mongo-python-driver/pymongo/command_cursor.py

# Copyright 2014 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 pymongo import helpers, message
from pymongo.errors import AutoReconnect


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

    def __init__(self, collection, cursor_info, conn_id, compile_re=True):
        """Create a new command cursor.
        """
        self.__collection = collection
        self.__id = cursor_info['id']
        self.__conn_id = conn_id
        self.__data = deque(cursor_info['firstBatch'])
        self.__decode_opts = (
            collection.database.connection.document_class,
            collection.database.connection.tz_aware,
            collection.uuid_subtype,
            compile_re
        )
        self.__retrieved = cursor_info.get('_retrieved', 0)
        self.__batch_size = 0
        self.__killed = False

    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:
            client = self.__collection.database.connection
            if self.__conn_id is not None:
                client.close_cursor(self.__id, self.__conn_id)
            else:
                client.close_cursor(self.__id)
        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, (int, long)):
            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, msg):
        """Send a getmore message and handle the response.
        """
        client = self.__collection.database.connection
        try:
            res = client._send_message_with_response(
                msg, _connection_to_use=self.__conn_id)
            self.__conn_id, (response, dummy0, dummy1) = res
        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:
            response = helpers._unpack_response(response,
                                                self.__id,
                                                *self.__decode_opts)
        except AutoReconnect:
            # Don't send kill cursors to another server after a "not master"
            # error. It's completely pointless.
            self.__killed = True
            client.disconnect()
            raise
        self.__id = response["cursor_id"]

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

        self.__retrieved += response["number_returned"]
        self.__data = deque(response["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(
                message.get_more(self.__collection.full_name,
                                 self.__batch_size, self.__id))

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

        return len(self.__data)

    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

    def __enter__(self):
        return self

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