Creating Relationships

The values of Pods fields only get saved when the post gets saved.

So for the values of one field to be filtered based on the values of another field, it requires a save and refresh.

For this reason, it’s not recommended to attempt this type of data structure with Pods.

The recommended approach would be a custom meta field with an AJAX call using JavaScript to allow the values for one field to change based on the value of another field.

Here is a plugin which, if installed for example to wp-content/plugins/make-model/make-model.php, will add a relational two-select box for managing a hierarchical taxonomy, make_model:

<?php
/**
 * Plugin Name: Make & Model
 * Description: Register a taxonomy <code>make_model</code> and add a meta box for managing it to post type <code>service_appointment</code>.
 * Version: 1
 * Author: 𝜑δ•ℂᴹ
 * Author URI: https://pd.cm/
 * Plugin URI: https://ww.wp.xz.cn/support/topic/creating-relationships/
 */


add_action(
	'init',
	function(){
		// https://developer.ww.wp.xz.cn/reference/functions/register_taxonomy/
		register_taxonomy(
			'make_model',
			[ 'service_appointment' ],
			[
				'show_ui'            => true,
			    'show_in_quick_edit' => true,
			    'meta_box_cb'        => false,
			    'hierarchical'       => true,
			    'labels'             => [
			    	'name'              => _x( 'Makes & Models', 'taxonomy general name', 'make_model' ),
					'singular_name'     => _x( 'Make & Model', 'taxonomy singular name', 'make_model' ),
					'search_items'      => __( 'Search Makes & Models', 'make_model' ),
					'all_items'         => __( 'All Makes & Models', 'make_model' ),
					'parent_item'       => __( 'Parent Make & Model', 'make_model' ),
					'parent_item_colon' => __( 'Parent Make & Model:', 'make_model' ),
					'edit_item'         => __( 'Edit Make & Model', 'make_model' ),
					'update_item'       => __( 'Update Make & Model', 'make_model' ),
					'add_new_item'      => __( 'Add New Make & Model', 'make_model' ),
					'new_item_name'     => __( 'New Make & Model Name', 'make_model' ),
					'menu_name'         => __( 'Make & Model', 'make_model' ),
			    ],
			]
		);
	}
);

add_action(
	'admin_init',
	function(){
		add_meta_box(
			'make_model',
			__( 'Make & Model', 'make_model' ),
			function(){
				// https://developer.ww.wp.xz.cn/reference/classes/wp_term_query/__construct/
				$terms = get_terms([
					'taxonomy'   => 'make_model',
					'orderby'    => 'parent',
					'hide_empty' => false,
					'fields'     => 'all',
				]);

				$selected_terms = wp_get_object_terms(
					get_the_ID(),
					'make_model',
					[
						'fields' => 'ids',
					]
				);

				$make_models = [];
				foreach( $terms as $term ) {
					if ( $term->parent === 0 ) {
						$make_models[ $term->term_id ]['name'] = $term->name;

						$make_models[ $term->term_id ]['selected'] = in_array( $term->term_id, $selected_terms );
					}else {
						$make_models[ $term->parent ]['models'][ $term->term_id ]['name'] = $term->name;
						$make_models[ $term->parent ]['models'][ $term->term_id ]['selected'] = in_array( $term->term_id, $selected_terms );
					}
				}
				?>
				<select id="make" name="make">
					<?php
						foreach( $make_models as $make_id => $make ) {
							printf(
								'<option value="%d" data-models="%s" %s>%s</option>',
								esc_attr( $make_id ),
								esc_attr( json_encode( $make['models'] ) ),
								selected( $make['selected'] ),
								esc_html( $make['name'] )
							);
						}
					?>
				</select>

				<select id="model" name="model"></select>

				<script>
					jQuery( document ).ready( function($){
						$('#make').on( 'change', function(){
							let models = JSON.parse( $(this).find('option:selected').attr( 'data-models' ) );

							$('#model').find('option').remove();

							$.each( models, function( term_id, model_obj ){
								let $option = $('<option>').val( term_id ).text( model_obj.name );

								if ( model_obj.selected ) {
									$option.attr( 'selected', 'selected' );
								}

								$('#model').append( $option );
							});
						});

						$('#make').trigger('change');
					});
				</script>
				<?php
			},
			[ 'service_appointment' ],
			'advanced',
			'high'
		);
	}
);

add_action(
	'save_post',
	function( $post_id ){
		if ( 'service_appointment' !== get_post_type( $post_id  ) ) {
			return;
		}

		if ( ! empty( $_POST['make'] ) && ! empty( $_POST['model'] ) ) {
			wp_set_object_terms(
				$post_id,
				[ (int) $_POST['make'], (int) $_POST['model'] ],
				'make_model',
				false
			);
		}
	}
);

The plugin causes the selection of “Make” to change the available options for “Model”, and causes the selection to override taxonomy term assignments for the post type. So the usual taxonomy term selection box is disabled and replaced with the dropdown, but other taxonomy user interface is still available:

Pods is still used for registering the custom post type, here is the Pods config for that:

{
"@meta": {
"version": "2.9.10.1",
"build": 1672143231
},
"pods": [
{
"name": "service_appointment",
"id": 10,
"label": "Service Appointments",
"description": "",
"type": "post_type",
"storage": "meta",
"label_singular": "Service Appointment",
"public": "1",
"show_ui": "1",
"rest_enable": "1",
"supports_title": "1",
"supports_editor": "1",
"_migrated_28": "1",
"required": "0",
"built_in_taxonomies_make": "1",
"built_in_taxonomies_model": "1",
"built_in_taxonomies_make_model": "1",
"groups": [
{
"name": "more_fields",
"id": 11,
"label": "More Fields",
"description": "",
"weight": 0,
"fields": []
}
]
}
]
}

register_post_type() could also be used, in which case Pods wouldn’t be necessary for the field to work.

• This reply was modified 3 years, 5 months ago by pdclark.