gistfile1.py

from collections import defaultdict
from elements.element import ElementChanges
from elements.change_set import ElementChangeSet

# Step 1
# Get ElementChanges entities for the 
membership_key_str = ''

membership = db.get(membership_key_str)
ecs = ElementChanges.query(ancestor=ndb.Key('DraftGroup', membership.key().id())).fetch(100)
for ec in ecs:
  print 'TemplateID: %s | Changes: %s' % (ec.key.pairs()[1][1], len(ec.changes))

# Step 2 
# Get a list of TVE ElementChangeSets for the membership 
ecss = base.fetch_entities(ElementChangeSet.gql('where membership=:1', membership))
ecss_with_template = []
for cs in ecss:
  if '~' in cs.element_keyname:
    ecss_with_template.append(cs)

print len(ecss_with_template)

# Step 3
# Get the unique list of template ids represented in the TVE ElementChangeSets list
cs_elems_by_template = defaultdict(list)
for cs in ecss_with_template:
  cs_elems_by_template[cs.element_keyname.split('~')[1]].append(cs.element_keyname)
print cs_elems_by_template.keys()

# Step 4
# Remove any ElementChanges entities for template ids not in the 
# TVE ElementChangeSets list
ecs_to_delete = []
for ec in ecs:
  if ec.key.pairs()[1][1] not in cs_elems_by_template.keys():
    ecs_to_delete.append(ec.key)

if ecs_to_delete:
  print ecs_to_delete
  ndb.delete_multi(ecs_to_delete)

# Step 5 Rebuild any remaining ElementChanges using the TVE ElementChangeSest list
ecs_to_save = []
for ec in ecs:
  templateid = ec.key.pairs()[1][1]
  if templateid in cs_elems_by_template.keys() and len(ec.changes) != len(cs_elems_by_template[templateid]):
    ec.changes = cs_elems_by_template[templateid]
    ecs_to_save.append(ec)

if ecs_to_save:
  print ecs_to_save
  ndb.put_multi(ecs_to_save)