0039-one-to-many.md

One-to-Many relations

An example one-to-many relation diagram:

Database design

With one-to-many relation, 1 record from first table (eg. blog_posts) has zero or more matching records on the other table (eg. comments).

One of the tables needs to have a column that will hold the id of the record on the other table.

In our example, we have blog_posts and comments. BlogPost can be related to 1, 2, 3...n Comment, so the relation has to be stored inside Comment.

In short:

• has* - methods on Models that own the relation, no relation column
• belongs* - methods on Models that are other side of the relation, with relation column

In the example above each BlogPost model has zero or more Comment.

Defining relations

The relation on BlogPost model:

class BlogPost extends Model
{
    public function comments()
    {
        return $this->hasMany('App\Comment');
    }
}

Relation on Comment model:

class Comment extends Model
{
    public function blogPost()
    {
        return $this->belongsTo('App\BlogPost');
    }
}

Migrations

BlogPost already exists and requires no changes.

Comment model migration:

Schema::create('comments', function (Blueprint $table) {
    $table->increments('id');
    $table->timestamps();
    $table->string('content');

    $table->unsignedInteger('blog_post_id')->index();
    $table->foreign('blog_post_id')->references('id')->on('blog_posts');
});