我收到以下例外

Question

淨，我正在開發一個.net應用程序。

我收到以下錯誤，我不知道什麼是錯我的代碼

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

這是我的代碼，其中的例外來了。

public List<ToureDeieselBean> loadDeiselListOnTourUpDownId(int tourUpDownId) 
    { 
     return (from p in context.tb_tourDiesel 
       where p.deleted == 0 
       where p.tourUpDownId == tourUpDownId 
       select new ToureDeieselBean 
       { 
        id = p.id, 
        qty =(float)p.qty, 
        ratePerlt = (float)p.ratePerlt, 
        createdBy = p.createdBy, 
        createdOn = p.createdOn==null?"":(p.createdOn).ToString(), 
        updatedBy = p.updatedBy, 
        updatedOn = p.updatedOn == null ? "" :(p.updatedOn).ToString(), 
        descrption=p.descrption, 
        deleted=Convert.ToBoolean(p.deleted) 
       }).ToList<ToureDeieselBean>(); 
    } 

Answer 1

您可以通過使用去除ToString和更長的三元運營商null coalescing operator：

public List<ToureDeieselBean> loadDeiselListOnTourUpDownId(int tourUpDownId) 
{ 
     return (from p in context.tb_tourDiesel 
       where p.deleted == 0 
       where p.tourUpDownId == tourUpDownId 
       select new ToureDeieselBean 
       { 
        id = p.id, 
        qty =(float)p.qty, 
        ratePerlt = (float)p.ratePerlt, 
        createdBy = p.createdBy, 
        createdOn = p.createdOn ?? "", 
        updatedBy = p.updatedBy, 
        updatedOn = p.updatedOn ?? "", 
        descrption=p.descrption, 
        deleted=Convert.ToBoolean(p.deleted) 
       }).ToList<ToureDeieselBean>(); 
} 

Answer 2

當你與EF LINQ查詢工作被翻譯成SQL，而當你在LINQ使用的此類方法沒有按在SQL中不存在這個異常。

這將工作：

var temp=(from p in context.tb_tourDiesel 
       where p.deleted == 0 
       where p.tourUpDownId == tourUpDownId).ToList<ToureDeieselBean>(); 

     return (from p in temp 
       select new ToureDeieselBean 
       { 
        id = p.id, 
        qty = (float)p.qty, 
        ratePerlt = (float)p.ratePerlt, 
        createdBy = p.createdBy, 
        createdOn = p.createdOn == null ? "" : (p.createdOn).ToString(), 
        updatedBy = p.updatedBy, 
        updatedOn = p.updatedOn == null ? "" : (p.updatedOn).ToString(), 
        descrption = p.descrption, 
        deleted = Convert.ToBoolean(p.deleted) 
       }).ToList();