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# Copyright (C) 2008-2010 10gen 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.
module Mongo
# A cursor over query results. Returned objects are hashes.
class Cursor
include Mongo::Conversions
include Enumerable
attr_reader :collection, :selector, :admin, :fields,
:order, :hint, :snapshot, :timeout,
:full_collection_name
# Create a new cursor.
#
# Note: cursors are created when executing queries using [Collection#find] and other
# similar methods. Application developers shouldn't have to create cursors manually.
#
# @return [Cursor]
#
# @core cursors constructor_details
def initialize(collection, options={})
@db = collection.db
@collection = collection
@connection = @db.connection
@selector = convert_selector_for_query(options[:selector])
@fields = convert_fields_for_query(options[:fields])
@admin = options[:admin] || false
@skip = options[:skip] || 0
@limit = options[:limit] || 0
@order = options[:order]
@hint = options[:hint]
@snapshot = options[:snapshot]
@timeout = options[:timeout] || false
@explain = options[:explain]
@socket = options[:socket]
@full_collection_name = "#{@collection.db.name}.#{@collection.name}"
@cache = []
@closed = false
@query_run = false
end
# Get the next document specified the cursor options.
#
# @return [Hash, Nil] the next document or Nil if no documents remain.
def next_document
refill_via_get_more if num_remaining == 0
doc = @cache.shift
if doc && doc['$err']
err = doc['$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. The next request will re-open on master server.
if err == "not master"
raise ConnectionFailure, err
@connection.close
end
raise OperationFailure, err
end
doc
end
# Determine whether this cursor has any remaining results.
#
# @return [Boolean]
def has_next?
num_remaining > 0
end
# Get the size of the result set for this query.
#
# @return [Integer] the number of objects in the result set for this query. Does
# not take limit and skip into account.
#
# @raise [OperationFailure] on a database error.
def count
command = OrderedHash["count", @collection.name,
"query", @selector,
"fields", @fields]
response = @db.command(command)
return response['n'].to_i if response['ok'] == 1
return 0 if response['errmsg'] == "ns missing"
raise OperationFailure, "Count failed: #{response['errmsg']}"
end
# Sort this cursor's results.
#
# This method overrides any sort order specified in the Collection#find
# method, and only the last sort applied has an effect.
#
# @param [Symbol, Array] key_or_list either 1) a key to sort by or 2)
# an array of [key, direction] pairs to sort by. Direction should
# be specified as Mongo::ASCENDING (or :ascending / :asc) or Mongo::DESCENDING (or :descending / :desc)
#
# @raise [InvalidOperation] if this cursor has already been used.
#
# @raise [InvalidSortValueError] if the specified order is invalid.
def sort(key_or_list, direction=nil)
check_modifiable
if !direction.nil?
order = [[key_or_list, direction]]
else
order = key_or_list
end
@order = order
self
end
# Limit the number of results to be returned by this cursor.
#
# This method overrides any limit specified in the Collection#find method,
# and only the last limit applied has an effect.
#
# @return [Integer] the current number_to_return if no parameter is given.
#
# @raise [InvalidOperation] if this cursor has already been used.
#
# @core limit limit-instance_method
def limit(number_to_return=nil)
return @limit unless number_to_return
check_modifiable
raise ArgumentError, "limit requires an integer" unless number_to_return.is_a? Integer
@limit = number_to_return
self
end
# Skips the first +number_to_skip+ results of this cursor.
# Returns the current number_to_skip if no parameter is given.
#
# This method overrides any skip specified in the Collection#find method,
# and only the last skip applied has an effect.
#
# @return [Integer]
#
# @raise [InvalidOperation] if this cursor has already been used.
def skip(number_to_skip=nil)
return @skip unless number_to_skip
check_modifiable
raise ArgumentError, "skip requires an integer" unless number_to_skip.is_a? Integer
@skip = number_to_skip
self
end
# Iterate over each document in this cursor, yielding it to the given
# block.
#
# Iterating over an entire cursor will close it.
#
# @yield passes each document to a block for processing.
#
# @example if 'comments' represents a collection of comments:
# comments.find.each do |doc|
# puts doc['user']
# end
def each
num_returned = 0
while has_next? && (@limit <= 0 || num_returned < @limit)
yield next_document
num_returned += 1
end
end
# Receive all the documents from this cursor as an array of hashes.
#
# Note: use of this method is discouraged - in most cases, it's much more
# efficient to retrieve documents as you need them by iterating over the cursor.
#
# @return [Array] an array of documents.
#
# @raise [InvalidOperation] if this cursor has already been used or if
# this method has already been called on the cursor.
def to_a
raise InvalidOperation, "can't call Cursor#to_a on a used cursor" if @query_run
rows = []
num_returned = 0
while has_next? && (@limit <= 0 || num_returned < @limit)
rows << next_document
num_returned += 1
end
rows
end
# Get the explain plan for this cursor.
#
# @return [Hash] a document containing the explain plan for this cursor.
#
# @core explain explain-instance_method
def explain
c = Cursor.new(@collection, query_options_hash.merge(:limit => -@limit.abs, :explain => true))
explanation = c.next_document
c.close
explanation
end
# Close the cursor.
#
# Note: if a cursor is read until exhausted (read until Mongo::Constants::OP_QUERY or
# Mongo::Constants::OP_GETMORE returns zero for the cursor id), there is no need to
# close it manually.
#
# Note also: Collection#find takes an optional block argument which can be used to
# ensure that your cursors get closed.
#
# @return [True]
def close
if @cursor_id
message = ByteBuffer.new([0, 0, 0, 0])
message.put_int(1)
message.put_long(@cursor_id)
@connection.send_message(Mongo::Constants::OP_KILL_CURSORS, message, "cursor.close")
end
@cursor_id = 0
@closed = true
end
# Is this cursor closed?
#
# @return [Boolean]
def closed?; @closed; end
# Returns an integer indicating which query options have been selected.
#
# @return [Integer]
#
# @see http://www.mongodb.org/display/DOCS/Mongo+Wire+Protocol#MongoWireProtocol-Mongo::Constants::OPQUERY
# The MongoDB wire protocol.
def query_opts
timeout = @timeout ? 0 : Mongo::Constants::OP_QUERY_NO_CURSOR_TIMEOUT
slave_ok = @connection.slave_ok? ? Mongo::Constants::OP_QUERY_SLAVE_OK : 0
slave_ok + timeout
end
# Get the query options for this Cursor.
#
# @return [Hash]
def query_options_hash
{ :selector => @selector,
:fields => @fields,
:admin => @admin,
:skip => @skip_num,
:limit => @limit_num,
:order => @order,
:hint => @hint,
:snapshot => @snapshot,
:timeout => @timeout }
end
private
# Convert the +:fields+ parameter from a single field name or an array
# of fields names to a hash, with the field names for keys and '1' for each
# value.
def convert_fields_for_query(fields)
case fields
when String, Symbol
{fields => 1}
when Array
return nil if fields.length.zero?
returning({}) do |hash|
fields.each { |field| hash[field] = 1 }
end
when Hash
return fields
end
end
# Set the query selector hash. If the selector is a Code or String object,
# the selector will be used in a $where clause.
# See http://www.mongodb.org/display/DOCS/Server-side+Code+Execution
def convert_selector_for_query(selector)
case selector
when Hash
selector
when nil
{}
when String
{"$where" => Code.new(selector)}
when Code
{"$where" => selector}
end
end
# Returns true if the query contains order, explain, hint, or snapshot.
def query_contains_special_fields?
@order || @explain || @hint || @snapshot
end
# Return a number of documents remaining for this cursor.
def num_remaining
refill_via_get_more if @cache.length == 0
@cache.length
end
def refill_via_get_more
return if send_initial_query || @cursor_id.zero?
message = ByteBuffer.new([0, 0, 0, 0])
# DB name.
db_name = @admin ? 'admin' : @db.name
BSON_RUBY.serialize_cstr(message, "#{db_name}.#{@collection.name}")
# Number of results to return; db decides for now.
message.put_int(0)
# Cursor id.
message.put_long(@cursor_id)
results, @n_received, @cursor_id = @connection.receive_message(Mongo::Constants::OP_GET_MORE, message, "cursor.get_more()", @socket)
@cache += results
close_cursor_if_query_complete
end
# Run query the first time we request an object from the wire
def send_initial_query
if @query_run
false
else
message = construct_query_message
results, @n_received, @cursor_id = @connection.receive_message(Mongo::Constants::OP_QUERY, message,
(query_log_message if @connection.logger), @socket)
@cache += results
@query_run = true
close_cursor_if_query_complete
true
end
end
def construct_query_message
message = ByteBuffer.new
message.put_int(query_opts)
db_name = @admin ? 'admin' : @db.name
BSON_RUBY.serialize_cstr(message, "#{db_name}.#{@collection.name}")
message.put_int(@skip)
message.put_int(@limit)
selector = @selector
if query_contains_special_fields?
selector = selector_with_special_query_fields
end
message.put_array(BSON_CODER.serialize(selector, false).to_a)
message.put_array(BSON_CODER.serialize(@fields, false).to_a) if @fields
message
end
def query_log_message
"#{@admin ? 'admin' : @db.name}['#{@collection.name}'].find(#{@selector.inspect}, #{@fields ? @fields.inspect : '{}'})" +
"#{@skip != 0 ? ('.skip(' + @skip.to_s + ')') : ''}#{@limit != 0 ? ('.limit(' + @limit.to_s + ')') : ''}" +
"#{@order ? ('.sort(' + @order.inspect + ')') : ''}"
end
def selector_with_special_query_fields
sel = OrderedHash.new
sel['query'] = @selector
sel['orderby'] = formatted_order_clause if @order
sel['$hint'] = @hint if @hint && @hint.length > 0
sel['$explain'] = true if @explain
sel['$snapshot'] = true if @snapshot
sel
end
def formatted_order_clause
case @order
when String, Symbol then string_as_sort_parameters(@order)
when Array then array_as_sort_parameters(@order)
else
raise InvalidSortValueError, "Illegal sort clause, '#{@order.class.name}'; must be of the form " +
"[['field1', '(ascending|descending)'], ['field2', '(ascending|descending)']]"
end
end
def to_s
"DBResponse(flags=#@result_flags, cursor_id=#@cursor_id, start=#@starting_from)"
end
def close_cursor_if_query_complete
close if @limit > 0 && @n_received >= @limit
end
def check_modifiable
if @query_run || @closed
raise InvalidOperation, "Cannot modify the query once it has been run or closed."
end
end
end
end
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