Some changes to make hasMAny eager loading work after making

primaryKey() return array

Cake/ORM/Association/ExternalAssociationTrait.php

@@ -147,13 +147,16 @@ protected function _joinCondition(array $options) {
  */
 	protected function _resultInjector($fetchQuery, $resultMap) {
 		$source = $this->source();
-		$sourceKey = key($fetchQuery->aliasField(
-			$source->primaryKey(),
-			$source->alias()
-		));
+		$sAlias = $source->alias();
+		$tAlias = $this->target()->alias();
+
+		$sourceKeys = [];
+		foreach ($source->primaryKey() as $key) {
+			$sourceKeys[] = key($fetchQuery->aliasField($key, $sAlias));
+		}
 
-		$alias = $this->target()->alias();
-		$nestKey = $alias . '__' . $alias;
+		$sourceKey = implode(';', $sourceKeys);
+		$nestKey = $tAlias . '__' . $tAlias;
 		return function($row) use ($resultMap, $sourceKey, $nestKey) {
 			if (isset($resultMap[$row[$sourceKey]])) {
 				$row[$nestKey] = $resultMap[$row[$sourceKey]];

Cake/ORM/Query.php

@@ -1041,18 +1041,31 @@ protected function _collectKeys($statement) {
 			$source = $meta['instance']->source();
 			if ($meta['instance']->requiresKeys($meta['config'])) {
 				$alias = $source->alias();
-				$pkField = key($this->aliasField($source->primaryKey(), $alias));
-				$collectKeys[] = [$alias, $pkField];
+				$pkFields = [];
+				foreach($source->primaryKey() as $key) {
+					$pkFields[] = key($this->aliasField($key, $alias));
+				}
+				$collectKeys[] = [$alias, $pkFields, count($pkFields) === 1];
 			}
 		}
 
 		$keys = [];
 		if (!empty($collectKeys)) {
 			while ($result = $statement->fetch('assoc')) {
 				foreach ($collectKeys as $parts) {
-					$keys[$parts[0]][] = $result[$parts[1]];
+					if ($parts[2]) {
+						$keys[$parts[0]][] = $result[$parts[1][0]];
+						continue;
+					}
+
+					$collected = [];
+					foreach ($parts[1] as $key) {
+						$collected[] = $result[$key];
+					}
+					$keys[$parts[0]][] = $collected;
 				}
 			}
+
 			$statement->rewind();
 		}