Yii2 join relations for multiple tables - php

Question

I am new to yii2. I have read the documentation and some answers on sof but still I cant get to work with relations in yii2. I am able to create raw mysql query for the problem but I dont know how to create the same query using yii2 relations. I am confused with via, joinWith and some key concepts. I will make the problem as descriptive as possible.
I have four models.
Category, CategoryNews, NewsTags, Tags
category table - cat_id, cat_name
news_category table - nc_id, nc_cat_id, nc_news_id
news_tags table - nt_id, nt_news_id, nt_tag_id
tags table - tag_id, tag_name
What I need is tags model object for each category, that is for each category i need all news tags belonging to that category. Request is from gridview.
The generated relations are:
Category Model:
public function getNewsCategory()
{
return $this->hasMany(NewsCategory::className(), ['nc_cat_id' => 'cat_id']);
}
NewsCategory Model:
public function getNcNews()
{
return $this->hasOne(News::className(), ['news_id' => 'nc_news_id']);
}
public function getNcCat()
{
return $this->hasOne(Category::className(), ['cat_id' => 'nc_cat_id']);
}
NewsTags Model:
public function getNtNews()
{
return $this->hasOne(News::className(), ['news_id' => 'nt_news_id']);
}
public function getNtTag()
{
return $this->hasOne(Tags::className(), ['tag_id' => 'nt_tag_id']);
}
News Model:
public function getNewsCategory()
{
return $this->hasMany(NewsCategory::className(), ['nc_news_id' => 'news_id']);
}
public function getNewsTags()
{
return $this->hasMany(NewsTags::className(), ['nt_news_id' => 'news_id']);
}
Tags Model:
public function getNewsTags()
{
return $this->hasMany(NewsTags::className(), ['nt_tag_id' => 'tag_id']);
}
ie. each category contains multiple news and each news contain mutiple tags and I need all tags related to each category.
More precisely, on the gridview I need all categories and a column displaying all tags related to these categories.
Please help!!

Answer 1

You can avoid declaration of models for junction tables, using viaTable syntax for many-to-many relations. Then your code will contain only three models (Category, News and Tag) and everything will be much simplier.
Your code for AR models and relations could looks as follows:
public class Category extends ActiveRecord
{
public function getNews()
{
return $this->hasMany(News::className(), ['id' => 'news_id'])
->viaTable('news_category_table', ['category_id' => 'id']);
}
}
public class News extends ActiveRecord
{
public function getCategories()
{
return $this->hasMany(Category::className(), ['id' => 'category_id'])
->viaTable('news_category_table', ['news_id' => 'id']);
}
public function getTags()
{
return $this->hasMany(Tags::className(), ['id' => 'tag_id'])
->viaTable('news_tags_table', ['news_id' => 'id']);
}
}
public class Tag extends ActiveRecord
{
public function getNews()
{
return $this->hasMany(News::className(), ['id' => 'news_id'])
->viaTable('news_tags_table', ['tag_id' => 'id']);
}
}
These relations you can use in link and unlink functions (rows in junction tables will be managed by Yii in backround). But keep in mind that you should use TRUE as second param in unlink() to remove row in junction table:
$article = new News();
$tag = new Tag();
$tag->save();
$article->link('tags', $tag);
$article->link('caterories', $category);
OR vice versa
$tag->link('news', $article);
$category->link('news', $article);
To get all tags in given category you can declare following function in Category class:
public function getTags()
{
return Tags::find()
->joinWith(['news', 'news.categories C'])
->where(['C.id' => $this->id])
->distinct();
}
This will work as relation query and you can use it as $category->tags or as $category->getTags()->count() or any other way (but not in link and unlink functions).
P.S. To use provided example in your code You should first change names, because I used singular form for AR classes names (Tag) and short notation for primary and foreign keys (id, tag_id etc). And I'd recommend you also to use such naming approach in your code and DB structure.
P.P.S. This example code wasn't tested so be careful :)