270 lines
8.2 KiB
Ruby
270 lines
8.2 KiB
Ruby
# Copyright (C) 2008-2009 10gen Inc.
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#
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# Licensed under the Apache License, Version 2.0 (the "License");
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# you may not use this file except in compliance with the License.
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# You may obtain a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS,
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# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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# See the License for the specific language governing permissions and
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# limitations under the License.
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require 'mongo/message'
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require 'mongo/util/byte_buffer'
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require 'mongo/util/bson'
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module Mongo
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# A cursor over query results. Returned objects are hashes.
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class Cursor
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include Enumerable
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RESPONSE_HEADER_SIZE = 20
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attr_reader :db, :collection, :query
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# Create a new cursor.
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#
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# Should not be called directly by application developers.
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def initialize(db, collection, query, admin=false)
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@db, @collection, @query, @admin = db, collection, query, admin
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@cache = []
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@closed = false
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@query_run = false
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end
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# Return the next object or nil if there are no more. Raises an error
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# if necessary.
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def next_object
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refill_via_get_more if num_remaining == 0
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o = @cache.shift
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if o && o['$err']
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err = o['$err']
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# If the server has stopped being the master (e.g., it's one of a
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# pair but it has died or something like that) then we close that
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# connection. If the db has auto connect option and a pair of
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# servers, next request will re-open on master server.
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@db.close if err == "not master"
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raise err
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end
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o
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end
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# Get the size of the results set for this query.
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#
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# Returns the number of objects in the results set for this query. Does
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# not take limit and skip into account. Raises OperationFailure on a
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# database error.
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def count
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command = OrderedHash["count", @collection.name,
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"query", @query.selector,
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"fields", @query.fields()]
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response = @db.db_command(command)
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return response['n'].to_i if response['ok'] == 1
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return 0 if response['errmsg'] == "ns missing"
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raise OperationFailure, "Count failed: #{response['errmsg']}"
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end
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# Sort the results of the query with a hash of keys and orders
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#
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# Sorts should be formed as such:
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# {:name=>-1} (sort by name, descending) OR {:name=>1} (sort by name, ascending)
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# options are stackable, with the last option being the priority, i.e.:
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# {:name => -1, :age => 1} (name descending, age asending)
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def sort(order_hash = {})
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raise InvalidOperation, "can't call Cursor#sort on a used cursor" if @query_run
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@query.order_by = OrderedHash[order_hash]
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self
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end
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# Limits the number of results to be returned by this cursor.
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#
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# Note: this method overrides any limit specified in the #find method.
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def limit(number_to_return)
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check_modifiable
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raise ArgumentError, "limit requires an integer" unless number_to_return.is_a? Integer
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@query.number_to_return = number_to_return
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return self
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end
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# Skips the first +number_to_skip+ results of this cursor.
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#
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# Note: this method overrides any offset specified in the #find method.
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def skip(number_to_skip)
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check_modifiable
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raise ArgumentError, "skip requires an integer" unless number_to_skip.is_a? Integer
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@query.number_to_skip = number_to_skip
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return self
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end
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# Iterate over each document in this cursor, yielding it to the given
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# block.
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#
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# Iterating over an entire cursor will close it.
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def each
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num_returned = 0
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while more? && (@query.number_to_return <= 0 || num_returned < @query.number_to_return)
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yield next_object()
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num_returned += 1
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end
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end
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# Return all of the documents in this cursor as an array of hashes.
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#
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# Raises InvalidOperation if this cursor has already been used (including
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# any previous calls to this method).
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#
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# Use of this method is discouraged - iterating over a cursor is much
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# more efficient in most cases.
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def to_a
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raise InvalidOperation, "can't call Cursor#to_a on a used cursor" if @query_run
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rows = []
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num_returned = 0
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while more? && (@query.number_to_return <= 0 || num_returned < @query.number_to_return)
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rows << next_object()
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num_returned += 1
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end
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rows
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end
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# Returns an explain plan record for this cursor.
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def explain
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limit = @query.number_to_return
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@query.explain = true
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@query.number_to_return = -limit.abs
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c = Cursor.new(@db, @collection, @query)
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explanation = c.next_object
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c.close
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@query.explain = false
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@query.number_to_return = limit
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explanation
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end
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# Close the cursor.
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#
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# Note: if a cursor is read until exhausted (read until OP_QUERY or
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# OP_GETMORE returns zero for the cursor id), there is no need to
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# close it by calling this method.
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#
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# Collection#find takes an optional block argument which can be used to
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# ensure that your cursors get closed. See the documentation for
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# Collection#find for details.
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def close
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@db.send_to_db(KillCursorsMessage.new(@cursor_id)) if @cursor_id
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@cache = []
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@cursor_id = 0
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@closed = true
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end
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# Returns true if this cursor is closed, false otherwise.
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def closed?; @closed; end
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private
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def read_all
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read_message_header
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read_response_header
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read_objects_off_wire
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end
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def read_objects_off_wire
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while doc = next_object_on_wire
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@cache << doc
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end
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end
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def read_message_header
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MessageHeader.new.read_header(@db)
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end
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def read_response_header
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header_buf = ByteBuffer.new
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header_buf.put_array(@db.receive_full(RESPONSE_HEADER_SIZE).unpack("C*"))
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raise "Short read for DB response header; expected #{RESPONSE_HEADER_SIZE} bytes, saw #{header_buf.length}" unless header_buf.length == RESPONSE_HEADER_SIZE
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header_buf.rewind
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@result_flags = header_buf.get_int
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@cursor_id = header_buf.get_long
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@starting_from = header_buf.get_int
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@n_returned = header_buf.get_int
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@n_remaining = @n_returned
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end
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def num_remaining
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refill_via_get_more if @cache.length == 0
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@cache.length
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end
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# Internal method, not for general use. Return +true+ if there are
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# more records to retrieve. We do not check @query.number_to_return;
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# #each is responsible for doing that.
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def more?
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num_remaining > 0
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end
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def next_object_on_wire
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# if @n_remaining is 0 but we have a non-zero cursor, there are more
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# to fetch, so do a GetMore operation, but don't do it here - do it
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# when someone pulls an object out of the cache and it's empty
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return nil if @n_remaining == 0
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object_from_stream
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end
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def refill_via_get_more
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if send_query_if_needed or @cursor_id == 0
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return
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end
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@db._synchronize {
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@db.send_to_db(GetMoreMessage.new(@admin ? 'admin' : @db.name, @collection.name, @cursor_id))
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read_all
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}
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end
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def object_from_stream
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buf = ByteBuffer.new
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buf.put_array(@db.receive_full(4).unpack("C*"))
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buf.rewind
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size = buf.get_int
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buf.put_array(@db.receive_full(size - 4).unpack("C*"), 4)
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@n_remaining -= 1
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buf.rewind
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BSON.new.deserialize(buf)
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end
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def send_query_if_needed
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# Run query first time we request an object from the wire
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if @query_run
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false
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else
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@db._synchronize {
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@db.send_query_message(QueryMessage.new(@admin ? 'admin' : @db.name, @collection.name, @query))
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@query_run = true
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read_all
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}
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true
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end
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end
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def to_s
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"DBResponse(flags=#@result_flags, cursor_id=#@cursor_id, start=#@starting_from, n_returned=#@n_returned)"
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end
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def check_modifiable
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if @query_run || @closed
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raise InvalidOperation, "Cannot modify the query once it has been run or closed."
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end
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end
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end
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end
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