Doctrine may modify other documents

At work, I am currently using MongoDB with Doctrine ODM.

The Problem

I have a document that are indirectly related to each other.

Let’s say I have a document called Posts and the Posts document has a function called getComments that returns a CommentCollection.

We also have a document called BackupComments. The BackupComments document is just a place to store a modified version of the comments. Let’s say we want to modify the format of the date from comments and store it in the BackupComments document.

  $posts = $this->dm->getRepository(Posts::class)->findOne();
  $comments = $posts->getComments();


  // This will be where your problem is. We want to do it in an easy way
  foreach ($comments as $comment) {
    $backupComment = new BackupComments();

    $modifiedComment = $comment->getComment();
    $date = $comment->getDate();
    $modifiedComment = $date->format('Y-m-d H:i:s') . ': ' . $modifiedComment;

    $comment->setComment($modifiedComment);

    $backupComment->setComment($modifiedComment);
    $this->dm->persist($backupComment);
  }

  $this->dm->flush();

The problem with this code is that the Comment document is being modified. This is because of how PHP references objects. When you modify the $comment object, you are also modifying the Comment document indirectly.

Solution

Thankfully, this is very easy to fix. You can use the clone keyword to create a new instance of the object or just modify the raw data.

We will use the latter method in this example.

  $posts = $this->dm->getRepository(Posts::class)->findOne();
  $comments = $posts->getComments();

  foreach ($comments as $comment) {
    $backupComment = new BackupComments();

    $modifiedComment = $comment->getComment();
    $date = $comment->getDate();
    $modifiedComment = $date->format('Y-m-d H:i:s') . ': ' . $modifiedComment;

    $comment->setComment($modifiedComment);

    // Just create a new instance of the Comment object
    $newComment = new Comment();
    $newComment->setComment($modifiedComment);

    // This will not modify the original Comment object
    $backupComment->setComment($modifiedComment);
    $this->dm->persist($backupComment);
  }

  $this->dm->flush();

Now, the Comment document will not be modified. The BackupComments document will have the modified comments.

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Table of contents

Doctrine may modify other documents

The Problem

Solution