How to enforce a unique field value for each form entry

Created by Phil Kurth, Modified on Mon, 4 Jul, 2022 at 2:34 PM by Phil Kurth

If you come across a situation where you need each form entry to submit a unique value — e.g; one entry per email address — you may use the af/form/before_submission hook.

To do so, you need to look up existing entries for the given form with a value matching the submitted value for a given field. If an entry is found, simply add a submission error to Advanced Forms using the af_add_submission_error() function. The form won't submit and the error message will be displayed to the user.

// Prevent a form from submitting if there is already a form entry containing the same value in a specific field.
add_action( 'af/form/before_submission', function ( $form, $fields, $args ) {
  // Configure these accordingly.
  $form_key = 'YOUR_FORM_KEY_HERE';
  $field_name = 'email';

  // Only run on a specific form.
  if ( $form['key'] !== $form_key ) {
    return;
  }

  // Get the value from the submission to compare against.
  $submitted_value = af_get_field( $field_name );

  // See if we already have an entry for the given form from the email address.
  $entries = get_posts( [
    'post_type' => 'af_entry',
    'posts_per_page' => '-1',
    'meta_query' => [
      [
        'key' => 'entry_form',
        'value' => $form_key,
      ],
      [
        'key' => $field_name,
        'value' => $submitted_value,
      ]
    ],
  ] );

  // If one or more entries are found matching the criteria, add a submission error.
  if ( ! empty( $entries ) ) {
    af_add_submission_error( "'$field_name' must be unique. There is already an entry with the value '$submitted_value'." );
  }
}, 10, 3 );