def update_attributes(cls, context, instance_id, username, hostname,
                          user_attrs):
        load_and_verify(context, instance_id)
        client = create_guest_client(context, instance_id)

        user_changed = user_attrs.get('name')
        host_changed = user_attrs.get('host')

        validate = guest_models.MySQLUser()
        if host_changed:
            validate.host = host_changed
        if user_changed:
            validate.name = user_changed

        user = user_changed or username
        host = host_changed or hostname
        userhost = "%[email protected]%s" % (user, host)
        if user_changed or host_changed:
            existing_users, _nadda = Users.load_with_client(
                client,
                limit=1,
                marker=userhost,
                include_marker=True)
            if (len(existing_users) > 0 and
                    existing_users[0].name == user and
                    existing_users[0].host == host):
                raise exception.UserAlreadyExists(name=user,
                                                  host=host)
        client.update_attributes(username, hostname, user_attrs)

def load_via_context(cls, context, instance_id):
    """Creates guest and fetches pagination arguments from the context."""
    load_and_verify(context, instance_id)
    limit = utils.pagination_limit(context.limit, cls.DEFAULT_LIMIT)
    client = create_guest_client(context, instance_id)
    # The REST API standard dictates that we *NEVER* include the marker.
    return cls.load_with_client(client=client, limit=limit,
                                marker=context.marker, include_marker=False)

 def access(cls, context, instance_id, username, hostname):
     load_and_verify(context, instance_id)
     client = create_guest_client(context, instance_id)
     databases = client.list_access(username, hostname)
     dbs = []
     for db in databases:
         dbs.append(Schema(name=db['_name'],
                           collate=db['_collate'],
                           character_set=db['_character_set']))
     return UserAccess(dbs)

 def change_password(cls, context, instance_id, users):
     load_and_verify(context, instance_id)
     client = create_guest_client(context, instance_id)
     change_users = []
     for user in users:
         change_user = {'name': user.name,
                        'host': user.host,
                        'password': user.password,
                        }
         change_users.append(change_user)
     client.change_passwords(change_users)

 def create(cls, context, instance_id, schemas):
     load_and_verify(context, instance_id)
     client = create_guest_client(context, instance_id)
     for schema in schemas:
         schema_name = schema['_name']
         existing_schema, _nadda = Schemas.load_with_client(
             client,
             limit=1,
             marker=schema_name,
             include_marker=True)
         if (len(existing_schema) > 0 and
                 str(existing_schema[0].name) == str(schema_name)):
             raise exception.DatabaseAlreadyExists(name=schema_name)
     return client.create_database(schemas)

 def load(cls, context, instance_id, username, hostname):
     load_and_verify(context, instance_id)
     validate = guest_models.MySQLUser()
     validate.name = username
     validate.host = hostname
     client = create_guest_client(context, instance_id)
     found_user = client.get_user(username=username, hostname=hostname)
     if not found_user:
         return None
     database_names = [{'name': db['_name']}
                       for db in found_user['_databases']]
     return cls(found_user['_name'],
                found_user['_host'],
                found_user['_password'],
                database_names)

    def delete(cls, context, instance_id, user):
        load_and_verify(context, instance_id)

        with StartNotification(context, instance_id=instance_id,
                               username=user):
            create_guest_client(context, instance_id).delete_user(user)

 def revoke(cls, context, instance_id, username, hostname, database):
     load_and_verify(context, instance_id)
     client = create_guest_client(context, instance_id)
     client.revoke_access(username, hostname, database)

 def grant(cls, context, instance_id, username, hostname, databases):
     load_and_verify(context, instance_id)
     client = create_guest_client(context, instance_id)
     client.grant_access(username, hostname, databases)

 def delete(cls, context, instance_id, user):
     load_and_verify(context, instance_id)
     create_guest_client(context, instance_id).delete_user(user)

 def create_guest_client(self, context, instance_id):
     common_utils.load_and_verify(context, instance_id)
     return remote.create_guest_client(context, instance_id)