Linq returning IEnumerable<T>

Question

I wish to return enumerable items in order to bind the nested grid. Top grid displays Book Title and the nested grid displays the authors list of that book.

Author Collection

static public Author[] Authors =
{
    new Author {FirstName="Johnny", LastName="Good"},
    new Author {FirstName="Graziella", LastName="Simplegame"},
    new Author {FirstName="Octavio", LastName="Prince"},
    new Author {FirstName="Jeremy", LastName="Legrand"}
}

Book Collection

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]
    }
};

1) How to write a Enumerable method that can return the following query ?

(ofcourse my implementation is wrong )

 public IEnumerable<Book> GetBook()
 {
    IEnumerable<Book> booklist
    =  from book in SampleData.Books
          select new Book
            {
             Title = book.Title,
             Authors = 
                      from author in SampleData.Authors
                      where book.Authors == author
                      select new Author
                      {
                         FirstName = author.FirstName
                       }
             };
    return booklist;
}

2) The output I received ( the nested BulletedList is not filled with author's first name).

Authors     Title
---------------------------
            Funny Stories
            LINQ rules
            C# on Rails
            All your base are  belong to us 
            Bonjour mon Amour

I suspect the problem is in

where book.Authors == author  (checking Types with == operator).

Html Code

<asp:GridView ID="GridView2" runat="server" AutoGenerateColumns="False">
     <Columns>
           <asp:TemplateField HeaderText="Author List">
               <ItemTemplate>
                       <asp:BulletedList ID="BulletedList1" runat="server" 
                         DataSource='<%# Eval("Authors") %>'>
                        </asp:BulletedList>
                </ItemTemplate>
            </asp:TemplateField>
          <asp:BoundField DataField="Title" HeaderText="Title"
           SortExpression="Title" />
      </Columns>
 </asp:GridView>

How to improve the coding to get the proper result?

Answer 1

Instead of using Eval("Authors"), use Eval("Authors.FirstName").

Also, you don't need the join between books and Authors. You can just select the .Authors property from the book object. (I take it that Authors is actually a typo and it should be "Author" in this case?)

Answer 2

Instead of:

where book.Authors == author

You should do something like:

where book.Authors.Contains(author)

Obviously == doesn't work because you compare one author to a collection of authors. You want to check if the collection of authors of the book contains the specified author instead.