mongo-python-driver/pymongo/command_cursor.py

# Copyright 2014-2015 MongoDB, Inc.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

"""CommandCursor class to iterate over command results."""

from collections import deque

from bson.py3compat import integer_types
from pymongo import helpers
from pymongo.errors import AutoReconnect, CursorNotFound, NotMasterError
from pymongo.message import _GetMore


class CommandCursor(object):
    """A cursor / iterator over command cursors.
    """

    def __init__(self, collection, cursor_info, address, retrieved=0):
        """Create a new command cursor.
        """
        self.__collection = collection
        self.__id = cursor_info['id']
        self.__address = address
        self.__data = deque(cursor_info['firstBatch'])
        self.__retrieved = retrieved
        self.__batch_size = 0
        self.__killed = False

        if "ns" in cursor_info:
            self.__ns = cursor_info["ns"]
        else:
            self.__ns = collection.full_name

    def __del__(self):
        if self.__id and not self.__killed:
            self.__die()

    def __die(self):
        """Closes this cursor.
        """
        if self.__id and not self.__killed:
            self.__collection.database.client.close_cursor(self.__id,
                                                           self.__address)
        self.__killed = True

    def close(self):
        """Explicitly close / kill this cursor. Required for PyPy, Jython and
        other Python implementations that don't use reference counting
        garbage collection.
        """
        self.__die()

    def batch_size(self, batch_size):
        """Limits the number of documents returned in one batch. Each batch
        requires a round trip to the server. It can be adjusted to optimize
        performance and limit data transfer.

        .. note:: batch_size can not override MongoDB's internal limits on the
           amount of data it will return to the client in a single batch (i.e
           if you set batch size to 1,000,000,000, MongoDB will currently only
           return 4-16MB of results per batch).

        Raises :exc:`TypeError` if `batch_size` is not an integer.
        Raises :exc:`ValueError` if `batch_size` is less than ``0``.

        :Parameters:
          - `batch_size`: The size of each batch of results requested.
        """
        if not isinstance(batch_size, integer_types):
            raise TypeError("batch_size must be an integer")
        if batch_size < 0:
            raise ValueError("batch_size must be >= 0")

        self.__batch_size = batch_size == 1 and 2 or batch_size
        return self

    def __send_message(self, operation):
        """Send a getmore message and handle the response.
        """
        client = self.__collection.database.client
        try:
            response = client._send_message_with_response(
                operation, address=self.__address)
        except AutoReconnect:
            # Don't try to send kill cursors on another socket
            # or to another server. It can cause a _pinValue
            # assertion on some server releases if we get here
            # due to a socket timeout.
            self.__killed = True
            raise

        try:
            doc = helpers._unpack_response(response.data,
                                           self.__id,
                                           self.__collection.codec_options)
        except CursorNotFound:
            self.__killed = True
            raise
        except NotMasterError:
            # Don't send kill cursors to another server after a "not master"
            # error. It's completely pointless.
            self.__killed = True
            client._reset_server_and_request_check(self.address)
            raise
        self.__id = doc["cursor_id"]

        assert doc["starting_from"] == self.__retrieved, (
            "Result batch started from %s, expected %s" % (
                doc['starting_from'], self.__retrieved))

        self.__retrieved += doc["number_returned"]
        self.__data = deque(doc["data"])

    def _refresh(self):
        """Refreshes the cursor with more data from the server.

        Returns the length of self.__data after refresh. Will exit early if
        self.__data is already non-empty. Raises OperationFailure when the
        cursor cannot be refreshed due to an error on the query.
        """
        if len(self.__data) or self.__killed:
            return len(self.__data)

        if self.__id:  # Get More
            self.__send_message(
                _GetMore(self.__ns, self.__batch_size, self.__id))

        else:  # Cursor id is zero nothing else to return
            self.__killed = True

        return len(self.__data)

    @property
    def alive(self):
        """Does this cursor have the potential to return more data?"""
        return bool(len(self.__data) or (not self.__killed))

    @property
    def cursor_id(self):
        """Returns the id of the cursor."""
        return self.__id

    @property
    def address(self):
        """The (host, port) of the server used, or None.

        .. versionadded:: 3.0
        """
        return self.__address

    def __iter__(self):
        return self

    def next(self):
        """Advance the cursor.
        """
        if len(self.__data) or self._refresh():
            coll = self.__collection
            return coll.database._fix_incoming(self.__data.popleft(), coll)
        else:
            raise StopIteration

    __next__ = next

    def __enter__(self):
        return self

    def __exit__(self, exc_type, exc_val, exc_tb):
        self.__die()