是否可以在C＃中的LINQ扩展方法中创建匿名类型？

Question

Is it possible to create anonymous type in LINQ extension methods in C#?

For example LINQ query.ie

var CAquery = from temp in CAtemp
 join casect in CAdb.sectors
 on temp.sector_code equals casect.sector_code
 select new
 {       
     //anonymous types
     CUSIP = temp.equity_cusip,
     CompName = temp.company_name,
     Exchange = temp.primary_exchange       
 };

Is the same behavior supported for LINQ extension methods in C#?

Answer 1

Do you mean "when using the extension method syntax"? If so, absolutely. Your query is exactly equivalent to:

var CAquery = CAtemp.Join(CAdb.sectors,
                          temp => temp.sector_code,
                          casect => casect.sector_code,
                          (temp, casect) => new
                          {       
                              CUSIP = temp.equity_cusip,
                              CompName = temp.company_name,
                              Exchange = temp.primary_exchange       
                          });

The C# language specification sets out all the translations in section 7.16. Note that in this case, as your join clause was only followed by a select clause, the projection is performed within the Join call. Otherwise (eg if you had a where clause) the compiler would have introduced transparent identifiers to keep the two range variables ( temp and casect ) available, via a new anonymous type which just kept the pair of them in a single value.

Every query expression is expressible as non-query-expression code. Query expressions are effectively a form of preprocessing.

Answer 2

something like this maybe...

var CAquery=CATemp.Join(.....)
                  .Select(temp=>new
                           {       
                           CUSIP = temp.equity_cusip,
                           CompName = temp.company_name,
                           Exchange = temp.primary_exchange       
                           });

Answer 3

The LINQ query you have shown is an extension method. It will simply be transformed by the compiler into a call to the Join extension method. You can create an anonymous type anywhere you can create any type, which include inside any extension methods.