Adding unit test for EntityContext extracting _ids

src/View/Form/EntityContext.php

@@ -210,12 +210,20 @@ public function val($field) {
 		return null;
 	}
 
+/**
+ * Helper method used to extract all the primary key values out of an array, The
+ * primary key column is guessed out of the provided $path array
+ *
+ * @param array|\Traversable $values The list from wich to extract primary keys from
+ * @param array $path Each one of the parts in a path for a field name
+ * @return array
+ */
 	protected function _extractMultiple($values, $path) {
 		if (!(is_array($values) || $values instanceof \Traversable)) {
 			return null;
 		}
-		$table = $this->_getTable($path);
-		$primary = (array)$table->primaryKey();
+		$table = $this->_getTable($path, false);
+		$primary = $table ? (array)$table->primaryKey() : ['id'];
 		return (new Collection($values))->extract($primary[0])->toArray();
 	}
 
@@ -336,7 +344,7 @@ protected function _getValidator($parts) {
  * @return array containing the table instance in the first position and the
  * property name in the second position
  */
-	protected function _getTable($parts) {
+	protected function _getTable($parts, $rootFallback = true) {
 		if (count($parts) === 1) {
 			return $this->_tables[$this->_rootName];
 		}
@@ -357,9 +365,12 @@ protected function _getTable($parts) {
 		$table = $this->_tables[$this->_rootName];
 		foreach ($normalized as $part) {
 			$assoc = $table->associations()->getByProperty($part);
-			if (!$assoc) {
+			if (!$assoc && $rootFallback) {
 				break;
 			}
+			if (!$assoc && !$rootFallback) {
+				return false;
+			}
 
 			$table = $assoc->target();
 		}

tests/TestCase/View/Form/EntityContextTest.php

@@ -444,6 +444,32 @@ public function testValAssociatedHasMany() {
 		$this->assertEquals('Second post', $result);
 	}
 
+/**
+ * Test reading values for magic _ids input
+ *
+ * @return void
+ */
+	public function testValAssociatedIds() {
+		$row = new Entity([
+			'title' => 'First post',
+			'user' => new Entity([
+				'username' => 'mark',
+				'fname' => 'Mark',
+				'groups' => [
+					new Entity(['title' => 'PHP', 'id' => 1]),
+					new Entity(['title' => 'Javascript', 'id' => 2]),
+				]
+			]),
+		]);
+		$context = new EntityContext($this->request, [
+			'entity' => $row,
+			'table' => 'Articles',
+		]);
+
+		$result = $context->val('user.groups._ids');
+		$this->assertEquals([1, 2], $result);
+	}
+
 /**
  * Test validator as a string.
  *