One-to-Many Relationships in Laravel Eloquent

One-to-many relationships allow a single model to own an unlimited number of related models, such as a blog post that can have many comments.

In an Eloquent model you define a method that returns $this->hasMany('App\Comment') . Laravel automatically determines the foreign key post_id by using the snake‑case form of the parent model name with an _id suffix.

<?php
namespace App;
use Illuminate\Database\Eloquent\Model;

class Post extends Model
{
    /**
     * Get the comments for the blog post.
     */
    public function comments()
    {
        return $this->hasMany('App\Comment');
    }
}
?>

After defining the relationship you can retrieve the comment collection via the dynamic comments property, e.g.:

$comments = App\Post::find(1)->comments;
foreach ($comments as $comment) {
    // process each comment
}

Because relationships are also query builders, you can chain additional constraints on the comments method:

$comment = App\Post::find(1)->comments()
    ->where('title', 'foo')
    ->first();

If you need to customize the foreign key or local key, you can pass them as extra arguments to hasMany :

return $this->hasMany('App\Comment', 'foreign_key');
return $this->hasMany('App\Comment', 'foreign_key', 'local_key');

Inverse One-to-Many (belongsTo)

To retrieve the parent model from a child, define a belongsTo method in the child model:

<?php
namespace App;
use Illuminate\Database\Eloquent\Model;

class Comment extends Model
{
    /**
     * Get the post that owns the comment.
     */
    public function post()
    {
        return $this->belongsTo('App\Post');
    }
}
?>

Now you can access the related post via the dynamic post property:

$comment = App\Comment::find(1);
echo $comment->post->title;

If the foreign key on the child model is not the default post_id , pass the custom key as the second argument to belongsTo . To use a different local key on the parent model, provide a third argument:

return $this->belongsTo('App\Post', 'foreign_key', 'other_key');

These conventions and customizations give you full control over how Laravel maps one-to-many relationships between tables.