An ACF Relationship field with multisite support. Tested with ACF 6.3.6

acf-relationship-multisite.php

<?php

/**
 * An ACF Relationship field with multisite support. Tested with ACF 6.3.6 
 * 
 * This aims to be the lightest possible implementation of a multisite compatible relationship field.
 * For the php class we extend the existing ACF Relationship field and override the necessary methods.
 * 
 * For the JavaScript, we copy the existing ACF Relationship field and modify only the necessary properties.
 * 
 * There are minor CSS changes to the field type.
 * 
 * This code should be added to your theme's functions.php file.
 * 
 * add_action( 'acf/include_field_types', 'include_acf_relationship_multisite' );
 * function include_acf_relationship_multisite() {
 *   include_once('acf-relationship-multisite.php');
 * }
 * 
 * TODO
 * - Taxonomy filter only works for the current subsite. These should update as the blog_id filter changes.
 * - Comment where parts of php and js functions are different to the original relationship field.
 * - Document the returned field values.
 */

if (! class_exists('acf_field_relationship_multisite')) :

	class acf_field_relationship_multisite extends acf_field_relationship
	{


		/**
		 * This function will setup the field type data
		 *
		 * @type    function
		 * @date    5/03/2014
		 * @since   5.0.0
		 */
		public function initialize()
		{
			$this->name          = 'relationship_multisite';
			$this->label         = __('Relationship (multisite)', 'acf');
			$this->category      = 'relational';
			$this->description   = __('A multisite compatible variation of the relationship field.', 'acf');
			$this->preview_image = acf_get_url() . '/assets/images/field-type-previews/field-preview-relationship.png';
			$this->doc_url       = null;
			$this->defaults      = array(
				'post_type'            => array(),
				'taxonomy'             => array(),
				'min'                  => 0,
				'max'                  => 0,
				'filters'              => array('search', 'post_type', 'taxonomy', 'blog_id'),
				'elements'             => array(),
				'return_format'        => 'object',
				'bidirectional_target' => array(),
			);

			add_filter('acf/conditional_logic/choices', array($this, 'render_field_relation_conditional_choices'), 10, 3);

			// extra
			add_action('wp_ajax_acf/fields/relationship_multisite/query', array($this, 'ajax_query'));
			add_action('wp_ajax_nopriv_acf/fields/relationship_multisite/query', array($this, 'ajax_query'));
		}

		/**
		 * Returns a list of pretty subsites.
		 * 
		 * This function is similar to acf_get_pretty_post_types() and acf_get_pretty_taxonomies().
		 * 
		 * @param array $blog_ids
		 * @return array $r - an associative array of blog_id => blogname
		 */
		private function acf_get_pretty_subsites($blog_ids = array())
		{
			$blogs = get_sites();
			$r = array();
			foreach ($blogs as $blog) {
				if (!empty($blog_ids) && !in_array($blog->blog_id, $blog_ids)) {
					continue;
				}
				$r[$blog->blog_id] = $blog->blogname;
			}
			return $r;
		}

		/**
		 * Filters choices in relation conditions.
		 *
		 * @since 6.3
		 *
		 * @param array  $choices           The selected choice.
		 * @param array  $conditional_field The conditional field settings object.
		 * @param string $rule_value        The rule value.
		 * @return array
		 */
		public function render_field_relation_conditional_choices($choices, $conditional_field, $rule_value)
		{
			if (! is_array($conditional_field) || $conditional_field['type'] !== 'relationship_multisite') {
				return $choices;
			}
			if (! empty($rule_value)) {
				$post_title = get_the_title($rule_value);
				$choices    = array($rule_value => $post_title);
			}
			return $choices;
		}


		/**
		 * This function will return an array of data formatted for use in a select2 AJAX response
		 *
		 * @since   5.0.9
		 *
		 * @param array $options An array of options for the query.
		 * @return array
		 */
		public function get_ajax_query($options = array())
		{
			// defaults
			$options = wp_parse_args(
				$options,
				array(
					'post_id'   => 0,
					's'         => '',
					'field_key' => '',
					'paged'     => 1,
					'post_type' => '',
					'include'   => '',
					'taxonomy'  => '',
					'blog_id'   => '',
				)
			);

			// load field
			$field = acf_get_field($options['field_key']);
			if (! $field) {
				return false;
			}

			// vars
			$results   = array();
			$args      = array();
			$s         = false;
			$is_search = false;

			// paged
			$args['posts_per_page'] = 20;
			$args['paged']          = intval($options['paged']);

			// search
			if ($options['s'] !== '' && empty($options['include'])) {
				// strip slashes (search may be integer)
				$s = wp_unslash(strval($options['s']));

				// update vars
				$args['s'] = $s;
				$is_search = true;
			}

			// post_type
			if (! empty($options['post_type'])) {
				$args['post_type'] = acf_get_array($options['post_type']);
			} elseif (! empty($field['post_type'])) {
				$args['post_type'] = acf_get_array($field['post_type']);
			} else {
				$args['post_type'] = acf_get_post_types();
			}

			// post status
			if (! empty($options['post_status'])) {
				$args['post_status'] = acf_get_array($options['post_status']);
			} elseif (! empty($field['post_status'])) {
				$args['post_status'] = acf_get_array($field['post_status']);
			}

			// blog id
			if (! empty($options['blog_id'])) {
				// Add the blog_id to the args array - so that it can be filtered.
				$args['blog_id'] = $options['blog_id'];
			} elseif (! empty($field['blog_id'])) {
				$args['blog_id'] = $field['blog_id'];
			}

			// taxonomy
			if (! empty($options['taxonomy'])) {

				// vars
				$term = acf_decode_taxonomy_term($options['taxonomy']);

				// tax query
				$args['tax_query'] = array();

				// append
				$args['tax_query'][] = array(
					'taxonomy' => $term['taxonomy'],
					'field'    => 'slug',
					'terms'    => $term['term'],
				);
			} elseif (! empty($field['taxonomy'])) {

				// vars
				$terms = acf_decode_taxonomy_terms($field['taxonomy']);

				// append to $args
				$args['tax_query'] = array(
					'relation' => 'OR',
				);

				// now create the tax queries
				foreach ($terms as $k => $v) {
					$args['tax_query'][] = array(
						'taxonomy' => $k,
						'field'    => 'slug',
						'terms'    => $v,
					);
				}
			}

			if (! empty($options['include'])) {
				// If we have an include, we need to return only the selected posts.
				$args['post__in'] = array($options['include']);
			}

			// filters
			$args = apply_filters('acf/fields/relationship_multisite/query', $args, $field, $options['post_id']);
			$args = apply_filters('acf/fields/relationship_multisite/query/name=' . $field['name'], $args, $field, $options['post_id']);
			$args = apply_filters('acf/fields/relationship_multisite/query/key=' . $field['key'], $args, $field, $options['post_id']);

			// Get the blog id from the args array.
			$blog_id = $args['blog_id'] && (int) $args['blog_id'] > 0 ? (int) $args['blog_id'] : 0;
			// Remove the blog_id from the args array - so that it doesn't interfere with the query.
			unset($args['blog_id']);

			// If blog id is set, switch to that blog
			$blog_id && switch_to_blog($blog_id);

			// get posts grouped by post type
			$groups = acf_get_grouped_posts($args);

			// bail early if no posts
			if (empty($groups)) {
				// Restore the current blog, since we switched earlier.
				$blog_id &&	restore_current_blog();

				return false;
			}

			// loop
			foreach (array_keys($groups) as $group_title) {

				// vars
				$posts = acf_extract_var($groups, $group_title);

				// data
				$data = array(
					'text'     => $group_title,
					'children' => array(),
				);



				// convert post objects to post titles
				foreach (array_keys($posts) as $post_id) {

					$posts[$post_id] = $this->get_post_title($posts[$post_id], $field, $options['post_id']);
				}

				// order posts by search
				if ($is_search && empty($args['orderby']) && isset($args['s'])) {
					$posts = acf_order_by_search($posts, $args['s']);
				}

				// append to $data
				foreach (array_keys($posts) as $post_id) {
					$compound_id = $blog_id ? $post_id . ',' . $blog_id : $post_id;
					$data['children'][] = $this->get_post_result($compound_id, $posts[$post_id]);
				}

				// append to $results
				$results[] = $data;
			}

			// Restore the current blog, since we switched earlier.
			$blog_id &&	restore_current_blog();

			// add as optgroup or results
			if (count($args['post_type']) == 1) {
				$results = $results[0]['children'];
			}

			// vars
			$response = array(
				'results' => $results,
				'limit'   => $args['posts_per_page'],
			);

			// return
			return $response;
		}

		private function postAndBlogToId($post_id, $blog_id)
		{
			return $blog_id ? $post_id . ',' . $blog_id : $post_id;
		}

		private function idToPostAndBlog($id)
		{
			$parts = explode(',', $id);
			return array(
				'post_id' => $parts[0],
				'blog_id' => count($parts) > 1 ? $parts[1] : 0
			);
		}


		/**
		 * This function returns the HTML for a result
		 *
		 * @type    function
		 * @date    1/11/2013
		 * @since   5.0.0
		 *
		 * @param   $post (object)
		 * @param   $field (array)
		 * @param   $post_id (int) the post_id to which this value is saved to
		 * @return  (string)
		 */
		function get_post_title($post, $field, $post_id = 0, $is_search = 0)
		{

			// get post_id
			if (! $post_id) {
				$post_id = acf_get_form_data('post_id');
			}

			// vars
			$title = acf_get_post_title($post, $is_search);

			// featured_image
			if (acf_in_array('featured_image', $field['elements'])) {

				// vars
				$class     = 'thumbnail';
				$thumbnail = acf_get_post_thumbnail($post->ID, array(17, 17));

				// icon
				if ($thumbnail['type'] == 'icon') {
					$class .= ' -' . $thumbnail['type'];
				}

				// append
				$title = '<div class="' . $class . '">' . $thumbnail['html'] . '</div>' . $title;
			}

			// filters
			$title = apply_filters('acf/fields/relationship_multisite/result', $title, $post, $field, $post_id);
			$title = apply_filters('acf/fields/relationship_multisite/result/name=' . $field['_name'], $title, $post, $field, $post_id);
			$title = apply_filters('acf/fields/relationship_multisite/result/key=' . $field['key'], $title, $post, $field, $post_id);

			// return
			return $title;
		}


		/**
		 * Create the HTML interface for your field
		 *
		 * @param   $field - an array holding all the field's data
		 *
		 * @type    action
		 * @since   3.6
		 * @date    23/01/13
		 */
		function render_field($field)
		{

			// vars
			$post_type = acf_get_array($field['post_type']);
			$taxonomy  = acf_get_array($field['taxonomy']);
			$blog_id   = acf_get_array($field['blog_id']);
			$filters   = acf_get_array($field['filters']);

			// filters
			$filter_count             = count($filters);
			$filter_post_type_choices = array();
			$filter_taxonomy_choices  = array();
			$filter_blog_id_choices   = array();


			// post_type filter
			if (in_array('post_type', $filters)) {
				$filter_post_type_choices = array(
					'' => __('Select post type', 'acf'),
				) + acf_get_pretty_post_types($post_type);
			}


			// blog_id filter
			if (in_array('blog_id', $filters)) {
				// Get all blogs
				$pretty_blogs = $this->acf_get_pretty_subsites($blog_id);

				// Get this blog id
				$current_blog_id = get_current_blog_id();

				// Initialize the choices array
				$filter_blog_id_choices = array();

				// If the current blog is in the list
				if (isset($pretty_blogs[$current_blog_id])) {
					// Add the current blog to the top of the list
					$filter_blog_id_choices[$current_blog_id] = $pretty_blogs[$current_blog_id];

					// Remove the current blog from the list
					unset($pretty_blogs[$current_blog_id]);
				}

				// Add the rest of the blogs to the list
				$filter_blog_id_choices = $filter_blog_id_choices + $pretty_blogs;
			}

			// taxonomy filter
			if (in_array('taxonomy', $filters)) {
				$term_choices            = array();
				$filter_taxonomy_choices = array(
					'' => __('Select taxonomy', 'acf'),
				);

				// check for specific taxonomy setting
				if ($taxonomy) {
					$terms        = acf_get_encoded_terms($taxonomy);
					$term_choices = acf_get_choices_from_terms($terms, 'slug');

					// if no terms were specified, find all terms
				} else {

					// restrict taxonomies by the post_type selected
					$term_args = array();
					if ($post_type) {
						$term_args['taxonomy'] = acf_get_taxonomies(
							array(
								'post_type' => $post_type,
							)
						);
					}

					// get terms
					$terms        = acf_get_grouped_terms($term_args);
					$term_choices = acf_get_choices_from_grouped_terms($terms, 'slug');
				}

				// append term choices
				$filter_taxonomy_choices = $filter_taxonomy_choices + $term_choices;
			}

			// div attributes
			$atts = array(
				'id'             => $field['id'],
				// Keep the acf-relationship class for styling compatibility
				// Add the acf-relationship-multisite class for custom styling nd js targeting
				'class'          => "acf-relationship acf-relationship-multisite {$field['class']}",
				'data-min'       => $field['min'],
				'data-max'       => $field['max'],
				'data-s'         => '',
				'data-paged'     => 1,
				'data-post_type' => '',
				'data-taxonomy'  => '',
				'data-blog_id'   => '',
				'data-nonce'     => wp_create_nonce($field['key']),
			);

?>
			<div <?php echo acf_esc_attrs($atts); ?>>

				<?php
				acf_hidden_input(
					array(
						'name'  => $field['name'],
						'value' => '',
					)
				);
				?>

				<?php

				/* filters */
				if ($filter_count) :
				?>
					<div class="filters -f<?php echo esc_attr($filter_count); ?>">
						<?php

						/* search */
						if (in_array('search', $filters)) :
						?>
							<div class="filter -search">
								<?php
								acf_text_input(
									array(
										'placeholder' => __('Search...', 'acf'),
										'data-filter' => 's',
									)
								);
								?>
							</div>
						<?php
						endif;

						/* blog_id */
						if (in_array('blog_id', $filters)) :
						?>
							<div class="filter -blog_id">
								<?php
								acf_select_input(
									array(
										'choices'     => $filter_blog_id_choices,
										'data-filter' => 'blog_id',
										'value'       => array_keys($filter_blog_id_choices)[0]
									)
								);
								?>
							</div>
						<?php
						endif;

						/* post_type */
						if (in_array('post_type', $filters)) :
						?>
							<div class="filter -post_type">
								<?php
								acf_select_input(
									array(
										'choices'     => $filter_post_type_choices,
										'data-filter' => 'post_type',
									)
								);
								?>
							</div>
						<?php
						endif;

						/* post_type */
						if (in_array('taxonomy', $filters)) :
						?>
							<div class="filter -taxonomy">
								<?php
								acf_select_input(
									array(
										'choices'     => $filter_taxonomy_choices,
										'data-filter' => 'taxonomy',
									)
								);
								?>
							</div>
						<?php endif; ?>
					</div>
				<?php endif; ?>

				<div class="selection">
					<div class="choices">
						<ul class="acf-bl list choices-list"></ul>
					</div>
					<div class="values">
						<ul class="acf-bl list values-list">
							<?php
							if (! empty($field['value'])) :

								// loop
								foreach ($field['value'] as $compound_id) :
									// Get the post_id and blog_id from the compound id
									$ids = $this->idToPostAndBlog($compound_id);
									$post_title_suffix = '';

									// Is blog_id current blog? Then set it to 0
									if (absint($ids['blog_id']) === get_current_blog_id()) {
										$ids['blog_id'] = 0;
									}

									if ($ids['blog_id']) {
										switch_to_blog($ids['blog_id']);
										$post_title_suffix = ' (' . get_bloginfo('name') . ')';
									}

									// get post
									$post = get_post($ids['post_id']);

									// validate
									if (! $post) {
										error_log('no post');
										if ($ids['blog_id']) {
											restore_current_blog();
										}
										continue;
									}

							?>
									<li>
										<?php
										acf_hidden_input(
											array(
												'name'  => $field['name'] . '[]',
												'value' => $compound_id,
											)
										);
										?>
										<span tabindex="0" data-id="<?php echo $compound_id; ?>" class="acf-rel-item acf-rel-item-remove">
											<?php echo acf_esc_html($this->get_post_title($post, $field)) . $post_title_suffix; ?>
											<a href="#" class="acf-icon -minus small dark" data-name="remove_item"></a>
										</span>
									</li>
									<?php
									if ($ids['blog_id']) {
										restore_current_blog();
									}
									?>
								<?php endforeach; ?>
							<?php endif; ?>
						</ul>
					</div>
				</div>
			</div>
<?php
		}


		/**
		 * Create extra options for your field. This is rendered when editing a field.
		 * The value of $field['name'] can be used (like bellow) to save extra data to the $field
		 *
		 * @type    action
		 * @since   3.6
		 * @date    23/01/13
		 *
		 * @param   $field  - an array holding all the field's data
		 */
		function render_field_settings($field)
		{
			acf_render_field_setting(
				$field,
				array(
					'label'        => __('Filter by Post Type', 'acf'),
					'instructions' => '',
					'type'         => 'select',
					'name'         => 'post_type',
					'choices'      => acf_get_pretty_post_types(),
					'multiple'     => 1,
					'ui'           => 1,
					'allow_null'   => 1,
					'placeholder'  => __('All post types', 'acf'),
				)
			);

			acf_render_field_setting(
				$field,
				array(
					'label'        => __('Filter by Post Status', 'acf'),
					'instructions' => '',
					'type'         => 'select',
					'name'         => 'post_status',
					'choices'      => acf_get_pretty_post_statuses(),
					'multiple'     => 1,
					'ui'           => 1,
					'allow_null'   => 1,
					'placeholder'  => __('Any post status', 'acf'),
				)
			);

			acf_render_field_setting(
				$field,
				array(
					'label'        => __('Filter by Taxonomy', 'acf'),
					'instructions' => '',
					'type'         => 'select',
					'name'         => 'taxonomy',
					'choices'      => acf_get_taxonomy_terms(),
					'multiple'     => 1,
					'ui'           => 1,
					'allow_null'   => 1,
					'placeholder'  => __('All taxonomies', 'acf'),
				)
			);

			acf_render_field_setting(
				$field,
				array(
					'label'        => __('Filter by Subsite', 'acf'),
					'instructions' => '',
					'type'         => 'select',
					'name'         => 'blog_id',
					'choices'      => $this->acf_get_pretty_subsites(),
					'multiple'     => 1,
					'ui'           => 1,
					'allow_null'   => 1,
					'placeholder'  => __('All subsites', 'acf'),
				)
			);

			acf_render_field_setting(
				$field,
				array(
					'label'        => __('Filters', 'acf'),
					'instructions' => '',
					'type'         => 'checkbox',
					'name'         => 'filters',
					'choices'      => array(
						'search'    => __('Search', 'acf'),
						'post_type' => __('Post Type', 'acf'),
						'taxonomy'  => __('Taxonomy', 'acf'),
						'blog_id'  => __('Subsite', 'acf'),
					),
				)
			);

			acf_render_field_setting(
				$field,
				array(
					'label'        => __('Return Format', 'acf'),
					'instructions' => '',
					'type'         => 'radio',
					'name'         => 'return_format',
					'choices'      => array(
						'object' => __('Post Object', 'acf'),
						'id'     => __('Post ID and Blog ID', 'acf'),
					),
					'layout'       => 'horizontal',
				)
			);
		}


		/**
		 * This filter is applied to the $value after it is loaded from the db and before it is returned to the template
		 *
		 * @type    filter
		 * @since   3.6
		 * @date    23/01/13
		 *
		 * @param   $value (mixed) the value which was loaded from the database
		 * @param   $post_id (mixed) the post_id from which the value was loaded
		 * @param   $field (array) the field array holding all the field options
		 *
		 * @return  $value (mixed) the modified value
		 */
		function format_value($value, $post_id, $field)
		{
			// bail early if no value
			if (empty($value)) {
				return $value;
			}

			// force value to array
			$value = acf_get_array($value);

			$value = array_map(function ($v) {
				$ids = $this->idToPostAndBlog($v);
				$ids['post_id'] = intval($ids['post_id']);
				$ids['blog_id'] = intval($ids['blog_id']);
				return $ids;
			}, $value);

			// load posts if needed
			if ($field['return_format'] == 'object') {

				// get posts
				$value =  array_map(function ($v) use ($field) {
					if($v['blog_id'] === 0) {
						return get_post($v['post_id']);
					}
					switch_to_blog($v['blog_id']);
					$post = get_post($v['post_id']);
					// Check the post type
					if (!empty($field['post_type']) && !in_array($post->post_type, $field['post_type'])) {
						$post = null;
					}
					restore_current_blog();
					if($post) {
						$post->blog_id = $v['blog_id'];
					}
					return $post;
				}, $value);
			}

			// return
			return $value;
		}


		/**
		 * Filters the field value before it is saved into the database.
		 *
		 * @since 3.6
		 *
		 * @param mixed   $value   The value which will be saved in the database.
		 * @param integer $post_id The post_id of which the value will be saved.
		 * @param array   $field   The field array holding all the field options.
		 *
		 * @return mixed $value The modified value.
		 */
		public function update_value($value, $post_id, $field)
		{
			// Bail early if no value.
			if (empty($value)) {
				acf_update_bidirectional_values(array(), $post_id, $field);
				return $value;
			}

			// Format array of values.
			// - ensure each value is an id, or in the pattern blog_id:id.
			// - Parse each id as string for SQL LIKE queries.
			if (acf_is_sequential_array($value)) {

				$value = array_map(function ($v) {
					$ids = $this->idToPostAndBlog($v);
					$ids['post_id'] = acf_idval($ids['post_id']);
					$ids['post_id'] = strval($ids['post_id']);
					return $this->postAndBlogToId($ids['post_id'], $ids['blog_id']);
				}, $value);

				// Parse single value for id.
			} else {
				$ids = $this->idToPostAndBlog($value);
				$ids['post_id'] = acf_idval($ids['post_id']);
			}

			acf_update_bidirectional_values(acf_get_array($value), $post_id, $field);

			// Return value.
			return $value;
		}

		/**
		 * Return the schema array for the REST API.
		 *
		 * @param array $field
		 * @return array
		 */
		public function get_rest_schema(array $field)
		{
			$schema = array(
				'type'     => array('string', 'array', 'null'),
				'required' => ! empty($field['required']),
				'items'    => array(
					'type' => 'string',
				),
			);

			if (empty($field['allow_null'])) {
				$schema['minItems'] = 1;
			}

			if (! empty($field['min'])) {
				$schema['minItems'] = (int) $field['min'];
			}

			if (! empty($field['max'])) {
				$schema['maxItems'] = (int) $field['max'];
			}

			return $schema;
		}
	}

	// initialize
	acf_register_field_type('acf_field_relationship_multisite');

endif; // class_exists check


/**
 * JavaScript to register the field type
 *
 * Copy the way that ACF registers its field types in it's js file:
 * advanced-custom-fields-pro/assets/build/js/acf-input.js
 * 
 * But, instead of writing the field group from scratch, 
 * we can copy the existing relationship field and modify it.
 */
$acf_relationship_multisite_script = <<<JS
(function($, undefined) {
	var FieldCopy = acf.models["RelationshipField"].prototype;

	var RelationshipMultisiteField = acf.Field.extend({
		type: "relationship_multisite",
		events: FieldCopy.events,		
		\$control: function () {
			return this.$('.acf-relationship-multisite');
		},
		\$list: FieldCopy.\$list,
		\$listItems: FieldCopy.\$listItems,
		\$listItem: FieldCopy.\$listItem,
		getValue: FieldCopy.getValue,
		newChoice: FieldCopy.newChoice,
		newValue: FieldCopy.newValue,
		initialize: function () {
			// Get the initial filter value for blog_id
			var \$el = this.\$('.filter.-blog_id select');
			var val = \$el.val();
			var filter = \$el.data('filter');
			// update attr
			this.set(filter, val);

			// Run the original initialize function
			FieldCopy.initialize.call(this);
		},
		onScrollChoices: FieldCopy.onScrollChoices,
		onKeypressFilter: FieldCopy.onKeypressFilter,
		onChangeFilter: FieldCopy.onChangeFilter,
		onClickAdd: FieldCopy.onClickAdd,
		onClickRemove: FieldCopy.onClickRemove,
		onTouchStartValues: FieldCopy.onTouchStartValues,
		maybeFetch: FieldCopy.maybeFetch,
		getAjaxData: function () {
			// load data based on element attributes
			var ajaxData = this.\$control().data();
			for (var name in ajaxData) {
				ajaxData[name] = this.get(name);
			}

			// extra
			ajaxData.action = 'acf/fields/relationship_multisite/query';
			ajaxData.field_key = this.get('key');
			ajaxData.nonce = this.get('nonce');

			// Filter.
			ajaxData = acf.applyFilters('relationship_multisite_ajax_data', ajaxData, this);

			// return
			return ajaxData;
		},
		fetch: FieldCopy.fetch,
		walkChoices: FieldCopy.walkChoices,
	});

	acf.registerFieldType(RelationshipMultisiteField);
})(jQuery);
JS;

/**
 * Add inline script to the footer
 */
add_action(
	'acf/input/admin_print_footer_scripts',
	function () use ($acf_relationship_multisite_script) {
		echo "<script type='text/javascript'>{$acf_relationship_multisite_script}</script>";
	}
);


/**
 * CSS related to the field type
 *
 * 1. Centre the field type label - this element is shown in the modal when 'Browse Fields' is clicked.
 * 2. If there are 4 filters on the field, make the filter width 25%.
 */
$acf_relationship_multisite_styles = <<<CSS
.acf-field-type[data-field-type="relationship_multisite"] .field-type-label {
	text-align: center;
}
.acf-relationship-multisite .filters.-f4 .filter {
  width: 25%;
}
CSS;

/**
 * Add inline styles to the header
 */
add_action(
	'acf/input/admin_print_scripts',
	function () use ($acf_relationship_multisite_styles) {
		echo "<style type='text/css'>{$acf_relationship_multisite_styles}</style>";
	}
);

Thank you very much for the code! I added this to our site but unfortunately, no posts show up. The subsites to show up correctly in the dropdown field.

Im working with ACF 6.4.2 PRO and WordPress 6.8.1. The field is in a fieldgroup that is used in a block for Gutenberg. No eeror is showing up in the console. If you have any idea or known problems that would be great!

Edit: I got it working - apparently ACF made some changes in the latest versions but after comparing the code to the original and changing a few things it works!

Hi @naturfreunde-schweiz-organization-owner thanks for trying out the code. Sorry it's not working as you expect.

I have a few suggestions:

• Temporarily install ACF 6.3.6 and see if it works, if it does, then look for any changes in the ACF class acf_field_relationship that could cause the Gist to break.
• Add some breakpoints to the get_ajax_query function,
  • e.g. on line 236 error_log('calling acf_get_grouped_posts with args: ' . print_r($args, true) )
  • on line 244 add error_log('bailing early because no posts returned by acf_get_grouped_posts')

I don't use this code any more, or run multi-site for that matter, so apologies I won't be able to offer an update or fix beyond the vague suggestions.

Hope you get it working 🤞

Thank you very much! We got it working!

Brilliant! If you think you fix will help others, then please do share. And I'll update the Gist if necessary.

Good luck with the multi-site. ✌️ from Wales