README

The library is a single class that allows you to load many related entities in an optimal way and performance.

Doctrine UnitOfWork's identityMap used for loading. So method "clear" in UnitOfWork breaks loading.

Usage

Use blog structure with users, posts, comments and likes for example.

/** @ORM\Entity() */
class User
{
    /**
     * @ORM\Id()
     * @ORM\Column(type="integer")
     */
    public $id;

    /** @ORM\Column(type="string") */
    public $name;
    
    /** @ORM\Column(type="string") */
    public $country;

    /** @ORM\OneToMany(targetEntity="Post", mappedBy="user") */
    public $posts;
}

/** @ORM\Entity() */
class Post
{
    /**
     * @ORM\Id()
     * @ORM\Column(type="integer")
     */
    public $id;

    /** @ORM\Column(type="string") */
    public $title;

    /** @ORM\Column(type="string") */
    public $content;

    /**
     * @ORM\ManyToOne(targetEntity="User")
     * @ORM\JoinColumn(name="user_id", referencedColumnName="id")
     */
    public $user;

    /** @ORM\OneToMany(targetEntity="Comment", mappedBy="post") */
    public $comments;

    /** @ORM\OneToMany(targetEntity="Like", mappedBy="post") */
    public $likes;
}

/** @ORM\Entity() */
class Comment
{
    /**
     * @ORM\Id()
     * @ORM\Column(type="integer")
     */
    public $id;

    /** @ORM\Column(type="string") */
    public $content;

    /**
     * @ORM\ManyToOne(targetEntity="Post")
     * @ORM\JoinColumn(name="post_id", referencedColumnName="id")
     */
    public $post;

    /**
     * @ORM\ManyToOne(targetEntity="User")
     * @ORM\JoinColumn(name="user_id", referencedColumnName="id")
     */
    public $user;
}

/**
 * @ORM\Entity()
 * @ORM\Table(name="`like`")
 */
class Like
{
    /**
     * @ORM\Id()
     * @ORM\Column(type="integer")
     */
    public $id;

    /**
     * @ORM\ManyToOne(targetEntity="Post")
     * @ORM\JoinColumn(name="post_id", referencedColumnName="id")
     */
    public $post;

    /**
     * @ORM\ManyToOne(targetEntity="User")
     * @ORM\JoinColumn(name="user_id", referencedColumnName="id")
     */
    public $user;
}

Now we count the number of countries from which we put Like for a specific user (just for example, it is better to use the calculation in the database).

$countries = [];
$user = $this->em->getRepository(User::class)->find(1);
foreach ($user->posts as $post) {
    foreach ($post->likes as $like) {
        $countries[$like->user->country] = 1;
    }
}
$num = count($countries);

By default, you will perform the number of queries to the database = number of posts + number of users + 2:

SELECT * FROM user WHERE id = 1;
SELECT * FROM post WHERE user_id = 1;
SELECT * FROM `like` WHERE post_id = ?; # for each post
SELECT * FROM user WHERE id = ?; # for unique user

Queries quantity is too large. I want to merge identical queries to the same table:

SELECT * FROM `like` WHERE post_id IN (?); # for all post
SELECT * FROM user WHERE id IN (?); # for all unique users

You can use eager loading, but it does not work with a large cascade of entities. Another way to use RelationsLoader from this library.

$countries = [];
$user = $this->em->getRepository(User::class)->find(1);

$relationsLoader = new RelationsLoader($this->em);
$relationsLoader->load($user, ['posts' => ['likes' => ['user']]]);

foreach ($user->posts as $post) {
    foreach ($post->likes as $like) {
        $countries[$like->user->country] = 1;
    }
}
$num = count($countries);

In this case, 4 queries to the database will be executed.

Syntax

In RelationsLoader::load, you must pass the data for which you want to load the relations (entity, array of entities, collection) and a hierarchical list of relationships to load. How is formed a hierarchical list of consider examples.

• Loading posts for the users (similar to eager loading in doctrine):

    $relationsLoader->load($users, ['posts']);
  

• Loading posts and likes for posts:

    $relationsLoader->load($users, [
        'posts' => ['likes']
    ]);
  

• Loading posts, comments and likes for posts:

    $relationsLoader->load($users, [
        'posts' => [
            'comments',
            'likes'
        ]
    ]);
  

• Loading posts, comments and likes for posts, users for comments:

    $relationsLoader->load($users, [
        'posts' => [
            'comments' => ['user'],
            'likes'
        ]
    ]);
  

• Loading posts, comments and likes for posts, users for comments and likes:

    $relationsLoader->load($users, [
        'posts' => [
            'comments' => ['user'],
            'likes' => ['user']
        ]
    ]);