Cómo relacionar dos tipos de post sin necesidad de taxonomía | Relación bidireccional

¡Al fin lo logré! En breve actualizo esta nota para explicar al detalle la búsqueda que más tiempo me ha llevado.

De momento dejo aquí el enlace para quien quiera ir chusmeando:

This tutorial will cover the concept and code for creating a bidirectional relationship between posts using only the Advanced Custom Fields plugin.

Origen: ACF | Bidirectional Relationships

 

 

function bidirectional_acf_update_value( $value, $post_id, $field ) {
// vars
$field_name = $field['name'];
$field_key = $field['key'];
$global_name = 'is_updating_' . $field_name;

// bail early if this filter was triggered from the update_field() function called within the loop below
// - this prevents an inifinte loop
if( !empty($GLOBALS[ $global_name ]) ) return $value;

// set global variable to avoid inifite loop
// - could also remove_filter() then add_filter() again, but this is simpler
$GLOBALS[ $global_name ] = 1;

// loop over selected posts and add this $post_id
if( is_array($value) ) {
foreach( $value as $post_id2 ) {
// load existing related posts
$value2 = get_field($field_name, $post_id2, false);

// allow for selected posts to not contain a value
if( empty($value2) ) {
$value2 = array();
}

// bail early if the current $post_id is already found in selected post's $value2
if( in_array($post_id, $value2) ) continue;

// append the current $post_id to the selected post's 'related_posts' value
$value2[] = $post_id;

// update the selected post's value (use field's key for performance)
update_field($field_key, $value2, $post_id2);
}
}

// find posts which have been removed
$old_value = get_field($field_name, $post_id, false);
if( is_array($old_value) ) {
foreach( $old_value as $post_id2 ) {
// bail early if this value has not been removed
if( is_array($value) && in_array($post_id2, $value) ) continue;

// load existing related posts
$value2 = get_field($field_name, $post_id2, false);

// bail early if no value
if( empty($value2) ) continue;

// find the position of $post_id within $value2 so we can remove it
$pos = array_search($post_id, $value2);

// remove
unset( $value2[ $pos] );

// update the un-selected post's value (use field's key for performance)
update_field($field_key, $value2, $post_id2);
}
}

// reset global varibale to allow this filter to function as per normal
$GLOBALS[ $global_name ] = 0;

// return
return $value;
}
add_filter('acf/update_value/name=related_posts', 'bidirectional_acf_update_value', 10, 3);
add_filter('acf/update_value/name=related_places', 'bidirectional_acf_update_value', 10, 3);