Question

Having a hard time wrapping my head around this one. I have a Page entity and a Keyword entity. I’ve created a member variable called $keywords in my Page entity that has a ManyToMany association that creates a join table called “pages_keywords”. In my application, I want to give the ability to add a keyword to a page. How would I go about adding that record to the database?

I can access the Page entity’s $keywords member variable but I’m not sure where to go from there. I see that the Doctrine implementation of ArrayCollection has an add() method that just takes a value. Can I just pass it the Keyword entity’s id and will that create the record for me?

Answer 1

Assuming you know the primary key value of the entity you are looking to associate it with (in your example, the $keywordId), the best way to do this is to get a reference to the entity. This gets you a reference without doing a database lookup for the associated entity.

The solution you posted in your follow-up answer has the disadvantage of requiring an extra trip to the database to retrieve the keyword record. Retrieving it as a reference means that there is no extra database lookup:

<?php

// assumes $this->em is already defined as the Doctrine2 EntityManager
$page = $this->em->getRepository('App\Entity\Page')->find($pageId);

// associate $keyword with $page via a reference to the keywordId
$keyword = $this->em->getReference('App\Entity\Keyword', $keywordId);
$page->getKeywords()->add($keyword);
$em->flush();