首页 \ 问答 \ 如何将`var`变量等同于另一个查询(How to equate `var` variable to another query)

如何将`var`变量等同于另一个查询(How to equate `var` variable to another query)

我有一个名为retVal的var变量,它等于某个查询。 在某些条件之后,我想将它等同于另一个查询。 但我得到一个错误,如implicit cast of type "System.Collections.Generic.IEnumerable<AnonymousType#1>" in "System.Collections.Generic.IEnumerable<AnonymousType#2>" is impossible 。 你可以问我为什么我不想定义另一个var变量。 因为这个用于foreach循环。 我们来看看代码:

var retVal = from groupItem in result.AsEnumerable()
                             where groupItem.Sms.First().amountOfParts == (
                               (from item in rawSmsList.AsEnumerable()
                                where item.referenceNumber == groupItem.Sms.First().referenceNumber
                                select item).Count()
                             )
                             select new
                             {
                                 Value = groupItem.Value,
                                 Sms = groupItem.Sms
                             };
                //CONDITION
                if (retVal.ToArray().Length==0)
                {
                    //HERE I NEED TO RETVAL EQUATE NEW QUERY
                    retVal = from groupItem in result.AsEnumerable()
                                 where groupItem.Sms.First().amountOfParts == (
                                   (from item in rawSmsList.AsEnumerable()
                                    where item.senderNumber == groupItem.Sms.First().senderNumber
                                    select item).Count()
                                 )
                                 select new
                                 {
                                     Value = groupItem.Value,
                                     Sms = groupItem.Sms
                                 };                        
                }

                foreach (var item in retVal)//FOREACH EXPECTS THE SAME RETVAL!!!

那么如何将不同的查询转换为相同的var变量? 或者如何找到var变量的类型然后将其转换为新定义的变量?


I have varvariable called retVal which equals to some query. After some conditions I want to equate it to another query. But I get an error like implicit cast of type "System.Collections.Generic.IEnumerable<AnonymousType#1>" in "System.Collections.Generic.IEnumerable<AnonymousType#2>" is impossible. You can ask me why I don't want to define another var variable. Because this one is used in foreach cycle. Let's have a look on the code:

var retVal = from groupItem in result.AsEnumerable()
                             where groupItem.Sms.First().amountOfParts == (
                               (from item in rawSmsList.AsEnumerable()
                                where item.referenceNumber == groupItem.Sms.First().referenceNumber
                                select item).Count()
                             )
                             select new
                             {
                                 Value = groupItem.Value,
                                 Sms = groupItem.Sms
                             };
                //CONDITION
                if (retVal.ToArray().Length==0)
                {
                    //HERE I NEED TO RETVAL EQUATE NEW QUERY
                    retVal = from groupItem in result.AsEnumerable()
                                 where groupItem.Sms.First().amountOfParts == (
                                   (from item in rawSmsList.AsEnumerable()
                                    where item.senderNumber == groupItem.Sms.First().senderNumber
                                    select item).Count()
                                 )
                                 select new
                                 {
                                     Value = groupItem.Value,
                                     Sms = groupItem.Sms
                                 };                        
                }

                foreach (var item in retVal)//FOREACH EXPECTS THE SAME RETVAL!!!

So how to cast different queries to the same var variable? Or how to find type of var variable and then cast it to a new defined variable?


原文:https://stackoverflow.com/questions/15651955
更新时间:2019-12-13 07:41

最满意答案

var表示隐式类型变量,这意味着它的类型将在编译时确定,所以在你的第一次使用时它会被分配一个匿名类型,在你的第二个你试图给它分配一个不同的匿名类型,你不能这样做。

您可以修改代码以使用类而不是匿名对象,然后投射到该代码,然后您将执行您现在正在执行的操作。 您可以创建类,如:

public class MyClass 
{
   public int Value {get;set;}
   public string Sms {get;set;}
}

然后通过将select语句修改为:

var retVal = ......
             select new MyClass
               {
                  Value = groupItem.Value,
                   Sms = groupItem.Sms
               };  

var means implicitly typed variable, that means its type will be determined at compile time, So on your first usage it will be assigned an anonymous type, in your second you are trying to assign it a different anonymous type, you can't do that.

You can modify your code to use a class instead of anonymous object and then project to that, then you will be to do what you are doing now. You can create the class like:

public class MyClass 
{
   public int Value {get;set;}
   public string Sms {get;set;}
}

and then project it by modifying your select statement as:

var retVal = ......
             select new MyClass
               {
                  Value = groupItem.Value,
                   Sms = groupItem.Sms
               };  
2013-03-27

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