get_posts empty when called via Ajax

Question

What would cause a basic get_posts() query to return an empty array during an Ajax function?

I have a front end page which loads a form. There is a dropdown which is populated when the page loads with some post titles. The same function that populates the select list values is called via Ajax when the value of another select list changes.

When the function is called via Ajax, the result is an empty array. When the page loads, the select list is fully populated.

By usingerror_log( var_export( $args, true ), 0 ); I have confirmed that the arguments passed to the function are the same on both page load and Ajax call and with error_log( var_export( $addons, true ), 0 ); I confirmed results on page load and an empty array on Ajax call. This also confirms execution of the correct function via Ajax.

/**
 * Retrieve all addons.
 *
 * @since   1.4
 * @param   arr         $args   Array of arguments. See @get_posts.
 * @return  arr|bool    Addons.
 */
function mh_get_addons( $args = array() )   {

    $defaults = array(
        'posts_per_page' => -1,
        'orderby'        => 'post_title',
        'order'          => 'DESC',
        'post_type'      => 'mh-addon',
        'post_status'    => 'publish'
    );

    $args = wp_parse_args( $args, $defaults );
    error_log( var_export( $args, true ), 0 );
    $addons = get_posts( $args );
    error_log( var_export( $addons, true ), 0 );
    return apply_filters( 'mh_get_addons', $addons );

} // mh_get_addons

Here is the Ajax function. As you can see I am passing no args here whilst testing so I would expect to see the same results I do on the initial page load.

function mh_update_form_addon_options() {

    $addons = mh_get_addons();

    if ( ! empty( $addons ) )   {
        $result['type']   = 'success';
        $result['addons'] = $addons;
    } else  {
        $result['type']   = 'success';
        $result['addons'] = 'No addons';
    }

    echo json_encode( $result );

    die();
} // mh_update_form_addon_options
add_action( 'wp_ajax_mh_update_form_addon_options', 'mh_update_form_addon_options' );
add_action( 'wp_ajax_nopriv_mh_update_form_addon_options', 'mh_update_form_addon_options' );

`

UPDATE The function is now returning results via the Ajax call when a user is logged in. However, if not logged in, no results. Strange thing is that the initial call to the mh_get_addons() function which is initiated on page load without ajax returns results regardless of whether or not a user is logged in...

Answer 1

To get data from AJAX call you have to echo or print it. In WordPress you should use wp_send_json() function to send data as response to call.

function mh_get_addons( $args = array() )   {

    $defaults = array(
        'posts_per_page' => -1,
        'orderby'        => 'post_title',
        'order'          => 'DESC',
        'post_type'      => 'mh-addon',
        'post_status'    => 'publish'
    );

    $args = wp_parse_args( $args, $defaults );
    $addons = get_posts( $args );
    wp_send_json( apply_filters( 'mh_get_addons', $addons ) );

} // mh_get_addons

Answer 2

Instead of using the WP AJAX API, have you tried registering a REST endpoint? This assumes at least WP 4.5:

add_action( 'rest_api_init', function () {
    register_rest_route( 'mike/v1', '/addons/', array(
        'methods' => 'GET',
        'callback' => 'mh_update_form_addon_options',
    ) );
} );


function mh_update_form_addon_options( WP_REST_Request $data ) {

    $defaults = array(
        'posts_per_page'   => 200,
        'orderby'          => 'post_title',
        'order'            => 'DESC',
        'post_type'        => 'mh-addon',
        'post_status'      => 'publish',
        'suppress_filters' => false
    );

    $addons = get_posts( $args );
    $result = array();    
    if ( empty( $addons ) )   {
        return new WP_Error("No addons");
    }

    return $addons;
}

I've also simplified the function and eliminated some uncertainty by removing filters. I've also sped up the get_posts call by setting suppress_filters to false so that it caches the result. I've also added a maximum number, if you somehow ended up with 1 million addons this request would always fail, so always set an upper limit, even if it's a silly number you know it'll never reach

Keep in mind in a REST endpoint, we return what we're sending, we don't echo it, and use WP_Error for problems. You can adjust the register_rest_route call to mention arguments, see the WP API documentation for how.

Only WP Core is needed for this, no WP API plugin necessary

Answer 3

Have you tried calling the global $post object at the top of your mh_get_addons() function?

function mh_get_addons( $args = array() )   {

  global $post;

  $defaults = array(
      'posts_per_page' => -1,
      'orderby'        => 'post_title',
      'order'          => 'DESC',
      'post_type'      => 'mh-addon',
      'post_status'    => 'publish'
  );

  $args = wp_parse_args( $args, $defaults );
  error_log( var_export( $args, true ), 0 );
  $addons = get_posts( $args );
  error_log( var_export( $addons, true ), 0 );
  return apply_filters( 'mh_get_addons', $addons );

  }

I'm not quite the wordpress expert yet, but had a similar issue when using get_posts($args) inside a function called via wp-ajax the way you call yours, and that solved it for me. Otherwise get_posts() wasn't able to retrieve any of the post information, hence the empty array you're seeing.