Switch get repo API to use a single list tags query

Should make things faster since the join occurs on the database side

data/model/tag.py

@@ -83,13 +83,30 @@ def filter_tags_have_repository_event(query, event):
           .order_by(RepositoryTag.lifetime_start_ts.desc()))
 
 
-def get_tag_manifests(tags):
-  """ Returns a map from tag ID to its associated manifest, if any. """
+def get_tag_manifest_digests(tags):
+  """ Returns a map from tag ID to its associated manifest digest, if any. """
   if not tags:
     return dict()
 
-  manifests = TagManifest.select().where(TagManifest.tag << [t.id for t in tags])
-  return {manifest.tag_id:manifest for manifest in manifests}
+  manifests = (TagManifest
+               .select(TagManifest.tag, TagManifest.digest)
+               .where(TagManifest.tag << [t.id for t in tags]))
+
+  return {manifest.tag_id: manifest.digest for manifest in manifests}
+
+
+def list_active_repo_tags(repo):
+  """ Returns all of the active, non-hidden tags in a repository, joined to they images
+      and (if present), their manifest.
+  """
+  query = _tag_alive(RepositoryTag
+                     .select(RepositoryTag, Image, TagManifest.digest)
+                     .join(Image)
+                     .where(RepositoryTag.repository == repo)
+                     .switch(RepositoryTag)
+                     .join(TagManifest, JOIN_LEFT_OUTER))
+
+  return query
 
 
 def list_repository_tags(namespace_name, repository_name, include_hidden=False,
@@ -320,7 +337,7 @@ def list_repository_tag_history(repo_obj, page=1, size=100, specific_tag=None):
   if not tags:
     return [], {}, False
 
-  manifest_map = get_tag_manifests(tags)
+  manifest_map = get_tag_manifest_digests(tags)
   return tags[0:size], manifest_map, len(tags) > size