orderby g.Count()
              select new
              {
                  numVisits = g.Count(),
                  firstname = g.Key.member_Firstname,
                  lastname = g.Key.member_Lastname
              };

不幸的是我无法改变架构......

我有错误:

linq to entites does not recognise Convert.ToDatetime method

是否有任何可能的解决方案将字符串转换为Datetime？

更新的代码:

根据要求我更新了我的问题

 var data = (from v in abc.visits
                  join m in abc.members on v.member_Id equals …

我想将字符串值转换为日期时间

类

public class demoDate
{
    public DateTime DueDate;
    public int OrderReportID;

    public DateTime _DueDate 
    { 
        get { return DueDate; } 
        set { DueDate = value; } 
    }

    public int _OrderReportID 
    { 
        get { return OrderReportID; } 
        set { OrderReportID = value;} 
    }
}

询问

var DateQuery = (from o in db.Order_Reports
                 select new demoDate {
                    DueDate = System.DateTime.Parse(o.ReportDueDateTime), 
                    OrderReportID = o.OrderReportID
                 }).ToList();

此编码显示以下错误

LINQ to Entities无法识别方法'System.DateTime Parse(System.String)'方法,并且此方法无法转换为存储表达式.

我必须使用"convert to datetime"方法来比较日期时间与参考月份和年份,如下所示

var res =  db.Table1
//other tables, and where conditions
.Select(x => new MyObj
{
      //...
      Imp = x.MyTable.FirstOrDefault(y => y.date_val >= System.Data.Entity.DbFunctions.AddMonths(Convert.ToDateTime("01/" + x.month + "/" + x.year), 1))).Description
})

我知道Convert.ToDateTime无法从提供者的sql中翻译,我需要一个想法来做那个查询.

更新:我不会在转换之前实现查询,因为这显然意味着获取所有记录.