Zend\Input and empty values

I’m forever getting confused about how the combination of Zend\Input‘s required, allow_empty & continue_if_empty interact with an empty value, so I’ve decided to write it down.

These settings define what happens when you try to validate an empty value for a given input. For Zend\Input, empty means exactly equal to null, an empty string or an empty array.

Firstly, let’s start with the three settings:

Firstly, contine_if_empty controls if the validators are run for an empty value. If contine_if_empty is true, then the validators are always executed.

If contine_if_empty is false, then the decision on whether to run the validators depends on the combination of required and allow_empty:

Test app

To prove this, I wrote this little test app:

 ?php
require 'vendor/autoload.php';

$values = [
    // [contine_if_empty, required, allow_empty]
    [false, true, false],
    [false, true, true],
    [false, false, false],
    [false, false, true],
    [true, true, false],
    [true, true, true],
    [true, false, false],
    [true, false, true],
];

foreach ($values as $row) {
    test(...$row);
}

function test($continueIfEmpty, $required, $allowEmpty)
{
    // set up Input with a StringLength validator so we'll know if the
    // validators have run as they will always fail
    $name = new \Zend\InputFilter\Input('name');
    $validators = $name->getValidatorChain();
    $validators->addValidator(new \Zend\Validator\StringLength(5), true);
    $name->setValue('');

    $name->setRequired($required);
    $name->setAllowEmpty($allowEmpty);
    $name->setContinueIfEmpty($continueIfEmpty);

    // Test
    echo "continue_if_empty: " . (int)$continueIfEmpty;
    echo ", required: " . (int)$required;
    echo ", allow_empty: " . (int)$allowEmpty;
    $isValid = (int)$name->isValid();
    echo " - Result: isValid() = $isValid";
    if (!$isValid) {
        echo " " . current($name->getMessages());
    }
    echo "\n";
}

You’ll need to run composer require zendframework/zend-inputfilter if you want to test it yourself.

Interesting side note: I got to use the splat operator, so this is PHP 5.6 only code :)

The test is quite simple. We add a StringLength validator to an input so that we know that the validators have run as it will always fail. We then iterate through all the the combinations of required, allow_empty & continue_if_empty and see what happens.

The output is:

$ php test.php 
continue_if_empty: 0, required: 1, allow_empty: 0 - Result: isValid() = 0 Value is required and can't be empty
continue_if_empty: 0, required: 1, allow_empty: 1 - Result: isValid() = 1
continue_if_empty: 0, required: 0, allow_empty: 0 - Result: isValid() = 1
continue_if_empty: 0, required: 0, allow_empty: 1 - Result: isValid() = 1
continue_if_empty: 1, required: 1, allow_empty: 0 - Result: isValid() = 0 The input is less than 5 characters long
continue_if_empty: 1, required: 1, allow_empty: 1 - Result: isValid() = 0 The input is less than 5 characters long
continue_if_empty: 1, required: 0, allow_empty: 0 - Result: isValid() = 0 The input is less than 5 characters long
continue_if_empty: 1, required: 0, allow_empty: 1 - Result: isValid() = 0 The input is less than 5 characters long

Conclusion

The interactions between required, allow_empty & continue_if_empty aren’t that complicated, but there’s enough complexity that it’s worth having a reference handy!