xml export of drafts was exporting everything

now only exports the drafts into the draft subdir
STUD-1627

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

@@ -679,7 +679,11 @@ class MongoModuleStore(ModuleStoreWriteBase):
                 and rules as kwargs below
             content (dict): fields to look for which have content scope. Follows same syntax and
                 rules as kwargs below.
-            revision (str): the revision of the items you're looking for.
+            revision (str): the revision of the items you're looking for. (only 'draft' makes sense for
+                this modulestore. If you don't provide a revision, it won't retrieve any drafts. If you
+                say 'draft', it will only return drafts. If you want one of each matching xblock but
+                preferring draft to published, call this same method on the draft modulestore w/o a
+                revision qualifier.)
             kwargs (key=value): what to look for within the course.
                 Common qualifiers are ``category`` or any field name. if the target field is a list,
                 then it searches for the given value in the list not list equivalence.

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

@@ -95,7 +95,7 @@ class DraftModuleStore(MongoModuleStore):
         draft_loc = as_draft(location)
         return super(DraftModuleStore, self).create_xmodule(draft_loc, definition_data, metadata, system, fields)
 
-    def get_items(self, course_key, settings=None, content=None, **kwargs):
+    def get_items(self, course_key, settings=None, content=None, revision=None, **kwargs):
         """
         Returns:
             list of XModuleDescriptor instances for the matching items within the course with
@@ -108,6 +108,9 @@ class DraftModuleStore(MongoModuleStore):
             course_key (CourseKey): the course identifier
             settings: not used
             content: not used
+            revision (str): the revision of the items you're looking for. Only 'draft' makes sense for
+                this modulestore. None implies get one of either the draft or published for each
+                matching xblock preferring the draft if it exists.
             kwargs (key=value): what to look for within the course.
                 Common qualifiers are ``category`` or any field name. if the target field is a list,
                 then it searches for the given value in the list not list equivalence.
@@ -118,6 +121,9 @@ class DraftModuleStore(MongoModuleStore):
             wrap_draft(item) for item in
             super(DraftModuleStore, self).get_items(course_key, revision='draft', **kwargs)
         ]
+        if revision == 'draft':
+            # the user only wants the drafts not everything w/ preference for draft
+            return draft_items
         draft_items_locations = {item.location for item in draft_items}
         non_draft_items = [
             item for item in

common/lib/xmodule/xmodule/modulestore/xml_exporter.py

@@ -126,7 +126,7 @@ def export_to_xml(modulestore, contentstore, course_key, root_dir, course_dir, d
     # should we change the application, then this assumption will no longer
     # be valid
     if draft_modulestore is not None:
-        draft_verticals = draft_modulestore.get_items(course_key, category='vertical')
+        draft_verticals = draft_modulestore.get_items(course_key, category='vertical', revision='draft')
         if len(draft_verticals) > 0:
             draft_course_dir = export_fs.makeopendir(DRAFT_DIR)
             for draft_vertical in draft_verticals: