REST API: Add support for modifying the term relation when querying posts.

By default, a post most contain any of the requested terms to be included in the response. This commit adds a new `operator` property that can be set to `AND` to require a post to contain all of the requested terms.

For example, `/wp/v2/posts?tags[terms]=1,2,3&tags[operator]=AND` will return posts that have tags with the ids of 1, 2, and 3.

Props dlh, earnjam, Clorith, jnylen0, sebbb.
Fixes #41287.


git-svn-id: https://develop.svn.wordpress.org/trunk@51026 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/rest-api/endpoints/class-wp-rest-posts-controller.php

@@ -2941,12 +2941,17 @@ class WP_REST_Posts_Controller extends WP_REST_Controller {
 			if ( $tax_include ) {
 				$terms            = array();
 				$include_children = false;
+				$operator         = 'IN';
 
 				if ( rest_is_array( $tax_include ) ) {
 					$terms = $tax_include;
 				} elseif ( rest_is_object( $tax_include ) ) {
 					$terms            = empty( $tax_include['terms'] ) ? array() : $tax_include['terms'];
 					$include_children = ! empty( $tax_include['include_children'] );
+
+					if ( isset( $tax_include['operator'] ) && 'AND' === $tax_include['operator'] ) {
+						$operator = 'AND';
+					}
 				}
 
 				if ( $terms ) {
@@ -2955,6 +2960,7 @@ class WP_REST_Posts_Controller extends WP_REST_Controller {
 						'field'            => 'term_id',
 						'terms'            => $terms,
 						'include_children' => $include_children,
+						'operator'         => $operator,
 					);
 				}
 			}
@@ -3048,6 +3054,14 @@ class WP_REST_Posts_Controller extends WP_REST_Controller {
 			),
 			$limit_schema
 		);
+		// 'operator' is supported only for 'include' queries.
+		$include_schema['oneOf'][1]['properties']['operator'] = array(
+			'description' => __( 'Whether items must be assigned all or any of the specified terms.' ),
+			'type'        => 'string',
+			'enum'        => array( 'AND', 'OR' ),
+			'default'     => 'OR',
+		);
+
 		$exclude_schema = array_merge(
 			array(
 				/* translators: %s: Taxonomy name. */

tests/phpunit/tests/rest-api/rest-posts-controller.php

@@ -1294,6 +1294,47 @@ class WP_Test_REST_Posts_Controller extends WP_Test_REST_Post_Type_Controller_Te
 		$this->assertContains( $p2, $found_ids );
 	}
 
+	/**
+	 * @ticket 41287
+	 */
+	public function test_get_items_with_all_categories() {
+		$taxonomy   = get_taxonomy( 'category' );
+		$categories = static::factory()->term->create_many( 2, array( 'taxonomy' => $taxonomy->name ) );
+
+		$p1 = static::factory()->post->create(
+			array(
+				'post_status'   => 'publish',
+				'post_category' => array( $categories[0] ),
+			)
+		);
+		$p2 = static::factory()->post->create(
+			array(
+				'post_status'   => 'publish',
+				'post_category' => array( $categories[1] ),
+			)
+		);
+		$p3 = static::factory()->post->create(
+			array(
+				'post_status'   => 'publish',
+				'post_category' => $categories,
+			)
+		);
+
+		$request = new WP_REST_Request( 'GET', '/wp/v2/posts' );
+		$request->set_param(
+			$taxonomy->rest_base,
+			array(
+				'terms'    => $categories,
+				'operator' => 'AND',
+			)
+		);
+		$response = rest_get_server()->dispatch( $request );
+		$data     = $response->get_data();
+
+		$this->assertCount( 1, $data );
+		$this->assertSame( $p3, $data[0]['id'] );
+	}
+
 	/**
 	 * @ticket 44326
 	 */