Answers for "laravel self referencing foreign key"

laravel foreign key constraint

public function up()
{
    Schema::create('replies', function (Blueprint $table) {
        $table->bigIncrements('id');
        $table->text('body');
        $table->unsignedBigInteger('question_id');
        $table->integer('user_id')->unsigned();
        $table->foreign('question_id')->references('id')->on('questions')->onDelete('cascade');
        $table->timestamps();
    });
}

eloquent self foreign key

class User extends Eloquent {

    protected $table = 'users';
    public $timestamps = false;

    public function parent()
    {
        return $this->belongsTo('User', 'parent_id');
    }

    public function children()
    {
        return $this->hasMany('User', 'parent_id');
    }

}