Persist changed metadata in git

When only the metadata of an entry got changed, gdatastore only
updated the Xapian index but neglected git. This caused the change not
to persist across an index rebuild and not to propagate across
gdatastore instances.

We now store the updated metadata in a new commit with the same ref
name and having the previous ref as parent. This should be enough for
the index rebuild case. It will also propagate nicely through git,
though we don't have code in place yet to notice updated entries
(rather than completely new ones).

1 files changed, 14 insertions, 0 deletions

diff --git a/gdatastore/datastore.py b/gdatastore/datastore.py
index 6dd2170..a33aca8 100644
--- a/gdatastore/datastore.py
+++ b/gdatastore/datastore.py
@@ -542,6 +542,7 @@ class InternalApi(object):
             old_metadata = self._index.retrieve(object_id)['metadata']
             metadata['creation_time'] = old_metadata['creation_time']
 
+        self._update_metadata_in_git(object_id, metadata)
         self._index.store(object_id, metadata)
         self._invoke_callbacks('change_metadata', object_id, metadata)
 
@@ -815,6 +816,19 @@ class InternalApi(object):
         finally:
             shutil.rmtree(index_dir)
 
+    def _update_metadata_in_git(self, object_id, metadata):
+        commit_message = self._format_commit_message(metadata)
+        tree_hash = self._get_tree_hash(object_id)
+        ref = _format_ref(*object_id)
+        commit_hash = self._git_call('commit-tree', ['-p', ref, tree_hash],
+                                     input=commit_message).strip()
+        self._git_call('update-ref', [ref, commit_hash])
+
+    def _get_tree_hash(self, object_id):
+        args = ['commit', _format_ref(*object_id)]
+        # First line of output contains tree hash
+        return self._git_call('cat-file', args).split('\n', 1)[0].split(' ')[1]
+
     def _get_object_ids_from_git(self):
         args = ['--sort=committerdate', '--format=%(refname)',
                 'refs/gdatastore/*/*']