functions.php

add_filter( 'gform_pre_render_9', 'uri_interested_property' );
add_filter( 'gform_pre_validation_9', 'uri_interested_property' );
add_filter( 'gform_pre_submission_9', 'uri_interested_property' );
add_filter( 'gform_admin_pre_render_9', 'uri_interested_property' );
/**
 * Dynamically builds Gravity Fields dropdown for Property of Interest form field
 *
 * @param $form
 *
 * @return mixed
 */
function uri_interested_property( $form ) {

    foreach ( $form['fields'] as &$field ) {

        //* Only interested in dropdowns with the 'uri_interested_property' class
        if ( $field->type != 'select' || strpos( $field->cssClass, 'uri_interested_property' ) === false ) {
            continue;
        }

        global $wpdb;

        //* Select property addresses from post meta
        $sql = "SELECT DISTINCT meta_value as address FROM wp_postmeta m, wp_posts p WHERE meta_key = '_zoner_address' && p.ID = m.post_id && p.post_status = 'publish' ORDER BY meta_value;";

        $posts = $wpdb->get_results( $sql );

        $choices = array();

        foreach ( $posts as $post ) {
            $choices[] = array( 'text' => $post->address, 'value' => $post->address );
        }

        $property_choices = array_map("unserialize", array_unique(array_map("serialize", $choices ) ) );

        $field->placeholder = 'Select a Property';
        $field->choices = $property_choices;

    }

    return $form;

}