How to get foreign key from eloquent collection in laravel

I have hasMany relationship in my User model;

 /**
 * Get the posts for the users.
 */
public function posts()
{
    return $this->hasMany(Posts::class); //foreign key assigned by user_id
}

I need to get a foreign id in Eloquent data

Controller;

use AppModelsUser;

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

foreach ($posts as $post) {
    //
}
//for example
$foreign_key = $posts->foreign_key;
echo "all posts collection assigned foreign key is; ".$foreign_key;

Expected output;

1

How can I get the foreign key?

Answer

You can do the following. Since posts has hasmany relation so it return collection of object even though you have one item in posts.

foreach ($posts as $post) {
     
    echo $post->user_id;
}

or

 dd($posts->first()->user_id);

If you still need one item from posts relationship then you can add one relationship

public function post()
{
    return $this->hasOne(Posts::class); //foreign key assigned by user_id
}

then you can access

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

$foreign_key =$posts->user_id;