Fix BelongsToMany saving incorrectly when _joinData is used.

When the `_joinData` has not been fully marshalled, BelongsToMany
associations will not save the joinData correctly. This can cause data
to go 'missing' when associations with conditions are involved.

Refs #7808

src/ORM/Association/BelongsToMany.php

@@ -622,11 +622,13 @@ protected function _saveLinks(EntityInterface $sourceEntity, $targetEntities, $o
         $junctionAlias = $junction->alias();
 
         foreach ($targetEntities as $e) {
-            $joint = $e->get($jointProperty);
+            $joint = $jointVal = $e->get($jointProperty);
             if (!$joint || !($joint instanceof EntityInterface)) {
                 $joint = new $entityClass([], ['markNew' => true, 'source' => $junctionAlias]);
+                if (is_array($jointVal)) {
+                    $joint->set($jointVal);
+                }
             }
-
             $sourceKeys = array_combine($foreignKey, $sourceEntity->extract($bindingKey));
             $targetKeys = array_combine($assocForeignKey, $e->extract($targetPrimaryKey));
 

tests/TestCase/ORM/Association/BelongsToManyTest.php

@@ -656,6 +656,38 @@ public function testReplaceLinkWithConditions()
         $this->assertSame(1, $jointCount, 'Non matching joint record should remain.');
     }
 
+    /**
+     * Tests that replaceLinks will apply _joinData when it has not been converted
+     * to an entity if that data is an array.
+     *
+     * @return void
+     */
+    public function testReplaceLinkJoinDataHandling()
+    {
+        $joint = TableRegistry::get('SpecialTags');
+        $articles = TableRegistry::get('Articles');
+
+        $assoc = $articles->belongsToMany('Tags', [
+            'through' => 'SpecialTags',
+            'conditions' => ['SpecialTags.highlighted' => true]
+        ]);
+        $id = 2;
+        $entity = $articles->get($id, ['contain' => 'Tags']);
+
+        // New tag
+        $tagData = [
+            new Entity(['id' => 2, '_joinData' => ['highlighted' => true]]),
+        ];
+
+        $assoc->replaceLinks($entity, $tagData);
+        $this->assertSame($tagData, $entity->tags, 'Tags should match replaced objects');
+        $this->assertFalse($entity->dirty('tags'), 'Should be clean');
+
+        $jointRecords = $joint->find()->where(['article_id' => $id])->toArray();
+        $this->assertCount(1, $jointRecords);
+        $this->assertTrue($jointRecords[0]->highlighted, 'joinData should be set.');
+    }
+
     /**
      * Provider for empty values
      *