diff --git a/lib/Doctrine/ORM/UnitOfWork.php b/lib/Doctrine/ORM/UnitOfWork.php
index 8f82aa96f..0294b9f82 100644
--- a/lib/Doctrine/ORM/UnitOfWork.php
+++ b/lib/Doctrine/ORM/UnitOfWork.php
@@ -49,6 +49,7 @@ use Doctrine\ORM\Persisters\Entity\JoinedSubclassPersister;
 use Doctrine\ORM\Persisters\Collection\OneToManyPersister;
 use Doctrine\ORM\Persisters\Collection\ManyToManyPersister;
 use Doctrine\ORM\Utility\IdentifierFlattener;
+use Doctrine\ORM\Cache\AssociationCacheEntry;
 
 /**
  * The UnitOfWork is responsible for tracking changes to objects during an
@@ -2490,22 +2491,7 @@ class UnitOfWork implements PropertyChangedListener
         $class = $this->em->getClassMetadata($className);
         //$isReadOnly = isset($hints[Query::HINT_READ_ONLY]);
 
-        if ($class->isIdentifierComposite) {
-            $id = array();
-
-            foreach ($class->identifier as $fieldName) {
-                $id[$fieldName] = isset($class->associationMappings[$fieldName])
-                    ? $data[$class->associationMappings[$fieldName]['joinColumns'][0]['name']]
-                    : $data[$fieldName];
-            }
-        } else {
-            $id = isset($class->associationMappings[$class->identifier[0]])
-                ? $data[$class->associationMappings[$class->identifier[0]]['joinColumns'][0]['name']]
-                : $data[$class->identifier[0]];
-
-            $id = array($class->identifier[0] => $id);
-        }
-
+        $id = $this->identifierFlattener->flattenIdentifier($class, $data);
         $idHash = implode(' ', $id);
 
         if (isset($this->identityMap[$class->rootEntityName][$idHash])) {
@@ -2639,10 +2625,18 @@ class UnitOfWork implements PropertyChangedListener
 
                         if ($joinColumnValue !== null) {
                             if ($targetClass->containsForeignIdentifier) {
+                                if ($joinColumnValue instanceof AssociationCacheEntry) {
+                                    $joinColumnValue = implode(' ', $joinColumnValue->identifier);
+                                }
+
                                 $associatedId[$targetClass->getFieldForColumn($targetColumn)] = $joinColumnValue;
                             } else {
                                 $associatedId[$targetClass->fieldNames[$targetColumn]] = $joinColumnValue;
                             }
+                        } elseif ($targetClass->containsForeignIdentifier && in_array($targetClass->getFieldForColumn($targetColumn), $targetClass->identifier, true)) {
+                            // the missing key is part of target's entity primary key
+                            $associatedId = array();
+                            break;
                         }
                     }
 
diff --git a/lib/Doctrine/ORM/Utility/IdentifierFlattener.php b/lib/Doctrine/ORM/Utility/IdentifierFlattener.php
index 166e0acb6..fbad711e3 100644
--- a/lib/Doctrine/ORM/Utility/IdentifierFlattener.php
+++ b/lib/Doctrine/ORM/Utility/IdentifierFlattener.php
@@ -71,22 +71,24 @@ final class IdentifierFlattener
     {
         $flatId = array();
 
-        foreach ($id as $idField => $idValue) {
-            if (isset($class->associationMappings[$idField]) && is_object($idValue)) {
-                /* @var $targetClassMetadata ClassMetadata */
+       foreach ($class->identifier as $field) {
+            if (isset($class->associationMappings[$field]) && isset($id[$field]) && is_object($id[$field])) {
                 $targetClassMetadata = $this->metadataFactory->getMetadataFor(
-                    $class->associationMappings[$idField]['targetEntity']
+                    $class->associationMappings[$field]['targetEntity']
                 );
-
-                $associatedId = $this->unitOfWork->isInIdentityMap($idValue)
-                    ? $this->unitOfWork->getEntityIdentifier($idValue)
-                    : $targetClassMetadata->getIdentifierValues($idValue);
-
-                $flatId[$idField] = $associatedId[$targetClassMetadata->identifier[0]];
+                $associatedId = $this->flattenIdentifier($targetClassMetadata, $this->unitOfWork->getEntityIdentifier($id[$field]));
+                $flatId[$field] = implode(' ', $associatedId);
+            } elseif (isset($class->associationMappings[$field])) {
+                $associatedId = array();
+                foreach ($class->associationMappings[$field]['joinColumns'] as $joinColumn) {
+                    $associatedId[] = $id[$joinColumn['name']];
+                }
+                $flatId[$field] = implode(' ', $associatedId);
             } else {
-                $flatId[$idField] = $idValue;
+                $flatId[$field] = $id[$field];
             }
         }
+        
 
         return $flatId;
     }
diff --git a/tests/Doctrine/Tests/ORM/Utility/IdentifierFlattenerTest.php b/tests/Doctrine/Tests/ORM/Utility/IdentifierFlattenerTest.php
index 63536c886..dad6ce4b3 100644
--- a/tests/Doctrine/Tests/ORM/Utility/IdentifierFlattenerTest.php
+++ b/tests/Doctrine/Tests/ORM/Utility/IdentifierFlattenerTest.php
@@ -9,6 +9,7 @@ use Doctrine\Tests\Models\Cache\City;
 use Doctrine\Tests\Models\Cache\Flight;
 use Doctrine\ORM\ORMException;
 use Doctrine\ORM\Utility\IdentifierFlattener;
+
 /**
  * Test the IdentifierFlattener utility class
  *
@@ -87,7 +88,7 @@ class IdentifierFlattenerTest extends OrmFunctionalTestCase
 
         $this->assertArrayHasKey('secondEntity', $flatIds, 'It should be called secondEntity');
 
-        $this->assertSame($id['secondEntity']->id, $flatIds['secondEntity']);
+        $this->assertEquals($id['secondEntity']->id, $flatIds['secondEntity']);
     }
 
     /**
@@ -115,8 +116,8 @@ class IdentifierFlattenerTest extends OrmFunctionalTestCase
         $this->assertArrayHasKey('leavingFrom', $id);
         $this->assertArrayHasKey('goingTo', $id);
 
-        $this->assertSame($leeds, $id['leavingFrom']);
-        $this->assertSame($london, $id['goingTo']);
+        $this->assertEquals($leeds, $id['leavingFrom']);
+        $this->assertEquals($london, $id['goingTo']);
 
         $flatIds = $this->identifierFlattener->flattenIdentifier($class, $id);
 
@@ -125,7 +126,7 @@ class IdentifierFlattenerTest extends OrmFunctionalTestCase
         $this->assertArrayHasKey('leavingFrom', $flatIds);
         $this->assertArrayHasKey('goingTo', $flatIds);
 
-        $this->assertSame($id['leavingFrom']->getId(), $flatIds['leavingFrom']);
-        $this->assertSame($id['goingTo']->getId(), $flatIds['goingTo']);
+        $this->assertEquals($id['leavingFrom']->getId(), $flatIds['leavingFrom']);
+        $this->assertEquals($id['goingTo']->getId(), $flatIds['goingTo']);
     }
 }