How do I do Laravel form validation when value of one field decides validity of the other field

I have a form. Type field is a drop-down and has only two possible values. Second field is bcode.
E.g. if table has data like-

ID  TYPE  BCODE
1     1     2
2     1     3
3     2     2
4     1     4
5     2     2

Now I am making a popup form to insert record in this table. So if type is entered 1 and bcode is entered 2,3 or 4 its already in table so it will be invalid but any other numeric value will be valid. Similarly if type is entered 2 then bcode can’t be anything other than 2,3 or 4. All other values will be invalid.

I read the Laravel docs here-
https://laravel.com/docs/6.x/validation#custom-validation-rules
But did not find anything.
Anyone tried something similar?

Answer

Assuming your table structure is like in your example and its called type_bcode, I’m offering the following solution:

1. Create custom rule by running php artisan make:rule TypeBcode
   It should look like this:

   private $type;
   
   public function __construct($type)
   {
       $this->type = $type;
   }
   public function passes($attribute, $value)
   {
       $type_bcode = DB::table('type_bcode')
           ->where('type', $this->type)
           ->get()
           ->pluck('bcode')
           ->toArray();
   
       return in_array($value, $type_bcode);
   }
   public function message()
   {
       return 'The validation error message.';
   }
   

2. In your controllers store function do this:

   public function store(Request $request)
   {
       $validator = Validator::make($request->all(), [
           'type' => 'required',
           'bcode' => ['required', new TypeBcode($request->type)],
       ]);
       if ($validator->fails()) {
           //some action
       }
       //some action
   }
   

Hope this will help