mongo-ruby-driver/lib/mongo/cursor.rb

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# --
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# Copyright (C) 2008-2009 10gen Inc.
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#
# 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
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#
# http://www.apache.org/licenses/LICENSE-2.0
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#
# 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.
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# ++
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require 'mongo/message'
require 'mongo/util/byte_buffer'
require 'mongo/util/bson'
module XGen
module Mongo
module Driver
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# A cursor over query results. Returned objects are hashes.
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class Cursor
include Enumerable
RESPONSE_HEADER_SIZE = 20
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attr_reader :db, :collection, :query
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def initialize(db, collection, query)
@db, @collection, @query = db, collection, query
@num_to_return = @query.number_to_return || 0
@cache = []
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@closed = false
@can_call_to_a = true
@query_run = false
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@rows = nil
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end
def closed?; @closed; end
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# Internal method, not for general use. Return +true+ if there are
# more records to retrieve. We do not check @num_to_return; #each is
# responsible for doing that.
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def more?
num_remaining > 0
end
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# Return the next object or nil if there are no more. Raises an error
# if necessary.
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def next_object
refill_via_get_more if num_remaining == 0
o = @cache.shift
if o && o['$err']
err = o['$err']
# If the server has stopped being the master (e.g., it's one of a
# pair but it has died or something like that) then we close that
# connection. If the db has auto connect option and a pair of
# servers, next request will re-open on master server.
@db.close if err == "not master"
raise err
end
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o
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end
# Iterate over each object, yielding it to the given block. At most
# @num_to_return records are returned (or all of them, if
# @num_to_return is 0).
#
# If #to_a has already been called then this method uses the array
# that we store internally. In that case, #each can be called multiple
# times because it re-uses that array.
#
# You can call #each after calling #to_a (multiple times even, because
# it will use the internally-stored array), but you can't call #to_a
# after calling #each unless you also called it before calling #each.
# If you try to do that, an error will be raised.
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def each
if @rows # Already turned into an array
@rows.each { |row| yield row }
else
num_returned = 0
while more? && (@num_to_return <= 0 || num_returned < @num_to_return)
yield next_object()
num_returned += 1
end
@can_call_to_a = false
end
end
# Return all of the rows (up to the +num_to_return+ value specified in
# #new) as an array. Calling this multiple times will work fine; it
# always returns the same array.
#
# Don't use this if you're expecting large amounts of data, of course.
# All of the returned rows are kept in an array stored in this object
# so it can be reused.
#
# You can call #each after calling #to_a (multiple times even, because
# it will use the internally-stored array), but you can't call #to_a
# after calling #each unless you also called it before calling #each.
# If you try to do that, an error will be raised.
def to_a
return @rows if @rows
raise "can't call Cursor#to_a after calling Cursor#each" unless @can_call_to_a
@rows = []
num_returned = 0
while more? && (@num_to_return <= 0 || num_returned < @num_to_return)
@rows << next_object()
num_returned += 1
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end
@rows
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end
# Returns an explain plan record.
def explain
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old_val = @query.explain
@query.explain = true
c = Cursor.new(@db, @collection, @query)
explanation = c.next_object
c.close
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@query.explain = old_val
explanation
end
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# Close the cursor.
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#
# Note: if a cursor is read until exhausted (read until OP_QUERY or
# OP_GETMORE returns zero for the cursor id), there is no need to
# close it by calling this method.
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def close
@db.send_to_db(KillCursorsMessage.new(@cursor_id)) if @cursor_id
@cache = []
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@cursor_id = 0
@closed = true
end
protected
def read_all
read_message_header
read_response_header
read_objects_off_wire
end
def read_objects_off_wire
while doc = next_object_on_wire
@cache << doc
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end
end
def read_message_header
MessageHeader.new.read_header(@db.socket)
end
def read_response_header
header_buf = ByteBuffer.new
header_buf.put_array(@db.socket.recv(RESPONSE_HEADER_SIZE).unpack("C*"))
raise "Short read for DB response header; expected #{RESPONSE_HEADER_SIZE} bytes, saw #{header_buf.length}" unless header_buf.length == RESPONSE_HEADER_SIZE
header_buf.rewind
@result_flags = header_buf.get_int
@cursor_id = header_buf.get_long
@starting_from = header_buf.get_int
@n_returned = header_buf.get_int
@n_remaining = @n_returned
end
def num_remaining
refill_via_get_more if @cache.length == 0
@cache.length
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end
private
def next_object_on_wire
send_query_if_needed
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# if @n_remaining is 0 but we have a non-zero cursor, there are more
# to fetch, so do a GetMore operation, but don't do it here - do it
# when someone pulls an object out of the cache and it's empty
return nil if @n_remaining == 0
object_from_stream
end
def refill_via_get_more
send_query_if_needed
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return if @cursor_id == 0
@db.send_to_db(GetMoreMessage.new(@db.name, @collection.name, @cursor_id))
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read_all
end
def object_from_stream
buf = ByteBuffer.new
buf.put_array(@db.socket.recv(4).unpack("C*"))
buf.rewind
size = buf.get_int
buf.put_array(@db.socket.recv(size-4).unpack("C*"), 4)
@n_remaining -= 1
buf.rewind
BSON.new(@db).deserialize(buf)
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end
def send_query_if_needed
# Run query first time we request an object from the wire
unless @query_run
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@db.send_query_message(QueryMessage.new(@db.name, @collection.name, @query))
@query_run = true
read_all
end
end
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def to_s
"DBResponse(flags=#@result_flags, cursor_id=#@cursor_id, start=#@starting_from, n_returned=#@n_returned)"
end
end
end
end
end