与WCF一起使用时如何在linq中给别名 [英] How To give alias in linq when use with WCF

问题描述

我在WCF上使用LINQ
在.dbml文件中，我拖动了sql表，在IService1.cs文件中，我的代码是:

I am using LINQ with WCF
in the .dbml file I dragged the sql table, my code in IService1.cs file is:

[OperationContract]
List<ASX_D> ASX_D12(String tablename, String company);

我在Service1.svc.cs中的代码是

and my code in Service1.svc.cs is

public List<ASX_D> ASX_D12(string tablename, string company)
{
    var q = (from p in db.ASX_Ds
            where p.ASX_D_name == company
            select new      
    {
      qq=p.ASX_D_close ,
      ff=p.ASX_D_date,
      ss=p.ASX_D_exchange,
      oo=p.ASX_D_high,
      gg=p.ASX_D_low,
      fg=p.ASX_D_name,
      dfgdfg=p.ASX_D_open
      qweqwe=p.ASX_D_sector,
      cvbcvb=p.ASX_D_symbol,
      aedasew=p.ASX_D_time,
      sdfsdf=p.ASX_D_type,ruwoeru=p.ASX_D_volume
   });
   return q.ToList();

但它给出了错误

but it give the error

Cannot implicitly convert type 'System.Collections.Generic.List<AnonymousType#2>' to 'System.Collections.Generic.List<SilverlightProjectwithWCF.Web.ASX_D>' C:\Documents and Settings\hgtech\Desktop\SilverlightProjectwithWCF\SilverlightProjectwithWCF.Web\Service1.svc.cs    134 20  SilverlightProjectwithWCF.Web

How we can give an alias to columns in a LINQ query?

推荐答案

此代码应该有效:

This code should work:

var q = (from p in db.ASX_Ds
         where p.ASX_D_name == company
          select p;
return q.ToList();

不需要中间匿名类型，实际上不能将其强制转换为泛型中的返回类型，因此，您想要的类型别名对于像C#这样的强OO语言来说是不起眼的.

如果要限制字段，则应声明 DataContract [列表< T>.方法 [ ^ ]

即使您要发送所有数据，这种转换也是值得的，因为它将接口与对象模型和数据库实现分离开来，并允许服务的版本控制.

The intermediate anonymous type is not required, in fact it can''t be cast to the return type in the generic, so the type aliasing you want is a non-starter in a strongly OO language like C#.

If you want to restrict the fields you should declare a DataContract[^]with the fields you want and convert, you can write convertor method and an call
q.ToList().ConvertAll<datacontracttype>(ConversionFunction);

See List<T>.ConvertAll<TOutput> Method [^]

Such conversion is worthwhile even if you want to send all the data as it de-couples your interface from your object model and database implementation and allows versioning of the service.

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