Detailed introduction to related knowledge of Laravel model association deletion

Laravel is a popular PHP framework with powerful ORM (Object Relational Mapping) functionality that makes data manipulation easier. In Laravel, we can use model associations to implement connections and operations between data tables.

But sometimes, we need to delete a certain model association, so we need to use Laravel's model association deletion. Below, this article will introduce in detail the relevant knowledge of Laravel model association deletion.

Establish model association

Before introducing the deletion of model association, let’s first understand how to establish model association. Taking the one-to-many relationship as an example, in Laravel, we can use the hasMany and belongsTo methods to establish model relationships.

// User 模型
class User extends Model
{
    public function posts()
    {
        return $this->hasMany(Post::class);
    }
}

// Post 模型
class Post extends Model
{
    public function user()
    {
        return $this->belongsTo(User::class);
    }
}

In the above code, the User model and the Post model establish a one-to-many relationship. The User model uses the hasMany method to define an association with the Post model, and the Post model uses the belongsTo method to define an association with the User model.

After that we can use these relationships to operate data. For example, we can use the following code to obtain all articles of a user:

$user = User::find(1);
$posts = $user->posts;

Here, we obtain all articles of a user through the posts method of the User model. Since the User model and the Post model have a one-to-many relationship, $user->posts returns a Post model collection containing all the posts of the user.

Delete model association

For one-to-many relationships, we can use unset or null to delete the association. For example, the following code will delete all articles of a user:

$user = User::find(1);
$user->posts()->delete();

In the above code, we use the $user->posts() method to obtain all article associations of the user, and then call delete method to delete it.

For many-to-many relationships, we can use the detach method to delete the association. For example, the following code will delete an article from a user's watch list:

$user = User::find(1);
$post = Post::find(1);

$user->posts()->detach($post->id);

In the above code, we use the $user->posts() method to obtain a user's watch list association relationship, and then use the detach method to delete one of the articles. The parameter of the detach method is the id of the article.

Cascade Delete

In some special cases, we may need to delete its association relationship when deleting a model. At this time, we can use Laravel's cascade delete function.

For one-to-many relationships, we can use the onDelete('cascade') method to implement cascade deletion. For example, the following code will delete all articles of a user when deleting it:

// User 模型
class User extends Model
{
    public function posts()
    {
        return $this->hasMany(Post::class)->onDelete('cascade');
    }
}

In the above code, we define cascade deletion using the onDelete('cascade') method. This way, when a user is deleted, all articles associated with that user will also be deleted.

For many-to-many relationships, we can use the detach method to implement cascade deletion. For example, the following code will delete all articles using that tag when deleting it:

// Post 模型
class Post extends Model
{
    public function tags()
    {
        return $this->belongsToMany(Tag::class)->withTimestamps();
    }
}

// Tag 模型
class Tag extends Model
{
    public function posts()
    {
        return $this->belongsToMany(Post::class)->withTimestamps()->onDelete('cascade');
    }
}

In the above code, we define cascade deletion using the onDelete('cascade') method. In this way, when a tag is deleted, all articles using that tag will be deleted.

Summary

Laravel’s ORM function is very powerful and can easily implement relationship operations between models. When deleting model associations, we can use unset, null, detach, onDelete('cascade') and other methods to delete the association. At the same time, cascade deletion is also a very useful function, which can avoid manually deleting related data one by one.

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