LINQ Tutorials

@inherits Custom.Hybrid.Razor14
@using System.Linq;
@using Dynlist = System.Collections.Generic.IEnumerable<dynamic>;

<!-- unimportant stuff, hidden -->

@{
  var persons = AsList(App.Data["Persons"]);
  var books = AsList(App.Data["Books"]);
}

@Html.Partial("_header.cshtml")

<div class="row">
  <div class="col-lg-7">
    <h2>Grouping by Authors, a List inside of Books</h2>
  </div>
  @Html.Partial("../shared/_DefaultInfoSection.cshtml")

</div>

<h3>GroupBy Authors - bad example</h3>
<p>This example will group the books by the <code>Authors</code> property. This example doesn't give us what we want, because authors that exist in sets and alone are grouped separately. </p>

<ol>
  @foreach(var group in books.GroupBy(b => b.Authors)) {
    <li>
      Group
      <ul>
        @foreach(var book in group) {
          <li>
            <strong>@book.Title</strong> by
            @string.Join(",",(book.Authors as Dynlist).Select(a => a.FirstName + " " + a.LastName))
          </li>
        }
      </ul>
    </li>
  }
</ol>




<hr>
<h3>GroupBy Authors - better example</h3>
<p>Let's do it better, and group by each Author individually</p>

<ol>
  @{ 
    var booksGroupedByAuthor = books
      .SelectMany(b => (b.Authors as Dynlist).Select(a => new { Book = b, Author = a }))
      .GroupBy(set => set.Author);
    
    foreach(var group in booksGroupedByAuthor) {
    <li>
      Author: @group.Key.FirstName @group.Key.LastName
      <ul>
        @foreach(var set in group) {
          <li>
            <strong>@set.Book.Title</strong> by
            @string.Join(",",(set.Book.Authors as Dynlist).Select(a => a.FirstName + " " + a.LastName))
          </li>
        }
      </ul>
    </li>
  }
  }
</ol>



<hr>
<h3>GroupBy Authors - Example starting with Authors</h3>
<p>In this example, we'll start with the authors list. This is probably not ideal - as some people are not authors, but it's a good learning example. To find the books we have to navigate through <code>Parents(...)</code> because in our data-model, the books reference authors, not the authors to books.</p>

<ol>
  @foreach(var author in persons) {
    // this line would work, if Books only had people in the Authors. 
    // but it doesn't, there are also illustrators, which is why we use the second example instead
    var peoplesBooks = author.Parents("Books");
    var authorsBooks = author.Parents("Books", "Authors");

    <li>
      @author.FirstName @author.LastName
      <ul>
        @foreach(var book in authorsBooks) {
          var coAuthors = (book.Authors as Dynlist).Where(a => a != author);
          <li>
            <strong>@book.Title</strong> 
            @if(coAuthors.Any()) {
              <span>co-authored by 
                @string.Join(",", coAuthors.Select(a => a.FirstName + " " + a.LastName))
              </span>
            }
          </li>
        }
      </ul>
    </li>
  }
</ol>



<!-- unimportant stuff, hidden -->