如何转换DropDownList项以检查linq查询？ [英] How to Convert DropDownList items to check in linq query?

问题描述

我在asp.net中有一个下拉列表控件，其中包含从今天到下一个60天的日期以及另一个下拉列表控件的时间。现在，当用户从下拉列表控件中选择日期时，我调用SelectedItemChanged的方法。我想从该数据库中检查该日期，以从另一个未保存在数据库中的下拉列表中获取时间。问题在于转换我无法将具有日期的下拉列表项转换为datetime，以便我可以检查用户在LINQ查询中选择的值或项。



我尝试过多次认为如下：

 DateTime date = Convert.ToDateTime（DropDownListDate.SelectedValue）; 
 
  var  selectedDate = 来自 d  in  datacontext.Appointment 
 其中 d.AppointmentDate == date 
  select  d; 

我也尝试在会话中存储选定的值，但它没有奏效。我也试过了

 DateTime date = DateTime.Parse（DropDownlistDate.SelectedValue）; 

但是效果并不好。我想转换下拉列表控件中的选定值，以便我可以使用它来检查数据库并获取相应的ans。请帮忙。非常感谢任何帮助。

解决方案

 var selectedDate = 来自 d   datacontext.Appointment 
 其中 d.AppointmentDate。包含（ date ）
 选择 d; 

您在评论中已经提到的错误，

Quote：

字符串未被识别为有效的DateTime。

表示您传递的字符串到 Convert.ToDateTime（参数）; 不是有效的dateTime对象。在编写可以转换为DateTime对象的字符串时，您需要考虑很多事情。



字符串的语法，月份和日期顺序， - 或 / 的用法也可能会提高这种错误。这并不意味着您的dateTime不是人类可理解的dateTime，而是意味着.NET框架不了解DateTime的格式。



例如如果你使用，

  //  你想写2014年11月12日，看起来公平吗？ 
 DateTime dateTime =  new  DateTime（ 12 ， 11 ，  2014 ）; 
  //  抛出错误 

要最大限度地减少此错误，您需要传递参数

  //   2014年，11个月和第12天。 
 DateTime dateTime =  new  DateTime（ 2014 ， 11 ， 12 ）; 

字符串相同的东西。在从String转换为DateTime时，您需要好好处理DateTime分隔符（/在.NET中使用），月份日序列等。本文档 [ ^ ]解释了这个概念。



传递字符串的示例代码是，

 DateTime dateTime = Convert.ToDateTime（  05/01/1996）; 
  //  转换为5/1/1996 12:00:00 AM  

阅读 this [ ^ ]我的文章，了解（一点点）深度的DateTime。

这样我已经转换来自DropDownList的日期并且工作正常。

 DateTime date = Convert.ToDateTime（DropDownListDate.SelectedValue.ToString（））; 

I have a dropdownlist control in asp.net which contains dates from today to next 60 days and another dropdownlist control for time. Now, when a user selects a date from the dropdownlist control I call a method of SelectedItemChanged. I want to check that date from that database to get the times from another dropdownlist which is not saved in database. The problem is in the conversion I am not able to convert the items of dropdownlist which has dates to datetime so that I can check the value or item which is selected by the user in LINQ query.

I have tried many thinks as below:

DateTime date = Convert.ToDateTime(DropDownListDate.SelectedValue);

var selectedDate = from d in datacontext.Appointment
                   where d.AppointmentDate == date
                   select d;

I also tried to store selected value in session but it didn't worked. I also tried the

DateTime date = DateTime.Parse(DropDownlistDate.SelectedValue);

but it didn't worked as well. I want to convert the selected value from the dropdownlist control so that I can use that to check in the database and get the appropriate ans. Please Help. Any help is really appreciated.

解决方案

var selectedDate = from d in datacontext.Appointment
                   where d.AppointmentDate.Contains( date)
                   select d;

The error that you've already mentioned in the comments,

Quote:

String was not recognized as a valid DateTime.

means that the String that you're passing to the Convert.ToDateTime(argument); is not a valid dateTime object. There are actually many things you need to consider while writing a string that can be converted to a DateTime object.

The syntax of the string, the month and date sequence, usage of - or / might also raise this sort of error. It doesn't mean that your dateTime is not a human understandable dateTime but it means that the .NET framework doesn't understand the format of your DateTime.

For example if you use,

// you wanted to write 12th november 2014, seems fair?
DateTime dateTime = new DateTime(12, 11, 2014);
// throws error

To minimize this error, you need to be passing the parameters as

// 2014 year, 11 month and 12th day.
DateTime dateTime = new DateTime(2014, 11, 12);

Same stuff for the strings. While converting from String to a DateTime, you need to take a good care of the DateTime seperator (/ is used in .NET), the Month year day sequence etc. This document[^] of MSDN explains this concept a little bit accurately.

A sample code for you to pass a string would be,

DateTime dateTime = Convert.ToDateTime("05/01/1996");
// converts to 5/1/1996 12:00:00 AM

Read this[^] article of mine to understand the DateTime in (a little bit) depth.

This way I have converted the date from DropDownList and is working fine.

DateTime date = Convert.ToDateTime(DropDownListDate.SelectedValue.ToString());

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