LINQ左联接的问题

Question

        我从查询表达式转成查询操作符的写法，但是结果总是不对        //查询表达式        GridViewLeftOuterJoin.DataSource =          from publisher in SampleData.Publishers          join book in SampleData.Books on publisher equals book.Publisher into publisherBooks          from book in publisherBooks.DefaultIfEmpty ()          select new {              Publisher = publisher.Name ,              Book = book == default ( Book ) ? "(no books)" : book.Title          };        GridViewLeftOuterJoin.DataBind ();         正确结果：            //Publisher      Book             //FunBooks       Funny Stories             //FunBooks       Bonjour mon Amour             //Joe Publishing LINQ rules             //Joe Publishing C# on Rails             //Joe Publishing All your base are belong to us             //I Publisher    (no books)                 //查询操作符        GridViewLeftOuterJoin1.DataSource = SampleData.Publishers                                            .Join ( SampleData.Books ,                                                        p => p ,                                                        b => b.Publisher ,                                                        ( b , pb ) => new {                                                            Publisher = b.Name ,                                                            Book = pb == default ( Book ) ? "(no books)" : pb.Title                                                        } ).DefaultIfEmpty ();         GridViewLeftOuterJoin1.DataBind ();         结果（错误）：            //Publisher      Book             //FunBooks       Funny Stories             //FunBooks       Bonjour mon Amour             //Joe Publishing LINQ rules             //Joe Publishing C# on Rails             //Joe Publishing All your base are belong to us 以下为数据源： static public class SampleData  {    static public Publisher[] Publishers =    {      new Publisher {Name="FunBooks"},      new Publisher {Name="Joe Publishing"},      new Publisher {Name="I Publisher"}    };    static public Book[] Books =    {      new Book {        Title="Funny Stories",        Publisher=Publishers[0],        Authors=new[]{Authors[0], Authors[1]},        PageCount=101,        Price=25.55M,        PublicationDate=new DateTime(2004, 11, 10),        Isbn="0-000-77777-2",        Subject=Subjects[0]      },      new Book {        Title="LINQ rules",        Publisher=Publishers[1],        Authors=new[]{Authors[2]},        PageCount=300,        Price=12M,        PublicationDate=new DateTime(2007, 9, 2),        Isbn="0-111-77777-2",        Subject=Subjects[0]      },      new Book {        Title="C# on Rails",        Publisher=Publishers[1],        Authors=new[]{Authors[2]},        PageCount=256,        Price=35.5M,        PublicationDate=new DateTime(2007, 4, 1),        Isbn="0-222-77777-2",        Subject=Subjects[0]      },      new Book {        Title="All your base are belong to us",        Publisher=Publishers[1],        Authors=new[]{Authors[3]},        PageCount=1205,        Price=35.5M,        PublicationDate=new DateTime(2006, 5, 5),        Isbn="0-333-77777-2",        Subject=Subjects[2]      },      new Book {        Title="Bonjour mon Amour",        Publisher=Publishers[0],        Authors=new[]{Authors[1], Authors[0]},        PageCount=50,        Price=29M,        PublicationDate=new DateTime(1973, 2, 18),        Isbn="2-444-77777-2",        Subject=Subjects[1]      }    };  }

Answer 1

 

 GridViewLeftOuterJoin1.DataSource =
SampleData.Publishers
         .GroupJoin ( SampleData.Books , p => p , b => b.Publisher ,
                         ( b , pb ) => new { b , pb } )
         .SelectMany ( pb => pb.pb.DefaultIfEmpty () ,
                         ( b , pb ) => new {
                          Publisher = b.b.Name ,
                          Book = pb == default ( Book )
                                      ? "(no books)" : pb.Title
          } );

        GridViewLeftOuterJoin1.DataBind ();