Add an index for db.charms.

charmworld/migrations/migrate.py

Index: charmworld/migrations/migrate.py
=== modified file 'charmworld/migrations/migrate.py'
--- charmworld/migrations/migrate.py	2013-12-19 19:45:36 +0000
+++ charmworld/migrations/migrate.py	2014-02-11 14:43:04 +0000
@@ -1,10 +1,24 @@
-# Copyright 2012, 2013 Canonical Ltd.  This software is licensed under the
+# Copyright 2012-2014 Canonical Ltd.  This software is licensed under the
 # GNU Affero General Public License version 3 (see the file LICENSE).
 
 """Migrate data for the mongodb instance.
 
 Loads migrations from the latest available in the versions directory.
 
+The versioning can take the form of migrations and exoduses.  A migration is a
+simple data transformation that is expected to apply to a populated database
+in a short amount of time.  Generally five minutes is the maximum amount of
+time allowed for all migrations for a given version.  Migrations transform the
+data in place and may block other operations on the collection.
+
+If a transformation is expected to take longer, it should be written as an
+exodus.  An exodus makes a temporary copy of the charm collection, applies the
+transformation, and then replaces the original copy with the new version.
+Other operations on the charm collection are not blocked with the exodus
+runs.
+
+For any given upgrade, there may be at most one exodus and it must be run
+before any subsequent migrations.
 """
 import argparse
 from collections import namedtuple
@@ -16,6 +30,7 @@
 from os.path import join
 import re
 
+import pymongo
 from pymongo.errors import OperationFailure
 
 from charmworld.models import (
@@ -29,20 +44,31 @@
 from charmworld.utils import configure_logging
 
 
-SCRIPT_TEMPLATE = """
+SCRIPT_TEMPLATE = '''\
 # {description}
 
+
 def upgrade(db, index_client):
-    \"\"\"Complete this function with work to be done for the migration/update.
+    """Complete this function with work to be done for the migration/update.
 
     db is the pymongo db instance for our datastore. Charms are in db.charms
     for instance.
 
     index_client is the ElasticSearch client.
-    \"\"\"
-
-
-"""
+    """
+    pass
+
+
+## def exodus_update(source, target, current_version):
+##     """Complete this function with work for an exodus.
+
+##     source is the original CharmSource.
+##     target is the CharmSource to be used after the exodus.
+##     current_version is the version of this exodus.
+##     """
+##     pass
+
+'''
 
 
 def str_to_filename(s):
@@ -56,6 +82,36 @@
     return s
 
 
+def setup_qa_data(db):
+    """Setup the QA questions."""
+    for category_dict in iter_categories():
+        db.qa.insert(category_dict)
+
+
+def setup_mongo_indices(charms):
+    """Setup indices for charms.
+
+    This function must be idempotent as it is called by the initialization
+    section of migrate and may be called by upgrade scripts.
+
+    Returns the index if created.  If the index already exists None is
+    returned.
+    """
+
+    # Use ensure_index as it will not recreate the index if it already
+    # exists.
+    return charms.ensure_index(
+        [
+            ('owner', pymongo.DESCENDING),
+            ('series', pymongo.DESCENDING),
+            ('name', pymongo.DESCENDING),
+            ('store_data.revision', pymongo.DESCENDING),
+        ],
+        unique=True,
+        name='owner_series_name_revision',
+    )
+
+
 class MigrationBeforeExodus(Exception):
     pass
 
@@ -147,14 +203,10 @@
             else:
                 pass  # Must be a helper file or something, let's ignore it.
 
-    @classmethod
-    def setup_qa_data(cls, db):
-        for category_dict in iter_categories():
-            db.qa.insert(category_dict)
-
     def initialize(self, datastore):
         datastore.version_datastore()
-        self.setup_qa_data(datastore.db)
+        setup_mongo_indices(datastore.db.charms)
+        setup_qa_data(datastore.db)
 
     def ensure_initialized(self, datastore, init=False):
         if datastore.current_version is not None:
@@ -170,7 +222,7 @@
     def version_path(self, description, version):
         filename = "{0}_{1}.py".format(
             str(version).zfill(3),
-            str_to_filename(description)
+            str_to_filename(description),
         )
         path = join(self.versions_dir, filename)
         return path, filename
@@ -206,6 +258,13 @@
                 self.iter_versions(current)]
 
     def _check_exodus(self, version_info):
+        """Check the rules for running an exodus.
+
+        * There can be only one exodus in the set of tranformations to be run.
+        * An exodus must be first followed by one or more migrations.
+
+        May raise MigrationBeforeExodus or MultipleExodus.
+        """
         exodus_seen = False
         migration_seen = False
         for num, filename, is_exodus in version_info: