Contact Form 7 - Custom Validation

Question

I need to validate just one field (called 'Instance') to accept lowercase ASCII letters and numbers only, the first character also has to be a letter not a number. It will accept uppercase characters but we will need it to lowercase them on input. So if someone uses the instance name McDonalds it will be lowercased to mcdonalds (not just with CSS). Spaces are not allowed either.

Is this possible with CF7? If so please explain how.

I've already tried this custom validation method but even with the preset custom validation in the file it was just displaying the field shortcode rather than the field itself.

Thanks

Answer 1

From contactform7.com on Custom Validation → Validation as a Filter:

In Contact Form 7, a user-input validation is implemented as a filter function. The filter hook used for the validation varies depending on the type of form-tag and is determined as: wpcf7_validate_ + {type of the form-tag}. So, for text form-tags, the filter hook wpcf7_validate_text is used. Likewise, wpcf7_validate_email* is used for email* form-tags.

Let’s say you have the following email fields in a form:

  Email:         [email* your-email]
  Confirm email: [email* your-email-confirm]

The following listing shows code that verifies whether the two fields have identical values.

add_filter('wpcf7_validate_email*', 'custom_email_confirmation_validation_filter', 20, 2);

function custom_email_confirmation_validation_filter($result, $tag) {
    $tag = new WPCF7_FormTag($tag);

    if ('your-email-confirm' == $tag->name) {
        $your_email = isset($_POST['your-email']) ? trim($_POST['your-email']) : '';
        $your_email_confirm = isset($_POST['your-email-confirm']) ? trim($_POST['your-email-confirm']) : '';

        if ($your_email != $your_email_confirm) {
            $result->invalidate($tag, "Are you sure this is the correct address?");
        }
    }
    return $result;
}

Two parameters will be passed to the filter function: $result and $tag. $result is an instance of WPCF7_Validation class that manages a sequence of validation processes. $tag is an associative array composed of given form-tag components; as you saw in the previous recipe, you can use WPCF7_FormTag class to handle this type of data.

Look through the inside of the filter function. First, check the name of the form-tag to ensure the validation is applied only to the specific field (your-email-confirm).

The two email field values are then compared, and if they don’t match, $result->invalidate() will be called. You need to pass two parameters to the invalidate() method: the first parameter should be the $tag variable, and the second parameter is the validation error message that you want the field to display.

Lastly, don’t forget to return the $result.