Make categories endpoint return zero-value items (https://github.com/woocommerce/woocommerce-admin/pull/1755)

* Make categories endpoint return zero-value items

* Rename PHP variable to make it more specific

* Remove uneeded lines

* Remove second parameter from get_ids_table

plugins/woocommerce-admin/includes/data-stores/class-wc-admin-reports-categories-data-store.php

@@ -86,13 +86,15 @@ class WC_Admin_Reports_Categories_Data_Store extends WC_Admin_Reports_Data_Store
 		$sql_query_params['from_clause'] .= " LEFT JOIN {$wpdb->prefix}term_relationships ON {$order_product_lookup_table}.product_id = {$wpdb->prefix}term_relationships.object_id";
 		$sql_query_params['from_clause'] .= " LEFT JOIN {$wpdb->prefix}term_taxonomy ON {$wpdb->prefix}term_relationships.term_taxonomy_id = {$wpdb->prefix}term_taxonomy.term_taxonomy_id";
 
-		// Limit is left out here so that the grouping in code by PHP can be applied correctly.
-		// This also needs to be put after the term_taxonomy JOIN so that we can match the correct term name.
-		$sql_query_params = $this->get_order_by_params( $query_args, $sql_query_params );
-
 		$included_categories = $this->get_included_categories( $query_args );
 		if ( $included_categories ) {
 			$sql_query_params['where_clause'] .= " AND {$wpdb->prefix}term_taxonomy.term_id IN ({$included_categories})";
+
+			// Limit is left out here so that the grouping in code by PHP can be applied correctly.
+			// This also needs to be put after the term_taxonomy JOIN so that we can match the correct term name.
+			$sql_query_params = $this->get_order_by_params( $query_args, $sql_query_params, 'outer_from_clause', 'default_results.id' );
+		} else {
+			$sql_query_params = $this->get_order_by_params( $query_args, $sql_query_params, 'from_clause', "{$wpdb->prefix}term_taxonomy.term_id" );
 		}
 
 		// @todo Only products in the category C or orders with products from category C (and, possibly others?).
@@ -117,9 +119,11 @@ class WC_Admin_Reports_Categories_Data_Store extends WC_Admin_Reports_Data_Store
 	 *
 	 * @param array  $query_args Parameters supplied by the user.
 	 * @param array  $sql_query  Current SQL query array.
+	 * @param string $from_arg   Name of the FROM sql param.
+	 * @param string $id_cell    ID cell identifier, like `table_name.id_column_name`.
 	 * @return array
 	 */
-	protected function get_order_by_params( $query_args, $sql_query ) {
+	protected function get_order_by_params( $query_args, $sql_query, $from_arg, $id_cell ) {
 		global $wpdb;
 		$lookup_table = $wpdb->prefix . self::TABLE_NAME;
 
@@ -128,8 +132,9 @@ class WC_Admin_Reports_Categories_Data_Store extends WC_Admin_Reports_Data_Store
 			$sql_query['order_by_clause'] = $this->normalize_order_by( $query_args['orderby'] );
 		}
 
+		$sql_query['outer_from_clause'] = '';
 		if ( false !== strpos( $sql_query['order_by_clause'], '_terms' ) ) {
-			$sql_query['from_clause'] .= " JOIN {$wpdb->prefix}terms AS _terms ON {$wpdb->prefix}term_taxonomy.term_id = _terms.term_id";
+			$sql_query[ $from_arg ] .= " JOIN {$wpdb->prefix}terms AS _terms ON {$id_cell} = _terms.term_id";
 		}
 
 		if ( isset( $query_args['order'] ) ) {
@@ -157,6 +162,18 @@ class WC_Admin_Reports_Categories_Data_Store extends WC_Admin_Reports_Data_Store
 		return $order_by;
 	}
 
+	/**
+	 * Returns an array of ids of included categories, based on query arguments from the user.
+	 *
+	 * @param array $query_args Parameters supplied by the user.
+	 * @return string
+	 */
+	protected function get_included_categories_array( $query_args ) {
+		if ( isset( $query_args['categories'] ) && is_array( $query_args['categories'] ) && count( $query_args['categories'] ) > 0 ) {
+			return $query_args['categories'];
+		}
+		return array();
+	}
 
 	/**
 	 * Returns comma separated ids of included categories, based on query arguments from the user.
@@ -165,12 +182,8 @@ class WC_Admin_Reports_Categories_Data_Store extends WC_Admin_Reports_Data_Store
 	 * @return string
 	 */
 	protected function get_included_categories( $query_args ) {
-		$included_categories_str = '';
+		$included_categories = $this->get_included_categories_array( $query_args );
-
+		return implode( ',', $included_categories );
-		if ( isset( $query_args['categories'] ) && is_array( $query_args['categories'] ) && count( $query_args['categories'] ) > 0 ) {
-			$included_categories_str = implode( ',', $query_args['categories'] );
-		}
-		return $included_categories_str;
 	}
 
 	/**
@@ -241,9 +254,26 @@ class WC_Admin_Reports_Categories_Data_Store extends WC_Admin_Reports_Data_Store
 
 			$selections          = $this->selected_columns( $query_args );
 			$sql_query_params    = $this->get_sql_query_params( $query_args );
+			$included_categories = $this->get_included_categories_array( $query_args );
+
+			if ( count( $included_categories ) > 0 ) {
+				$fields          = $this->get_fields( $query_args );
+				$join_selections = $this->format_join_selections( array_merge( array( 'category_id' ), $fields ), 'category_id' );
+				$ids_table       = $this->get_ids_table( $included_categories );
+
+				$prefix     = "SELECT {$join_selections} FROM (";
+				$suffix     = ") AS {$table_name}";
+				$right_join = "RIGHT JOIN ( {$ids_table} ) AS default_results
+					ON default_results.id = {$table_name}.category_id";
+			} else {
+				$prefix     = '';
+				$suffix     = '';
+				$right_join = '';
+			}
 
 			$categories_data = $wpdb->get_results(
-				"SELECT
+				"${prefix}
+					SELECT
 						{$wpdb->prefix}term_taxonomy.term_id as category_id,
 						{$selections}
 					FROM
@@ -255,6 +285,9 @@ class WC_Admin_Reports_Categories_Data_Store extends WC_Admin_Reports_Data_Store
 						{$sql_query_params['where_clause']}
 					GROUP BY
 						category_id
+				{$suffix}
+					{$right_join}
+					{$sql_query_params['outer_from_clause']}
 					ORDER BY
 						{$sql_query_params['order_by_clause']}
 					",

plugins/woocommerce-admin/tests/api/reports-categories.php

@@ -84,6 +84,69 @@ class WC_Tests_API_Reports_Categories extends WC_REST_Unit_Test_Case {
 		$this->assertArrayHasKey( 'category', $category_report['_links'] );
 	}
 
+	/**
+	 * Test getting reports with the `categories` param.
+	 *
+	 * @since 3.5.0
+	 */
+	public function test_get_reports_categories_param() {
+		WC_Helper_Reports::reset_stats_dbs();
+		wp_set_current_user( $this->user );
+
+		// Populate all of the data.
+		$product = new WC_Product_Simple();
+		$product->set_name( 'Test Product' );
+		$product->set_regular_price( 25 );
+		$product->save();
+
+		$order = WC_Helper_Order::create_order( 1, $product );
+		$order->set_status( 'completed' );
+		$order->set_total( 100 ); // $25 x 4.
+		$order->save();
+
+		// Populate all of the data.
+		$product = new WC_Product_Simple();
+		$product->set_name( 'Test Product 2' );
+		$product->set_regular_price( 100 );
+		$second_category_id = wp_create_category( 'Second Category' );
+		$product->set_category_ids( array( $second_category_id ) );
+		$product->save();
+
+		WC_Helper_Queue::run_all_pending();
+
+		$uncategorized_term = get_term_by( 'slug', 'uncategorized', 'product_cat' );
+
+		$request = new WP_REST_Request( 'GET', $this->endpoint );
+		$request->set_query_params(
+			array(
+				'categories'   => $uncategorized_term->term_id . ',' . $second_category_id,
+			)
+		);
+		$response = $this->server->dispatch( $request );
+		$reports  = $response->get_data();
+
+		$this->assertEquals( 200, $response->get_status() );
+		$this->assertEquals( 2, count( $reports ) );
+
+		$category_report = reset( $reports );
+
+		$this->assertEquals( $second_category_id, $category_report['category_id'] );
+		$this->assertEquals( 0, $category_report['items_sold'] );
+		$this->assertEquals( 0, $category_report['orders_count'] );
+		$this->assertEquals( 0, $category_report['products_count'] );
+		$this->assertArrayHasKey( '_links', $category_report );
+		$this->assertArrayHasKey( 'category', $category_report['_links'] );
+
+		$category_report = next( $reports );
+
+		$this->assertEquals( $uncategorized_term->term_id, $category_report['category_id'] );
+		$this->assertEquals( 4, $category_report['items_sold'] );
+		$this->assertEquals( 1, $category_report['orders_count'] );
+		$this->assertEquals( 1, $category_report['products_count'] );
+		$this->assertArrayHasKey( '_links', $category_report );
+		$this->assertArrayHasKey( 'category', $category_report['_links'] );
+	}
+
 	/**
 	 * Test getting reports without valid permissions.
 	 *