Understanding `required` and `allowEmpty` in CakePHP validation rules

Posted by on June 03, 2013 · 4 mins read

One of the most confusing things about CakePHP’s validation rules is the meaning of the required and (especially) allowEmpty flags. Therefore I figured I’d give them both a quick walkthrough that you can reference whenever you get confused.

So here are some important facts about Cake validation rules, in bullet points:

  • Validation rules for ields that are not specified in the fieldList for a Model::validates() or Model::save() call are never executed; these fields will not be saved so they are completely ignored. The allowEmpty/required flags will not change this behavior.

  • required and allowEmpty only affect whether a validation rule is executed or not. They do not affect the rule itself, they are merely meant as an easy way to break out of common scenarios without having to add extra rules.

  • Now that we’ve established that; required only checks whether a field is present on the input array using array_key_exists. If the field is not present, the validation rules for this field are not executed, because you cannot use the value of a field that doesn’t exist. With required = true in this scenario the validation rule will fail with the message of the rule the required flag was set on, while required = false would lead to the field’s validation succeeding without any rule being executed. The default value of required is false, meaning a field doesn’t have to be present with the save.

  • The allowEmpty flag lets you skip all validation rules for a field or fail immediately if the field is left empty. This empty check is defined true for any value for which empty returns true, except for "0", which is considered non-empty. Now comes the confusing part: allowEmpty has three possible values, not two. Specifying true would cause validation to be skipped if the field is empty, specifying false causes it to fail in that case. You might already see the missing third case here: the one that skips the empty check and just executes the validation rule. This is actually the default behavior - it happens when you don’t specify allowEmpty at all. The explicit equivalent of this would be allowEmpty = null.

I hope this settles some of the confusion.

One more thing though: sometimes you want a different validation error for when a field has not been specified but should have been - this is impossible when adding required = true to an existing rule (because that rule has its own validation error). The solution is adding a validation rule that always succeeds to your model:

// The validation rules
public $validate = array(
	'fieldName' => array(
		'required' => array(
			'rule' => 'present',
			'message' => 'This field is required',
			'required' => true
		'some_other_rule' => array(
			'rule' => 'whatever',
			'message' => 'Some other condition is not met'

// The rule
public function present() {
	return true;

This way validation will fail with a "This field is required" error if it is left out, and another appropriate error if a different condition fails.