In actual development, we often come into contact with several common correspondence patterns:
One-To-One //一对一 One-To-Many //一对多 Many-To-Many //多对多
When I first came into contact with these concepts, I actually didn’t quite understand them. But once you apply these concepts to life, it's easy to understand. Let's take an example that we often see online:
User-To-Profile // One-To-One User-To-Articles // One-To-Many Articles-To-Tags // Many-To-Many
translates to:
- One user corresponds to one user profile
- A user can publish multiple articles
- There is a many-to-many relationship between articles and tags. An article can have multiple tags; a tag can belong to Multiple articles
Among these relationship models, the most difficult to implement is the many-to-many relationship Many-To-Many, but with the help of Laravel’s powerful Eloquent, it is quite satisfying to implement this function.
1. Create database table
Createarticlestable
Schema::create('articles', function (Blueprint $table) {
$table->increments('id');
$table->string('title');
$table->text('content');
$table->timestamps();
});
Createtagstable
Schema::create('tags', function (Blueprint $table) {
$table->increments('id');
$table->string('name');
$table->timestamps();
});
Of course , to solve this classic problem, these two tables alone are not enough. It is necessary to establish a relationship table in addition to these two tables to connect article and tag. In Laravel, if you follow the official standard rules, the third table should look like this:
Table namearticle_tag
Schema::create('article_tag', function(Blueprint $table) {
$table->integer('article_id')->unsigned()->index();
$table->foreign('article_id')->references('id')->on('articles')->onDelete('cascade');
$table->integer('tag_id')->unsigned()->index();
$table->foreign('tag_id')->references('id')->on('tags')->onDelete('cascade');
});
If you do not follow the official specifications Now, you need to specify the foreign key in the model.
2. Create the model and specify the relationship
In Article.php:
<code><br> public function tags()
{
return $this->belongsToMany('App\Tag');
}</code>
In Tag.php:
public function articles()
{
return $this->belongsToMany('App\Article');
}
Note two points here:
- You can specify foreign keys when declaring the relationship, such as
$this->belongsToMany('App\Article',' foreign_key', 'other_key'); - If you add timestamps() in the article_tag table, that is, the two fields created_at and updated_at appear in the table, you need to do this when declaring the relationship in Article ：
return $this->belongsToMany('App\Tag')->withTimestamps();
Controller ## If we want to check which tags an article contains, we can do this:
$article = Article::find($id); dd($article->tags);
If we want to find an article by a certain tag:
<code><br>public function showArticleByTagName($name)
{
$tag = Tag::where('value','=',$name)->first();
dd($tag->articles);
}</code>
The above is achieved.
Many-To-Many. in Laravel
