Laravel Validation against Unique Values

I would like to create a validation for the update function I would like it to exclude the title for that dedant id

  public function update(Request $request, Post $post)
    {
      $this->validate($request,[
         'title' => "required|unique:posts,title,".$id.'id',
         'image' => 'image',
         'categories' => 'required',
         //'tags' => 'required',
         'body' => 'required',
     ]);

via Chebli Mohamed