Update a many-to-many relationship in Doctrine

Question

I have an article-category relationship and I'd like to update the relationship when necessary. That means, adding or removing the desired categories from an article. I use a php (ZF) setup with Doctrine 1.2. In YAML, the config looks (simplified) like this:

Article:
  columns:
    id: bigint(10)

Category:
  columns:
    id: bigint (10)
  relations:
    articles:
      foreignAlias: categories
      class: Article
      refClass: CategoryArticle

CategoryArticle:
  columns:
    category_id: bigint (10)
    article_id: bigint (10)
  relations:
    category:
      class: Category
      foreignAlias: categoryArticle
    article:
      class: Article
      foreignAlias: categoryArticle

I have a persisted $article where all old categories are available. With a POST request I get a list of category ids which should be the new ones. I have this so far:

$oldCategories = array();
foreach ($article->categories as $cat) {
    $oldCategories[] = $cat->id;
}
$newCategories = $form->getValue('categories');

$diffRemove = array_diff($oldCategories, $newCategories);
$diffAdd    = array_diff($newCategories, $oldCategories);
foreach ($diffRemove as $id) {
    // Remove all the categories $id from article [1]
}
foreach ($diffAdd as $id) {
    // Add all the categories $id to article [2]
}

My question is about [1] and [2]. What is the best performance to add and remove a many:many relationship?

Answer 1

Deletion

The most efficient way of deleting en masse in SQL is using single sql statement with some conditions set, something like

delete from Products where id>3

It make use of indexes, partitioning, etc.

There is a way to achieve that value of performance using Doctrine 1.2 - using DQL DELETE statements. As shown in documentation, the following query transforms into the above SQL:

$q = Doctrine_Query::create()
    ->delete('Products p')
    ->where('p.id > 3');

In your case, you could optimize deletion with something like

$q = Doctrine_Query::create()
    ->delete('CategoryArticle ca')
    ->where('ca.article_id=?', $article_id)
    ->andWhereIn('ca.category_id', $diffRemove);

This code should generate something like:

delete from CategoryArticle 
where article_id = $article_id and category_id in ($diffremove)

Insertion

With insertion you could use CategoryArticle entity. The most effective way to do that with Doctrine is to build up a collection of Entities and than save that collecion:

$collection = new Doctrine_Collection('CategoryArticle');
foreach ($diffAdd as $id){
    $ca = new CategoryArticle();
    $ca->category = $id;
    $ca->article = $article_id;
    $collection[] = $ca;
}

$collection->save();