diff --git a/CHANGELOG.md b/CHANGELOG.md
index d75510c..bdd3e60 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,12 @@
 # Yii2 Active Record Save Relations Behavior Change Log
 
+## [1.5.3] (unreleased)
+### Fixed
+- Bug #36: Fix an issue with HasMany relations with composite keys (thx @leandrogehlen)
+
+### Added
+- Enh #37: Add a `relationKeyName` property to determine the key used to load relations data.
+
 ## [1.5.2]
 ### Fixed
 - Fix a regression in Has One saving introduced by #30 fix.
@@ -17,7 +24,7 @@
 
 ## [1.5.0]
 ### Added
-- Enh #5: Ability to automaticaly delete related records along with the main model
+- Enh #5: Ability to automatically delete related records along with the main model
 
 ### Fixed
 - Bug #30: HasOne relation saving issue (thx @phrakon)
@@ -92,4 +99,4 @@
 - A new related model instance was previously generated instead.
 
 ## [1.0.0] 2016-03-26
-Initial release
\ No newline at end of file
+Initial release
diff --git a/README.md b/README.md
index 53c7d6a..c5462ef 100644
--- a/README.md
+++ b/README.md
@@ -277,3 +277,9 @@ $project->loadRelations(Yii::$app->request->post());
 
 You can even further simplify the process by adding the `SaveRelationsTrait` to your model.
 In that case, a call to the `load()` method will also automatically trigger a call to the `loadRelations()` method by using the same data, so you basically won't have to change your controllers.
+
+The `relationKeyName` property can be used to decide how the relations data will be retrieved from the data parameter. 
+
+Possible constants values are:
+* `SaveRelationsBehavior::RELATION_KEY_FORMNAME` (default): the key name will be compute using the model [`formName()`](https://www.yiiframework.com/doc/api/2.0/yii-base-model#formName()-detail) method
+* `SaveRelationsBehavior::RELATION_KEY_MODELNAME`: the relation name as defined in the behavior declarations will be used
diff --git a/src/SaveRelationsBehavior.php b/src/SaveRelationsBehavior.php
index 9e2b3bd..7748aa0 100644
--- a/src/SaveRelationsBehavior.php
+++ b/src/SaveRelationsBehavior.php
@@ -26,8 +26,11 @@ use yii\helpers\VarDumper;
 class SaveRelationsBehavior extends Behavior
 {
 
+    const RELATION_KEY_FORMNAME = 'formName';
+    const RELATION_KEY_MODELNAME = 'modelName';
+
     public $relations = [];
-    public $useFormName = true;
+    public $relationKeyName = self::RELATION_KEY_FORMNAME;
 
     private $_relations = [];
     private $_oldRelationValue = []; // Store initial relations value
@@ -732,12 +735,13 @@ class SaveRelationsBehavior extends Behavior
         /** @var BaseActiveRecord $owner */
         $owner = $this->owner;
         foreach ($this->_relations as $relationName) {
-            /** @var ActiveQuery $relation */
-            $relation = $owner->getRelation($relationName);
-            $modelClass = $relation->modelClass;
-            /** @var ActiveQuery $relationalModel */
-            $relationalModel = new $modelClass;
-            $keyName = $this->useFormName ? $relationalModel->formName() : $relationName;
+//            /** @var ActiveQuery $relation */
+//            $relation = $owner->getRelation($relationName);
+//            $modelClass = $relation->modelClass;
+//            /** @var ActiveQuery $relationalModel */
+//            $relationalModel = new $modelClass;
+            //$keyName = ($this->relationKeyName === self::RELATION_KEY_FORMNAME ? $relationalModel->formName() : $relationName);
+            $keyName = $this->_getRelationKeyName($relationName);
             if (array_key_exists($keyName, $data)) {
                 $owner->{$relationName} = $data[$keyName];
             }
@@ -762,4 +766,31 @@ class SaveRelationsBehavior extends Behavior
         }
 
     }
+
+    /**
+     * @param $relationName
+     * @return mixed
+     * @throws InvalidConfigException
+     */
+    private function _getRelationKeyName($relationName)
+    {
+        switch ($this->relationKeyName) {
+            case self::RELATION_KEY_MODELNAME:
+                $keyName = $relationName;
+                break;
+            case self::RELATION_KEY_FORMNAME:
+                /** @var BaseActiveRecord $owner */
+                $owner = $this->owner;
+                /** @var ActiveQuery $relation */
+                $relation = $owner->getRelation($relationName);
+                $modelClass = $relation->modelClass;
+                /** @var ActiveQuery $relationalModel */
+                $relationalModel = new $modelClass;
+                $keyName = $relationalModel->formName();
+                break;
+            default:
+                throw new InvalidConfigException('Unknown relation key name');
+        }
+        return $keyName;
+    }
 }
diff --git a/tests/SaveRelationsBehaviorTest.php b/tests/SaveRelationsBehaviorTest.php
index d830d9c..099e5f7 100644
--- a/tests/SaveRelationsBehaviorTest.php
+++ b/tests/SaveRelationsBehaviorTest.php
@@ -850,9 +850,9 @@ class SaveRelationsBehaviorTest extends \PHPUnit_Framework_TestCase
         ]);
 
         $company->attachBehavior('saveRelations', [
-            'class' => SaveRelationsBehavior::className(),
-            'relations' => ['users'],
-            'useFormName' => false
+            'class'           => SaveRelationsBehavior::className(),
+            'relations'       => ['users'],
+            'relationKeyName' => SaveRelationsBehavior::RELATION_KEY_MODELNAME
         ]);
 
         $data = [