'Returns a dictionary of release_id => commit metadata,
where each commit metadata dict contains commit_count
and an array of authors.
e.g.
1: {
\'latest_commit\': <Commit id=1>,
\'authors\': [<User id=1>, <User id=2>]'

def _get_deploy_metadata(self, item_list, user):

    deploy_ids = set((o.last_deploy_id for o in item_list if o.last_deploy_id))
    if deploy_ids:
        deploy_list = list(Deploy.objects.filter(id__in=deploy_ids))
        deploys = {d.id: c for (d, c) in izip(deploy_list, serialize(deploy_list, user))}
    else:
        deploys = {}
    result = {}
    for item in item_list:
        result[item] = {'last_deploy': deploys.get(item.last_deploy_id)}
    return result
