title: EF Core many-to-many linq query
body: <p>If I have the following classes mapping a many-to-many relationship in EF Core:</p>
  <pre><code>public class Book
  {
      public int BookId { get; set; }
      public string Title { get; set; }
      public Author Author { get; set; }
      public ICollection&lt;BookCategory&gt; BookCategories { get; set; }
  }  
  public class Category
  {
      public int CategoryId { get; set; }
      public string CategoryName { get; set; }
      public ICollection&lt;BookCategory&gt; BookCategories { get; set; }
  }  
  public class BookCategory
  {
      public int BookId { get; set; }
      public Book Book { get; set; }
      public int CategoryId { get; set; }
      public Category Category { get; set; }
  }
  </code></pre>
  <p>what is be the best practice to get a <code>List&lt;Category&gt;</code> from the Book instance?
  In EF6 I was able to just Query <code>Book.Categories</code></p>