1. Relation
2. Example of 1:N relation : Author and Post
3. Task 1 : Search by Main Attribute, without Relation
4. Task 2 : Search by Main Attribute, with Relation
5. Task 3 : Search by HAS_ONE Attribute, with Relation
6. Task 4 : Search by HAS_MANY Attribute, without Relation
7. Task 5 : Search by HAS_MANY Attribute, with Relation
8. Task 6 : Search by HAS_MANY Attribute, with Relevant Relations
9. Task 7 : LIMIT and ORDER
10. Task 8: LIMIT and ORDER, with Relevant Relations
11. Summary

This article tries to describe the practical techniques of searching by a HAS_MANY relation using ActiveRecord of Yii 2.0.

In Yii 1.1, we sometimes got lost trying to search by a HAS_MANY relation. The wiki article Drills : Search by a HAS_MANY relation in Yii 1.1 was an effort to offer some practical techniques of searching by a HAS_MANY relation in Yii 1.1.

Now, we have Yii 2. Let's examine what we can do with the new ActiveRecord of Yii 2 when we have to solve the same tasks of searching by a HAS_MANY relation.

Relation ¶

Two entities are sometimes connected with a relation of 1:N. Or we may say that 1:N is the only possible relation between 2 entities as long as we are in the RDB world. 1:1 relation is just a particular kind of 1:N where N is always assumed to be 1 at the maximum. And N:N relation can be considered as a combination of two 1:N relations (N:1-1:N).

Yii supports this 1:N relation in ActiveRecord as HAS_ONE and HAS_MANY relations. 1:N relation seen from the side of N is HAS_ONE, and from the side of 1 it is HAS_MANY.

Now, let's construct an example of 1:N relation.

Example of 1:N relation : Author and Post ¶

Think about blog posts and their authors. It's a relation of "An Author has many Posts" and "A Post has an Author" at the same time. This pair of relations is represented with the following code:

An Author has many Posts

/**
 * Author model
 * @property integer $id
 * @property string $name the author's name
 */
class Author extends \yii\db\ActiveRecord
{
    /**
     * @return \yii\db\ActiveQuery
     */
    public function getPosts()
    {
        return $this->hasMany(Post::className(), ['author_id' => 'id']);
    }

A post has one Author

/**
 * Post model
 * @property integer $id
 * @property integer $author_id FK to the author's id
 * @property string $title the title of the post
 */
class Post extends \yii\db\ActiveRecord
{
    /**
     * @return \yii\db\ActiveQuery
     */
    public function getAuthor()
    {
        return $this->hasOne(Author::className(), ['id' => 'author_id']);
    }

Note that a relation in Yii 2 is a getter method returning ActiveQuery.

We are going to solve the possible use cases of searching with this example.

Task 1 : Search by Main Attribute, without Relation ¶

Show all posts with a keyword

I want to start with a basic task. Let's retrieve all the posts that has a certain keyword in their titles.

// get all the posts that has a keyword in their title
$posts = Post::find()
    ->where(['like', 'title', $searchword])
    ->all();
// show the results
foreach($posts as $post) {
    echo "Title = {$post->title}\n";
}

Ah, it was too easy. And no relation is involved in this task.

OK, let's move on to the next.

Task 2 : Search by Main Attribute, with Relation ¶

Show all posts with a keyword, with their authors

Now we have to retrieve the authors' names, too.

Lazy Loading ¶

But this is quite easy if you don't care the efficiency. Just adding a line to echo $post->author->name would be enough.

// get all the posts that has a keyword in their title
$posts = Post::find()
    ->where(['like', 'title', $searchword])
    ->all();
// show the results
foreach($posts as $post) {
    echo "Title = {$post->title}\n";
    echo "Author = {$post->author->name}\n";
}

Post model has the author relation, so all you have to do to retrieve its Author is just accessing $post->author. How convenient is it! It's so-called lazy loading approach.

But the lazy loading approach has a drawback in this case, because you have to execute one query for retrieving an array of Posts, and every one query per each Post for retrieving its author. It will end up in 1+N queries to be executed.

SELECT * FROM `post` WHERE `title` LIKE `%searchword%`;
SELECT * FROM `author` WHERE `id`=1;
SELECT * FROM `author` WHERE `id`=2;
SELECT * FROM `author` WHERE `id`=5;
SELECT * FROM `author` WHERE `id`=7;
...

Eager Loading ¶

The better approach here is the following:

// get all the posts that has a keyword in their title, with their authors
$posts = Post::find()
    ->where(['like', 'title', $searchword])
    ->with('author')
    ->all();
// show the results
foreach($posts as $post) {
    echo "Title = {$post->title}\n";
    echo "Author = {$post->author->name}\n";
}

Here we are retrieveing Posts and their Authors at the same time by using yii\db\ActiveQuery::with(). It enables you to do the job with only 2 queries.

SELECT * FROM `post` WHERE `title` LIKE `%searchword%`;
SELECT * FROM `author` WHERE `id` IN (1,2,5,7,...);

Just after the 1st query retrieved the main models, the 2nd one will get all of the related models at once. In the above, (1,2,5,7,...) refers to the author_ids in the result set of the 1st query. This is so-called eager loading approach.

The eager loading is preferrable in this particular case, because it's more effective. But, you have to note, it is not always so.

Task 3 : Search by HAS_ONE Attribute, with Relation ¶

Show all posts with their authors who have a certain word in name

You have to search by an attribute in the related model, not in the main model.

// get all the posts that has a keyword in their author's name, with their authors
$posts = Post::find()
    ->joinWith('author')
    ->where(['like', 'author.name', $searchword])
    ->all();
// show the results
foreach($posts as $post) {
    echo "Title = {$post->title}\n";
    echo "Author = {$post->author->name}\n";
}

We join the author table using yii\db\ActiveQuery::joinWith(), because we have to search the main model by an attribute of the related model. Note that we may need to disambiguate the column name with the table name for the parameter of where.

The more important thing to note is that the joining tables using joinWith will not reduce the number of queries in the eager loading. You might think that just one query would be enough, but Yii will still use 2 queries, one for the main model and the other for the related model.

SELECT * FROM `post` 
    LEFT JOIN `author` ON `post`.`author_id` = `author`.`id`
    WHERE `author.name` LIKE `%searchword%`;
SELECT * FROM `author` WHERE `id` IN (1,2,5,7,...);

Yii 2 will always use the separated queries for the main model and the related models.

So, you would not be able to make the code more efficient by modifying with to joinWith in the answer for the task 2.

We join the related table using joinWith not because we expect good performance, but because we have to access a column in the related table in order to filter the rows in the main table.

And joinWith will cause ActiveRecord to choose the eager loading approach by default, but you may suppress the loading of the related models by specifying the optional parameter $eagerLoading as false.

You may say "It's just a HAS_ONE relation. Yeah, it's simple. I know."

Yes, you are right, definitely. Let's move on to the next task where we will deal with HAS_MANY.

Task 4 : Search by HAS_MANY Attribute, without Relation ¶

Show all authors who have a post with a keyword in its title

Now we will retrieve the authors, not the posts.

// get all the authors who have a post that has a keyword in its title
$authors = Author::find()
    ->joinWith('posts', false)  // will not get the related models
    ->where(['like', 'post.title', $searchword])
    ->all();
// show the results
foreach($authors as $author) {
    echo "Author = {$author->name}\n";
}

We join the posts relation using joinWith because we need post.title in the searching, while we set $eagerLoading to false because we don't need the posts to be retrieved.

Task 5 : Search by HAS_MANY Attribute, with Relation ¶

Show all authors who have a post with a keyword in its title, with all of their posts

// get all the authors who have a post that has a keyword in its title, with all of their posts
$authors = Author::find()
    ->joinWith('posts')  // will eagerly load the related models
    ->where(['like', 'post.title', $searchword])
    ->all();
// show the results
foreach($authors as $author) {
    echo "Author = {$author->name}\n";
    foreach($author->posts as $post) {
        echo "Title = {$post->title}\n";
    }
}

Don't forget that the query for the main model and those for the related models are separated. We add a condition using post.title in where part in order to filter the main models, but it doesn't affect the loading of the related models. The related models are loaded without any condition.

Well, then, what about the next task? It's a variation of the above.

Task 6 : Search by HAS_MANY Attribute, with Relevant Relations ¶

Show all authors who have a post with a keyword in its title, with all of their relevant posts

In fact, this is a little more confusing than the above.

Lazy Loading with Customized Relation ¶

One solution is this:

// get all the authors who have a post that has a keyword in its title
$authors = Author::find()
    ->joinWith('posts', false) // won't get posts
    ->where(['like', 'post.title', $searchword])
    ->all();
// show the results
foreach($authors as $author) {
    echo "Author = {$author->name}\n";
    // get all the posts that have a keyword in its title
    $posts = $author->getPosts()->where(['like', 'post.title', $searchword])->all();
    foreach($posts as $post) {
        echo "Title = {$post->title}\n";
    }
}

We join the posts relation using joinWith because we need post.title in the searching, while we set $leagerLoading to false because we don't want to load the posts at that point. And then we perform the lazy loading of the related posts with an on-the-fly condition for each author afterwards.

Eager Loading with Customized Relation ¶

You could specify an on-the-fly condition to the relation when you eagerly load the related models:

// get all the authors who have a post that has a keyword in its title
$authors = Author::find()
    ->joinWith('posts', false)  // this is for the main models
    ->where(['like', 'post.title', $searchword])
    ->with([    // this is for the related models
        'posts' => function($query) use ($searchword) {
            $query->where(['like', 'post.title', $searchword]);
        },
    ])
    ->all();
// show the results
foreach($authors as $author) {
    echo "Author = {$author->name}\n";
    foreach($posts as $post) {
        echo "Title = {$post->title}\n";
    }
}

Because we are applying the same condition to the relation for searching the main models and that for retrieving related models, we may use a single relation with that condition for both.

// get all the authors who have a post that has a keyword in its title
$authors = Author::find()
    ->innerJoinWith([
        'posts' => function($query) use ($searchword) {
            $query->where(['like', 'post.title', $searchword]);
        },
    ])
    ->all();
// show the results
foreach($authors as $author) {
    echo "Author = {$author->name}\n";
    foreach($posts as $post) {
        echo "Title = {$post->title}\n";
    }
}

In this way, you can use a customized relation for both the searching of the main models and the loading of the related models.

Let's move on to the next. It's a bit tough, though.

Task 7 : LIMIT and ORDER ¶

Show top 5 authors ordered by name who has a post with a key word in its title, with all of their posts

OK, so we need to add "LIMIT" and "ORDER". Going to try with this one.

Trial ¶

<?php
$authors = Author::find()
    ->joinWith('posts')
    ->where(['like', 'post.title', $searchword])
    ->orderBy(['author.name' => SORT_ASC])
    ->limit(5)
    ->all();
// show the results
foreach($authors as $author) {
    echo "Author = {$author->name}\n";
    foreach($author->posts as $post) {
        echo "Title = {$post->title}\n";
    }
}

You will notice that there is something strange in the output results. For example, the results may look like the following:

• search word = foo
• Author = Andy
  • Post = Don't use foo
  • Post = Use yoo for foo
  • Post = Don't use bar
  • Post = Use yar for bar
• Author = Ben
  • Post = foo is great
  • Post = I love foo
  • Post = I also love bar
• Author = Charlie
  • Post = What's foo?
  • Post = What's bar?
• end

We could get only 3 authors instead of 5.

Why did it happen? It was because the SQL used to retrieve the main models had been something like the following:

SELECT * from author
  LEFT JOIN post on author.id = post.author_id
  WHERE post.title LIKE '%foo%'
  ORDER BY author.name
  LIMIT 5

Notice that LIMIT 5 is applied to the number of the rows of an virtual table that is the result of joining author table with post table. The resulted rows may have less unique authors than the limit, because an author may have many posts.

In Yii 1.1, we could use GROUP BY trick, though it was MySQL specific. It can also be used in Yii 2:

Solution 1 : GROUP BY ¶

$authors = Author::find()
    ->joinWith('posts')
    ->where(['like', 'post.title', $searchword])
    ->groupBy('author.id')
    ->orderBy(['author.name' => SORT_ASC])
    ->limit(5)
    ->all();

In this way we could remove the redundant rows by grouping the results by author's ID.

Solution 2 : DISTINCT ¶

You may say "Why don't you use DISTINCT? It might be cleaner and more compatible than a dirty trick." Seems fairly reasonable. Let's give it a try:

$authors = Author::find()
    ->distinct()
    ->joinWith('posts')
    ->where(['like', 'post.title', $searchword])
    ->orderBy(['author.name' => SORT_ASC])
    ->limit(5)
    ->all();

Huh, done!

We are going to the last task, feeling a bit confused by the unexpected easiness.

Task 8: LIMIT and ORDER, with Relevant Relations ¶

Show top 5 authors ordered by name who has a post that has a certain word in post title, with all of their relevant posts

Now it's a simple task. You just have to apply the same filter both for the searching of the main models and the loading the related models.

Example of a Solution ¶

$authors = Author::find()
    ->distinct()
    ->joinWith([
        'posts' => function($query) use ($searchword) {
            $query->where(['like', 'post.title', $searchword]);
        },
    ])
    ->orderBy(['author.name' => SORT_ASC])
    ->limit(5)
    ->all();

Thus we finish the drills in an anticlimactic end.

Summary ¶

Fantastic, isn't it?

Reference ¶

Please refer to the database sections of the guide.

• The Definitive Guide to Yii 2.0
  • Query Builder and Query
  • Active Record