Conditional rules validation and compare values

I have users register and provide Role below


echo $this->Form->create($user) ;
//...more field ...
echo $this->Form->radio(
	    ['value' => 'Administrator', 'text' => 'Administrator'],
	    ['value' => 'Penulis Artikel', 'text' => 'Penulis Artikel'],
	    ['value' => 'Pengunjung', 'text' => 'Pengunjung'],
//...more field
echo $this->Form->submit('TAMBAH');
echo $this->Form->end();

next I have provide conditional rules and both compare,


namespace App\Model\Table;

use Cake\ORM\Query;
use Cake\ORM\RulesChecker;
use Cake\ORM\Rule\IsUnique;
use Cake\ORM\Table;
use Cake\Validation\Validator;

class UsersTable extends Table
   public function buildRules(RulesChecker $rules)
      $rules->add(function ($entity, $options) use($rules) {
		     if ($entity->Role == 'Administrator') {
			  $rule = $rules->existsIn('User', 'Administrator');
			  return $rule($entity, $options);
		     return false;
	         }, 'Administrator tidak boleh lebih dari 1');
		 return $rules;

the conditional rules inside (UsersTable) that I want output is compare field values Role == Administrator, not greater than one.
the error messages shown is

ExistsIn rule for 'User' is invalid. 'Administrator' is not associated with 'App\Model\Table\UsersTable'.

I hope someone help me to fix error, thanx

The first argument to existsIn is the column name where the value to check is found in the entity. Does your entity have a column called User?

The second argument is the associated table to look up the value in. Does your UsersTable have an association called Administrator?

here structure UsersTable in mysql

|  Nama    |      Role              |      Dibuat           |        Diubah        |       Aksi                |  
|  Budi    |   Administrator        |  04-04-2019 14:33:29  |                      |   Tampil  Perbarui  Hapus |

the rule validation inside UsersTable.php, that’s I want, is prevent add new user with Role = Administrator, more than one,…simply is Role = Administrator just only one users.

I’m tired after reading in

that’s hard to understand.
I home someone can help me,…thanx

existsIn is to make sure that a value exists in another table. For example, if you’re adding a post with a user id, to confirm that the user id is for a real user. Seems that you’re not looking to cross-reference another table here, so existsIn is not at all the right thing. Sounds like you want something more like:

if ($entity->Role == 'Administrator' &&
    $this->find()->where(['Role' => 'Administrator'])->count() != 0)
    return false;