Implement copy_all_asset_metadata for Old Mongo->Old Mongo.

Add tests for copying all asset metadata.
https://openedx.atlassian.net/browse/PLAT-74

common/lib/xmodule/xmodule/assetstore/__init__.py

@@ -106,7 +106,7 @@ class AssetMetadata(object):
             'edited_on': self.edited_on
         }
 
-    @contract(asset_doc='dict | None')
+    @contract(asset_doc='dict|None')
     def from_mongo(self, asset_doc):
         """
         Fill in all metadata fields from a MongoDB document.
@@ -134,7 +134,7 @@ class AssetThumbnailMetadata(object):
     # All AssetThumbnailMetadata objects should have AssetLocators with this type.
     ASSET_TYPE = 'thumbnail'
 
-    @contract(asset_id='AssetKey', internal_name='str | unicode | None')
+    @contract(asset_id='AssetKey', internal_name='basestring|None')
     def __init__(self, asset_id, internal_name=None, field_decorator=None):
         """
         Construct a AssetThumbnailMetadata object.
@@ -160,7 +160,7 @@ class AssetThumbnailMetadata(object):
             'internal_name': self.internal_name
         }
 
-    @contract(thumbnail_doc='dict | None')
+    @contract(thumbnail_doc='dict|None')
     def from_mongo(self, thumbnail_doc):
         """
         Fill in all metadata fields from a MongoDB document.

common/lib/xmodule/xmodule/modulestore/__init__.py

@@ -392,7 +392,7 @@ class ModuleStoreAssetInterface(object):
         sort_field = 'filename'
         sort_order = 'ascending'
         if sort:
-            if sort[0] == 'uploadDate':
+            if sort[0] == 'uploadDate' and not get_thumbnails:
                 sort_field = 'edited_on'
             if sort[1] == 'descending':
                 sort_order = 'descending'

common/lib/xmodule/xmodule/modulestore/mongo/base.py

@@ -1518,6 +1518,28 @@ class MongoModuleStore(ModuleStoreDraftAndPublished, ModuleStoreWriteBase, Mongo
         self.asset_collection.update({'_id': course_assets['_id']}, {'$set': {info: all_assets.as_list()}})
         return True
 
+    @contract(source_course_key='CourseKey', dest_course_key='CourseKey')
+    def copy_all_asset_metadata(self, source_course_key, dest_course_key, user_id):
+        """
+        Copy all the course assets from source_course_key to dest_course_key.
+
+        Arguments:
+            source_course_key (CourseKey): identifier of course to copy from
+            dest_course_key (CourseKey): identifier of course to copy to
+        """
+        source_assets = self._find_course_assets(source_course_key)
+        dest_assets = self._find_course_assets(dest_course_key)
+        dest_assets['assets'] = source_assets.get('assets', [])
+        dest_assets['thumbnails'] = source_assets.get('thumbnails', [])
+
+        # Update the document.
+        self.asset_collection.update(
+            {'_id': dest_assets['_id']},
+            {'$set': {'assets': dest_assets['assets'],
+                      'thumbnails': dest_assets['thumbnails']}
+             }
+        )
+
     @contract(asset_key='AssetKey', attr_dict=dict)
     def set_asset_metadata_attrs(self, asset_key, attr_dict, user_id):
         """