在MVC3中計數查詢數組時出錯

Question

我想要做的就是模擬一個隨機令牌，它將通過url從另一個系統發送。這等系統也將在數據庫中插入3個值：

• ID
• IP
• 當前時間

現在時，在另一個時間，客戶端訪問應用程序，它必須有與首次訪問系統相同的IP和ID，時間差必須在30分鐘以內，否則會話將不會被認證，並且機器將被限制併發送到錯誤頁面。

我有一個問題：

• 當我執行session[] sessionArray = a.ToArray();出現以下錯誤：

{"FUNCTION cgdimport.DiffMinutes does not exist"}

通過WiiMaxx作爲解釋：

no your ERROR isn't there your error is EntityFunctions.DiffMinutes(b.start, DateTime.Now). because your b doesnt contains a function called DiffMinutes()

所以，我想替代方案：

ar a = (from b in data.session 
where b.idsession == sessionid 
&& b.ip == clientip 
&& DateTime.Now <= b.start + new TimeSpan(0, 0, 30, 0) 
select b); 

但它給我下面的錯誤：

DbArithmeticExpression arguments must have a numeric common type.

而另：

var a = (from b in data.session 
          where b.idsession == sessionid 
          && b.ip == clientip 
          && DateTime.Now <= b.start.AddMinutes(30) 
          select b); 

但出現此錯誤：

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

public ActionResult SessionController() 
    { 
     var data = new cgdimportEntities(); 



     //Request sessionnid from the URL 
     if (!Request.QueryString["token"].IsEmpty() && Request.QueryString["token"] != null) 
     { 
      //Obtain client IP 
      string clientip = HttpContext.Request.UserHostAddress; 


      //Request sessionid from url 
      string sessionid = Request.QueryString["token"]; 
      //string sessionid = token; 

      //Dummy Test Insert 

      var sessionvar = new session {idsession = sessionid, ip = clientip, start = DateTime.Now}; 

      data.session.Add(sessionvar); 


      try { data.SaveChanges(); } 

      catch (DbEntityValidationException dbEx) 
       { 
       foreach (var validationErrors in dbEx.EntityValidationErrors) 
       { 
        foreach (var validationError in validationErrors.ValidationErrors) 
        { 
         Trace.TraceInformation("Class: {0}, Property: {1}, Error: {2}", validationErrors.Entry.Entity.GetType().FullName, 
            validationError.PropertyName, validationError.ErrorMessage); 
        } 
       } 
       } 

      //old code 
      //var a = (from b in data.session 
         //where b.idsession == sessionid 
         //&& b.ip == clientip 
         //&& EntityFunctions.DiffMinutes(b.start, DateTime.Now) < 30 
         //select b); 
      //old code 
      //var a = (from b in data.session 
         //where b.idsession == sessionid 
         //&& b.ip == clientip 
         //&& DateTime.Now <= b.start + new TimeSpan(0, 0, 30, 0) 
         //select b); 

      //new code 
       var a = (from b in data.session 
         where b.idsession == sessionid 
         && b.ip == clientip 
         && DateTime.Now <= b.start.AddMinutes(30) 
         select b); 


      int count = 0; 


      //ERROR HERE! ERROR HERE! 
      session[] sessionArray = a.ToArray(); 


      foreach (var i in sessionArray) 
      { 
       count++; 
      } 

      //if 0 rows are counted 
      if (count == 0) 
      { 
       Session["authenticated"] = "false"; 
       return RedirectToAction("Erro", "Login", new { erro = "No rows counted" }); 
      } 
      //Once all queries are verified, the user is authenticated 
      Session["authenticated"] = "true"; 
      return RedirectToAction("Painel", "Data"); 
     } 
      Session["authenticated"] = "false"; 
      return RedirectToAction("Erro", "Login", new { erro = "Query is null" }); 
    } 

Answer 1

因爲DateTime比較的一個參數是一個常數（對於查詢），你可以採取AddMinutes關閉查詢應刪除例外：

DateTime nowMinus30Minutes = DateTime.Now.AddMinutes(-30); 

var a = (from b in data.session 
     where b.idsession == sessionid 
      && b.ip == clientip 
      && nowMinus30Minutes <= b.start 
     select b); 

Answer 2

使用EntityFunctions添加分鐘

ar a = (from b in data.session 
where b.idsession == sessionid 
&& b.ip == clientip 
&& DateTime.Now <= System.Data.Objects.EntityFunctions.AddMinutes(b.start, 30) 
select b);