JSON API to show Advanced Custom Fields - WordPress

Question

I am developing a magazine WordPress site that will have a json feed for a Mobile App. I set the backend up using Advanced Custom Fields with a Repeater Field for Multiple Articles and Multiple Pages within each article. http://www.advancedcustomfields.com/add-ons/repeater-field/

I am using the JSON API but this does not include any of my custom fields. Is there currently a plugin that can do this?

Answer 1

@Myke: you helped me tremendously. Here's my humble addition:

add_filter('json_api_encode', 'json_api_encode_acf');


function json_api_encode_acf($response) 
{
    if (isset($response['posts'])) {
        foreach ($response['posts'] as $post) {
            json_api_add_acf($post); // Add specs to each post
        }
    } 
    else if (isset($response['post'])) {
        json_api_add_acf($response['post']); // Add a specs property
    }

    return $response;
}

function json_api_add_acf(&$post) 
{
    $post->acf = get_fields($post->id);
}

Answer 2

Update for Wordpress 4.7

With the release of Wordpress 4.7 the REST functionality is no longer provided as a distinct plugin, rather its rolled in (no plugin required).

The previous filters don't appear to work. However the following snippet does (can be in your functions.php):

>= PHP 5.3

add_filter('rest_prepare_post', function($response) {
    $response->data['acf'] = get_fields($response->data['id']);
    return $response;
});

< PHP 5.3

add_filter('rest_prepare_post', 'append_acf');

function append_acf($response) {
    $response->data['acf'] = get_fields($response->data['id']);
    return $response;
};

Note the filter is a wild card filter, applied like

apply_filters("rest_prepare_$type", ...

so if you have multiple content types (custom), you will need to do:

add_filter('rest_prepare_multiple_choice', 'append_acf');
add_filter('rest_prepare_vocabularies', 'append_acf');

function append_acf($response) {
    $response->data['acf'] = get_fields($response->data['id']);
    return $response;
};

Note It appears that rest_prepare_x is called per record. So if you are pinging the index endpoint, it will be called multiple times (so you don't need to check if its posts or post)