Strange behaviour with LINQ-to-Entities Include

Question

I've realised that I don't fully understand the Include method in LINQ-to-Entities.

For example, take the two code snippets below. I would expect them to produce the same output (though the first version may be more efficient because it avoids JOINs).

// Snippet 1
using (var db = new Db()) {
  var author = db.Authors.First();
  db.LoadProperty<Author>(author, o => o.Books);
  foreach (var book in author.Books) {
    db.LoadProperty<Book>(book, o => o.Editions);
    foreach (var edition in book.Editions)
      Response.Write(edition.Id + " - " + edition.Title + "<br />");
  }
}

Response.Write("<br />");

// Snippet 2
using (var db = new Db()) {
  var author = db.Authors.Include("Books.Editions").First();
  foreach (var book in author.Books) {
    foreach (var edition in book.Editions)
      Response.Write(edition.Id + " - " + edition.Title + "<br />");
  }
}

But the output for each snippet is different:

1 - Some Book First Edition
2 - Another Book First Edition
3 - Another Book Second Edition
4 - Another Book Third Edition

8 - Some Book First Edition
9 - Another Book First Edition

The first snippet correctly outputs {Edition Id} - {Edition Title}, whereas the second one unexpectedly prints {Book Id} - {Edition Title} and only gives the first edition of each book.

What's going on? And is there a way to achieve the desired output using Include?

EDIT 1: The MySql data looks like (corrected):

Authors         = { { Id = 1, Name = "Some Author" } }

Books           = { { Id = 8, AuthorId = 1 },
                    { Id = 9, AuthorId = 1 } }

Editions        = { { Id = 1, Title = "Some Book First Edition" },
                    { Id = 2, Title = "Another Book First Edition" },
                    { Id = 3, Title = "Another Book Second Edition" },
                    { Id = 4, Title = "Another Book Third Edition" } }

EditionsInBooks = { { BookId = 8, EditionId = 1 },
                    { BookId = 9, EditionId = 2 },
                    { BookId = 9, EditionId = 3 },
                    { BookId = 9, EditionId = 4 } }

Note that there is no Edition with Id = 8 or Id = 9.

And the code above is my complete code, in Page_Load for an empty test page.

EDIT 2: I've tested the following and they don't make a difference:

1. var author = db.Authors.Include("Books.Editions").AsEnumerable().First();
2. var author = db.Authors.Include("Books.Editions").Single(o => o.Id == 1);
3. var author = db.Authors.Include("Books").Include("Books.Editions").First();

EDIT 3: If I enable Lazy Loading, the following works (in Snippet 2):

var author = db.Authors.First();

(This is essentially doing the same as Snippet 1, I suppose.)

However, this still returns the strange output irrespective of Lazy Loading:

var author = db.Authors.Include("Books.Editions").First();

EDIT 4: I'm really sorry, but I misrepresented the table structure above. (I'm having one of those days.) It's now corrected, to show the many-to-many relationship. Please see Edit 1.

Also the output for

((ObjectQuery)db.Authors.Include("Books.Editions").AsEnumerable())
  .ToTraceString()

is

SELECT
  `Project1`.`Id`,
  `Project1`.`Name`,
  `Project1`.`C2` AS `C1`,
  `Project1`.`id1`,
  `Project1`.`AuthorId`,
  `Project1`.`C1` AS `C2`,
  `Project1`.`id2`,
  `Project1`.`Title`
FROM (SELECT
  `Extent1`.`Id`,
  `Extent1`.`Name`,
  `Join2`.`Id` AS `id1`,
  `Join2`.`AuthorId`,
  `Join2`.`Id` AS `id2`,
  `Join2`.`Title`,
   CASE WHEN (`Join2`.`Id` IS NULL) THEN (NULL)
        WHEN (`Join2`.`BookId` IS NULL) THEN (NULL)
        ELSE (1) END AS `C1`,
   CASE WHEN (`Join2`.`Id` IS NULL) THEN (NULL)
        ELSE (1) END AS `C2`
   FROM `authors` AS `Extent1`
     LEFT OUTER JOIN (SELECT
       `Extent2`.`Id`,
       `Extent2`.`AuthorId`,
       `Join1`.`BookId`,
       `Join1`.`EditionId`,
       `Join1`.`Id` AS `Id1`,
       `Join1`.`Title`
       FROM `books` AS `Extent2`
       LEFT OUTER JOIN (SELECT
         `Extent3`.`BookId`,
         `Extent3`.`EditionId`,
         `Extent4`.`Id`,
         `Extent4`.`Title`
         FROM `editionsinbooks` AS `Extent3`
         INNER JOIN `editions` AS `Extent4`
           ON `Extent4`.`Id` = `Extent3`.`EditionId`) AS `Join1`
       ON `Extent2`.`Id` = `Join1`.`BookId`) AS `Join2`
     ON `Extent1`.`Id` = `Join2`.`AuthorId`) AS `Project1`
   ORDER BY
     `Project1`.`Id` ASC,
     `Project1`.`C2` ASC,
     `Project1`.`id1` ASC,
     `Project1`.`C1` ASC

The CASE statements are interesting, given that none of my MySql fields are nullable.

Answer 1

There might be a bug in Entity Framework's provider's compiling of the First() expression in the LINQ statement. There's occasional weirdness when Include is involved: http://wildermuth.com/2008/12/28/Caution_when_Eager_Loading_in_the_Entity_Framework

Try rewriting the second snippet to be:

using (var db = new Db()) {
    var author = db.Authors.Include("Books.Editions").AsEnumerable().First();
    foreach (var book in author.Books)
    {
        foreach (var edition in book.Editions)
        {
            Response.Write(edition.Id + " - " + edition.Title + "<br />");
        }
    }
}

If that fixes your output, then it's definitely the First() method.

EDIT: You are correct about your third edit doing the same thing as snippet 1. I can't fathom how that include statement is tripping things up so badly. The only thing I could encourage is to look at the SQL query it's generating:

var sql = ((System.Data.Objects.ObjectQuery)db.Authors.Include("Books.Editions").AsEnumerable().First()).ToTraceString();

EDIT 2: It may very well be possible that the problem is in your MySQL provider for EF, given the crazy sql output generated.