Bug: Validation placeholder not being replaced

[nControl88]

Describe the bug
When using validation placeholders in a model and validating data, the placeholder is not being replaced with the actual data. The validation therefore returns false.

CodeIgniter 4 version
4.0.2

Expected behavior, and steps to reproduce if appropriate
Using the myth-auth package and the GroupModel. Validation rules are defined in the model as:

protected $validationRules = [
	'name' => 'required|max_length[255]|is_unique[auth_groups.name,name,{name}]',
	'description' => 'max_length[255]',
];

When trying to update a group in the controller using an already existing name in the database:

$groupModel = new GroupModel();

if (! $this->validate($rules = $groupModel->getValidationRules())) {
	return redirect()->back()->withInput()->with('errors', $groupModel->errors());
}

The validation returns false. Looking at the DB (MySQL) query ran it can be seen why:
SELECT 1 FROM `auth_groups` WHERE `name` = 'admin' AND `name` != '{name}' LIMIT 1

A manual replacement of {name} with the actual value resolves the issue.

[samsonasik]

i guess you are using postgresql, seems similar issue with my comment at #2812 (comment)

[nControl88]

After digging through the code I might have found the solution. This might also solve #2812.

In the Model class the validate() function includes a fillPlaceholders() before it sets the rules and runs the validation:

CodeIgniter4/system/Model.php

Lines 1434 to 1439 in 895f1e6

	// Replace any placeholders (i.e. {id}) in the rules with
	// the value found in $data, if exists.
	$rules = $this->fillPlaceholders($rules, $data);
	$this->validation->setRules($rules, $this->validationMessages);
	$valid = $this->validation->run($data, null, $this->DBGroup);

In the Controller class this call to fillPlaceholders() is not present:

CodeIgniter4/system/Controller.php

Lines 216 to 219 in 895f1e6

	return $this->validator
	->withRequest($this->request)
	->setRules($rules, $messages)
	->run();

When the fillPlaceholders() is added to the Controller class and called before the validator runs, the issue is solved:

// Replace any placeholders (i.e. {id}) in the rules with
// the value found in $data, if exists.
$rules = $this->fillPlaceholders($rules, $this->request->getVar());

$success = $this->validator
	->withRequest($this->request)
	->setRules($rules, $messages)
	->run();