53ad43fedc
Can be passed to find/find_one, which in turn is passed to cursor. It is an optional block that makes it easier to turn documents that are returned into hashes.
cursor = collection.find({...}, :transformer => Proc.new { |doc| User.load(doc) })
cursor.next # returns instance of User instead of ordered hash
This will allow MongoMapper, ToyStore and other object mappers to take better advantage of Cursors. No more calling to_a and mapping to instances.
455 lines
14 KiB
Ruby
455 lines
14 KiB
Ruby
# encoding: UTF-8
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# Copyright (C) 2008-2011 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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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 Mongo::Conversions
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include Enumerable
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attr_reader :collection, :selector, :fields,
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:order, :hint, :snapshot, :timeout,
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:full_collection_name, :transformer
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# Create a new cursor.
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#
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# Note: cursors are created when executing queries using [Collection#find] and other
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# similar methods. Application developers shouldn't have to create cursors manually.
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#
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# @return [Cursor]
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#
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# @core cursors constructor_details
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def initialize(collection, opts={})
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@db = collection.db
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@collection = collection
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@connection = @db.connection
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@logger = @connection.logger
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@selector = opts[:selector] || {}
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@fields = convert_fields_for_query(opts[:fields])
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@skip = opts[:skip] || 0
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@limit = opts[:limit] || 0
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@order = opts[:order]
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@hint = opts[:hint]
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@snapshot = opts[:snapshot]
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@timeout = opts.fetch(:timeout, true)
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@explain = opts[:explain]
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@socket = opts[:socket]
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@tailable = opts[:tailable] || false
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@closed = false
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@query_run = false
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@transformer = opts[:transformer]
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batch_size(opts[:batch_size] || 0)
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@full_collection_name = "#{@collection.db.name}.#{@collection.name}"
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@cache = []
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@returned = 0
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if @collection.name =~ /^\$cmd/ || @collection.name =~ /^system/
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@command = true
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else
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@command = false
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end
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end
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# Get the next document specified the cursor options.
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#
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# @return [Hash, Nil] the next document or Nil if no documents remain.
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def next_document
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refresh if @cache.length == 0
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doc = @cache.shift
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if doc && doc['$err']
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err = doc['$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. The next request will re-open on master server.
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if err == "not master"
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@connection.close
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raise ConnectionFailure, err
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end
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raise OperationFailure, err
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end
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if @transformer.nil?
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doc
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else
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@transformer.call(doc) if doc
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end
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end
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alias :next :next_document
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# Reset this cursor on the server. Cursor options, such as the
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# query string and the values for skip and limit, are preserved.
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def rewind!
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close
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@cache.clear
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@cursor_id = nil
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@closed = false
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@query_run = false
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@n_received = nil
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true
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end
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# Determine whether this cursor has any remaining results.
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#
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# @return [Boolean]
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def has_next?
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num_remaining > 0
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end
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# Get the size of the result set for this query.
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#
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# @param [Boolean] whether of not to take notice of skip and limit
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#
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# @return [Integer] the number of objects in the result set for this query.
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#
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# @raise [OperationFailure] on a database error.
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def count(skip_and_limit = false)
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command = BSON::OrderedHash["count", @collection.name, "query", @selector]
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if skip_and_limit
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command.merge!(BSON::OrderedHash["limit", @limit]) if @limit != 0
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command.merge!(BSON::OrderedHash["skip", @skip]) if @skip != 0
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end
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command.merge!(BSON::OrderedHash["fields", @fields])
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response = @db.command(command)
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return response['n'].to_i if Mongo::Support.ok?(response)
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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 this cursor's results.
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#
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# This method overrides any sort order specified in the Collection#find
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# method, and only the last sort applied has an effect.
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#
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# @param [Symbol, Array] key_or_list either 1) a key to sort by or 2)
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# an array of [key, direction] pairs to sort by. Direction should
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# be specified as Mongo::ASCENDING (or :ascending / :asc) or Mongo::DESCENDING (or :descending / :desc)
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#
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# @raise [InvalidOperation] if this cursor has already been used.
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#
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# @raise [InvalidSortValueError] if the specified order is invalid.
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def sort(key_or_list, direction=nil)
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check_modifiable
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if !direction.nil?
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order = [[key_or_list, direction]]
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else
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order = key_or_list
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end
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@order = order
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self
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end
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# Limit the number of results to be returned by this cursor.
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#
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# This method overrides any limit specified in the Collection#find method,
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# and only the last limit applied has an effect.
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#
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# @return [Integer] the current number_to_return if no parameter is given.
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#
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# @raise [InvalidOperation] if this cursor has already been used.
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#
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# @core limit limit-instance_method
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def limit(number_to_return=nil)
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return @limit unless number_to_return
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check_modifiable
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@limit = number_to_return
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self
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end
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# Skips the first +number_to_skip+ results of this cursor.
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# Returns the current number_to_skip if no parameter is given.
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#
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# This method overrides any skip specified in the Collection#find method,
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# and only the last skip applied has an effect.
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#
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# @return [Integer]
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#
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# @raise [InvalidOperation] if this cursor has already been used.
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def skip(number_to_skip=nil)
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return @skip unless number_to_skip
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check_modifiable
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@skip = number_to_skip
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self
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end
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# Set the batch size for server responses.
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#
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# Note that the batch size will take effect only on queries
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# where the number to be returned is greater than 100.
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#
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# @param [Integer] size either 0 or some integer greater than 1. If 0,
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# the server will determine the batch size.
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#
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# @return [Cursor]
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def batch_size(size=0)
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check_modifiable
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if size < 0 || size == 1
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raise ArgumentError, "Invalid value for batch_size #{size}; must be 0 or > 1."
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else
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@batch_size = size > @limit ? @limit : size
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end
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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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#
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# @yield passes each document to a block for processing.
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#
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# @example if 'comments' represents a collection of comments:
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# comments.find.each do |doc|
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# puts doc['user']
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# end
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def each
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#num_returned = 0
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#while has_next? && (@limit <= 0 || num_returned < @limit)
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while doc = next_document
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yield doc #next_document
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#num_returned += 1
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end
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end
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# Receive all the documents from this cursor as an array of hashes.
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#
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# Notes:
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#
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# If you've already started iterating over the cursor, the array returned
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# by this method contains only the remaining documents. See Cursor#rewind! if you
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# need to reset the cursor.
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#
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# Use of this method is discouraged - in most cases, it's much more
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# efficient to retrieve documents as you need them by iterating over the cursor.
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#
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# @return [Array] an array of documents.
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def to_a
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super
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end
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# Get the explain plan for this cursor.
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#
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# @return [Hash] a document containing the explain plan for this cursor.
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#
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# @core explain explain-instance_method
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def explain
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c = Cursor.new(@collection, query_options_hash.merge(:limit => -@limit.abs, :explain => true))
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explanation = c.next_document
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c.close
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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 Mongo::Constants::OP_QUERY or
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# Mongo::Constants::OP_GETMORE returns zero for the cursor id), there is no need to
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# close it manually.
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#
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# Note also: Collection#find takes an optional block argument which can be used to
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# ensure that your cursors get closed.
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#
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# @return [True]
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def close
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if @cursor_id && @cursor_id != 0
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message = BSON::ByteBuffer.new([0, 0, 0, 0])
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message.put_int(1)
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message.put_long(@cursor_id)
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@logger.debug("MONGODB cursor.close #{@cursor_id}") if @logger
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@connection.send_message(Mongo::Constants::OP_KILL_CURSORS, message, nil)
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end
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@cursor_id = 0
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@closed = true
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end
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# Is this cursor closed?
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#
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# @return [Boolean]
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def closed?; @closed; end
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# Returns an integer indicating which query options have been selected.
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#
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# @return [Integer]
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#
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# @see http://www.mongodb.org/display/DOCS/Mongo+Wire+Protocol#MongoWireProtocol-Mongo::Constants::OPQUERY
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# The MongoDB wire protocol.
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def query_opts
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opts = 0
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opts |= Mongo::Constants::OP_QUERY_NO_CURSOR_TIMEOUT unless @timeout
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opts |= Mongo::Constants::OP_QUERY_SLAVE_OK if @connection.slave_ok?
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opts |= Mongo::Constants::OP_QUERY_TAILABLE if @tailable
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opts
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end
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# Get the query options for this Cursor.
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#
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# @return [Hash]
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def query_options_hash
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{ :selector => @selector,
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:fields => @fields,
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:skip => @skip_num,
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:limit => @limit_num,
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:order => @order,
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:hint => @hint,
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:snapshot => @snapshot,
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:timeout => @timeout }
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end
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# Clean output for inspect.
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def inspect
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"<Mongo::Cursor:0x#{object_id.to_s(16)} namespace='#{@db.name}.#{@collection.name}' " +
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"@selector=#{@selector.inspect}>"
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end
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private
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# Convert the +:fields+ parameter from a single field name or an array
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# of fields names to a hash, with the field names for keys and '1' for each
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# value.
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def convert_fields_for_query(fields)
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case fields
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when String, Symbol
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{fields => 1}
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when Array
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return nil if fields.length.zero?
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fields.each_with_object({}) { |field, hash| hash[field] = 1 }
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when Hash
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return fields
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end
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end
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# Return the number of documents remaining for this cursor.
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def num_remaining
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refresh if @cache.length == 0
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@cache.length
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end
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def refresh
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return if send_initial_query || @cursor_id.zero?
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message = BSON::ByteBuffer.new([0, 0, 0, 0])
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# DB name.
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BSON::BSON_RUBY.serialize_cstr(message, "#{@db.name}.#{@collection.name}")
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# Number of results to return.
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if @limit > 0
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limit = @limit - @returned
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if @batch_size > 0
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limit = limit < @batch_size ? limit : @batch_size
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end
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message.put_int(limit)
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else
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message.put_int(@batch_size)
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end
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# Cursor id.
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message.put_long(@cursor_id)
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@logger.debug("MONGODB cursor.refresh() for cursor #{@cursor_id}") if @logger
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results, @n_received, @cursor_id = @connection.receive_message(
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Mongo::Constants::OP_GET_MORE, message, nil, @socket, @command)
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@returned += @n_received
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@cache += results
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close_cursor_if_query_complete
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end
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# Run query the first time we request an object from the wire
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# TODO: should we be calling instrument_payload even if logging
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# is disabled?
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def send_initial_query
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if @query_run
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false
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else
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message = construct_query_message
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@connection.instrument(:find, instrument_payload) do
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results, @n_received, @cursor_id = @connection.receive_message(
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Mongo::Constants::OP_QUERY, message, nil, @socket, @command)
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@returned += @n_received
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@cache += results
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@query_run = true
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close_cursor_if_query_complete
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end
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true
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end
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end
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def construct_query_message
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message = BSON::ByteBuffer.new
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message.put_int(query_opts)
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BSON::BSON_RUBY.serialize_cstr(message, "#{@db.name}.#{@collection.name}")
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message.put_int(@skip)
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message.put_int(@limit)
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spec = query_contains_special_fields? ? construct_query_spec : @selector
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message.put_binary(BSON::BSON_CODER.serialize(spec, false).to_s)
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message.put_binary(BSON::BSON_CODER.serialize(@fields, false).to_s) if @fields
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message
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end
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def instrument_payload
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log = { :database => @db.name, :collection => @collection.name, :selector => selector }
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log[:fields] = @fields if @fields
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log[:skip] = @skip if @skip && (@skip > 0)
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log[:limit] = @limit if @limit && (@limit > 0)
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log[:order] = @order if @order
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log
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end
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def construct_query_spec
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return @selector if @selector.has_key?('$query')
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spec = BSON::OrderedHash.new
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spec['$query'] = @selector
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spec['$orderby'] = Mongo::Support.format_order_clause(@order) if @order
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spec['$hint'] = @hint if @hint && @hint.length > 0
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spec['$explain'] = true if @explain
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spec['$snapshot'] = true if @snapshot
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spec
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end
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# Returns true if the query contains order, explain, hint, or snapshot.
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def query_contains_special_fields?
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@order || @explain || @hint || @snapshot
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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)"
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end
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def close_cursor_if_query_complete
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if @limit > 0 && @returned >= @limit
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close
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end
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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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