Showing reverse relationships within admin

• cjke7777

• December 16, 2016 at 3:33 am

Is there a way to show the reverse relationship of a taxonomy relationship, namely for what would normally be considered a M2M relationship?

For example, lets say I have two custom post types, Movies and Genres.

1 – I add an ACF to Movies of type “Relationship” with “Post Filter” set to “Genres”.

2 – I create a movie – “Spiderman” and add two genres, “Action”, “Comic” via the admin panel.

3 – Via theme functions, in the frontend, I can display the genres belonging to Spiderman, and, conversely, in the frontend, I can display the movies belongs to “Action” or to “Comic”.

4 – The missing part – While in the admin area, can I show the movies belonging to a genre, while editing said genre.

Note I can add an ACF of type “Relationship” with “Post Filter” set to “Movies” in Genres as well – but they don’t marry up as it seems at the db level they maintain there own sense of metadata.

• James

• December 16, 2016 at 1:04 pm

Hi @cjke7777

In this case, you need to use the Bidirectional Relationships. You can check our tutorial here: https://www.advancedcustomfields.com/resources/bidirectional-relationships/.

I hope this helps 🙂

• cjke7777

• December 16, 2016 at 1:11 pm

I just read through the code, looks really good. The example shows post<->post, but I would imagine it could be applied to any custom type (being that they all “inherit” from post anyway, in that strange lovely way WP does things).

One follow up question – with different types (like Movie + Genre), would you add the Relationship ACF to both the movie and the genre for the above snippet to work correctly?

As a sidenote, and in hindsight, I realise genre is really a poor example (ie could be taxonomy, but just an example 🙂 )

• James

• December 16, 2016 at 1:40 pm

Hi @cjke7777

Yes, I believe you need to add the relationship to both of the post types to make it works.

• cjke7777

• December 16, 2016 at 1:42 pm

Cool I will try it out in the next few hours and leave an update here to confirm either way for future readers. Thanks for help, I will touch base shortly

• cjke7777

• December 16, 2016 at 4:47 pm

Ok so yep it seems like you need a relationship field in both. I’m not totally comfortable with storing the relationship twice – I feel like thats a sleeper-bug waiting to happen.

ie:
– Movie A stores thats it is GenreA, GenreB, and
– GenreA stores (separately) that is has Movie A
– GenreB stores (separately) that is has Movie A

So, as a compromise, for each relation, I nominate one as the relationship owner and only it can edit the relationship. And for the non-relationship owner I have added the following meta box which will list all possible relations.

// Helper to grab all possible post types that could contain relationships
if (! function_exists('get_content_post_types')) {
    function get_content_post_types() {
        return array_merge(
            ['page', 'post'],
            array_values(get_post_types([ '_builtin' => false ]))
        );
    }
}

// Create a query that finds our parent id in the serialised array
if (! function_exists('acf_find_parents')) {
    function acf_find_parents($id, $fields) {
        return new \WP_Query([
            'post_type' => get_content_post_types(),
            'meta_query' => [
                'relation' => 'OR',
                array_map(function($field) use ($id) {
                    return [
                        'key'       => $field,
                        'value'     => '"' .$id. '"',
                        'compare'   => 'LIKE'
                    ];
                }, $fields),
            ]
        ]);
    }
}

And then the usage would be something like:

// Inside the genre page
// This would find all times that this post has existed in anothers relation
acf_find_parents($post->ID, ['music', 'movies', 'books']);

An example of formatting this nicely would be:

// Using laravels collect methods
add_action('add_meta_boxes', function() {
    add_meta_box('genre_relationships', 'Relationships', function($post) {
        collect(acf_find_parents($post->ID, ['music', 'movies'])->posts)
            ->groupBy('post_type')
            ->each(function($type, $key) {
                echo "<h3>{$key}</h3>";
                $type->each(function($related) {
                    echo "<div>{$related->post_title}</div>";
                });
            });
    });
});

This would spit out:

music
song G
song F
movies
movie A
movie C

Again, its a bit of a compromise, but I would prefer this over duplicating the data.

Disclaimer: The query probably should extend to join against the post table to make the post_type is actually a acf field