Linq查询日期错误。 [英] Linq query date error.

问题描述

我目前在以下where子句代码中的date属性上收到一个编译错误：



错误：

  string  ' 不包含' UploadDate ' 的定义，并且没有扩展名方法' UploadDate ' 接受类型'  string  ' （您是否缺少using指令或程序集引用？） 

  public  HttpResponseMessage获取（日期时间？日期）
 {
 如果（User.IsInRole（  admin））
 {
  //   IEnumerable< data_qy> data_queries;  
 
 DateTime昨天= DateTime.Today.AddBusinessDays（-4）; 
 
  var  query =（ from  c  in  db.data_qy 
 其中​​ c.UploadDate ==昨天&& 
 c.Cover ==   perst 
 选择（c .Name））。OrderByDescending（a = >  a。   UploadDate ）。Distinct（）; 
 
  var  data = query.ToList（）; 
 
  if （！data.Any（））
 {
  var  message =  string  .Format（ 没有找到数据）; 
  return  Request.CreateErrorResponse（HttpStatusCode.NotFound，message）; 
 
} 
 

我正在尝试查询数据，其中name属性仅与where子句过滤器一起显示。



任何指南都非常感谢。

谢谢

解决方案

  var 查询=（ from  c  in  db.data_qy 
 其中 c.UploadDate ==昨天&& c.Cover ==   perst 
 选择（c.Name））。OrderByDescending（a = >  a.UploadDate ）.Distinct（）; 

在这里，您选择 c.Name 因此你的 a 不再是 data_qy 类型，它变成字符串。



试试这个：

  var  query =（ from  c  in  db.data_qy 
 其中 c.UploadDate ==昨天&& c.Cover ==   perst 
 选择（c））。OrderByDescending（a = >  a.UploadDate） .Distinct（）; 

即不选择 c.Name ，选择 c ，它应该可以工作。



编辑：



另外，我发现你只需要不同的名称 s，所以你可以得到它们：

  var  query =（ from  c  in  db.data_qy 
 其中 c.UploadDate ==昨天&& c.Cover ==   perst 
 选择（c））。OrderByDescending（a = >  a.UploadDate）
。选择（a = >  a.Name）.Distinct（）; 

因此您的'UploadDate'属性为null-able，你必须使用 c.UploadDate.Value 。

  var  query =（来自 c   db.data_qy 
 其中​​ c.UploadDate.Value ==昨天&& 
 c.Cover ==   perst 
 选择（c））。OrderByDescending（a = >  a.UploadDate.Value）.Distinct（ ）; 

I am currently getting a an compiling error on the date property in the where clause code below:

error:

string' does not contain a definition for 'UploadDate' and no extension method 'UploadDate' accepting a first argument of type 'string' could be found (are you missing a using directive or an assembly reference?)

public HttpResponseMessage Get(DateTime? date)
       {
           if (User.IsInRole("admin"))
          {
              //IEnumerable<data_qy> data_queries;

               DateTime yesterday = DateTime.Today.AddBusinessDays(-4);

               var query = (from c in db.data_qy
                           where c.UploadDate == yesterday &&
                                 c.Cover == "prest"
                           select (c.Name)).OrderByDescending(a => a.UploadDate).Distinct();

               var data = query.ToList();

               if (!data.Any())
               {
                  var message = string.Format("No data found");
                   return Request.CreateErrorResponse(HttpStatusCode.NotFound, message);

              }

I am trying to query data, where the name property is only displayed distinctly with the where clause filters.

Any guide would be very much appreciated.
Thanks

解决方案

var query = (from c in db.data_qy
           where c.UploadDate == yesterday && c.Cover == "prest"
           select (c.Name)).OrderByDescending(a => a.UploadDate).Distinct();

Here, you are selecting c.Name and hence your a is no longer of type data_qy, it becomes a string.

Try this:

var query = (from c in db.data_qy
           where c.UploadDate == yesterday && c.Cover == "prest"
           select (c)).OrderByDescending(a => a.UploadDate).Distinct();

i.e. instead of selecting c.Name, select c, it should work.

EDIT:

Also, I see that you need only distinct Names, so you can get them as:

var query = (from c in db.data_qy
           where c.UploadDate == yesterday && c.Cover == "prest"
           select (c)).OrderByDescending(a => a.UploadDate)
           .Select(a => a.Name).Distinct();

Hence your 'UploadDate' property is null-able, you have to use c.UploadDate.Value.

var query = (from c in db.data_qy
                          where c.UploadDate.Value == yesterday &&
                                c.Cover == "prest"
                          select (c)).OrderByDescending(a => a.UploadDate.Value).Distinct();

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