missing-value.md

Handling Missing Values

The standard way to generate a ValidationResult representing a missing value is to call Phly\RuleValidation\Result\Result::forMissingValue(). That factory method produces a Result for the associated key, and uses the Result::MISSING_MESSAGE constant if no $message argument is provided. The Result it returns wraps a null value.

This might not be what you want. For instance, you might want to provide a more specific error message. Or you may want to ensure that the value associated is a valid empty value for the context (e.g., an empty string for a text input, or a DateTimeInterface instance for a date selector).

Customizing the message

The first thing you can do is to customize the associated message. As an example, in your Rule implementation, you could define the missing() method to do so:

public function missing(): Result
{
    return Result::forMissingValue(
        $this->key,
        'The "title" is a required value, but was not provided'
    );
}

Customizing the value

To customize the value, you can return a result representing an invalid value:

/** @return Result<DateTimeInterface> */
public function missing(): Result
{
    return Result::forInvalidValue(
        $this->key,
        new DateTimeImmutable(), // default value!
        'The creation date is a required value, but was not provided; select a valid date'
    );
}

The above returns a result that wraps a DateTimeInterface, and provides a custom message.

Return a custom ValidationResult

The third option is to return a custom ValidationResult implementation. Let's assume you have defined the class DateTimeResult such that it wraps a DateTimeInterface, and defines a forMissingValue() method that wraps a valid DateTimeInterface instance. You could then write the missing() implementation as follows:

public function missing(): DateTimeResult
{
    return DateTimeResult::forMissingValue(
        $this->key,
        'The creation date is a required value, but was not provided; select a valid date'
    );
}

Note that the return type hint has changed to represent the more specific type we are returning as well.

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