A cursor over query results. Returned objects are hashes.
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
# File lib/mongo/cursor.rb, line 38 def initialize(collection, opts={}) @cursor_id = nil @db = collection.db @collection = collection @connection = @db.connection @logger = @connection.logger # Query selector @selector = opts[:selector] || {} # Special operators that form part of $query @order = opts[:order] @explain = opts[:explain] @hint = opts[:hint] @snapshot = opts[:snapshot] @max_scan = opts.fetch(:max_scan, nil) @return_key = opts.fetch(:return_key, nil) @show_disk_loc = opts.fetch(:show_disk_loc, nil) # Wire-protocol settings @fields = convert_fields_for_query(opts[:fields]) @skip = opts[:skip] || 0 @limit = opts[:limit] || 0 @tailable = opts[:tailable] || false @timeout = opts.fetch(:timeout, true) @options = 0 # Use this socket for the query @socket = opts[:socket] @closed = false @query_run = false @transformer = opts[:transformer] if value = opts[:read] Mongo::Support.validate_read_preference(value) else value = collection.read_preference end @read_preference = value.is_a?(Hash) ? value.dup : value batch_size(opts[:batch_size] || 0) @full_collection_name = "#{@collection.db.name}.#{@collection.name}" @cache = [] @returned = 0 if(!@timeout) add_option(OP_QUERY_NO_CURSOR_TIMEOUT) end if(@read_preference != :primary) add_option(OP_QUERY_SLAVE_OK) end if(@tailable) add_option(OP_QUERY_TAILABLE) end if @collection.name =~ /^\$cmd/ || @collection.name =~ /^system/ @command = true else @command = false end @checkin_read_pool = false @checkin_connection = false @read_pool = nil end
Add an option to the query options bitfield.
@param opt a valid query option
@raise InvalidOperation if this method is run after the cursor has bee
iterated for the first time.
@return [Integer] the current value of the options bitfield for this cursor.
@see www.mongodb.org/display/DOCS/Mongo+Wire+Protocol#MongoWireProtocol-Mongo::Constants::OPQUERY
# File lib/mongo/cursor.rb, line 376 def add_option(opt) check_modifiable @options |= opt @options end
Guess whether the cursor is alive on the server.
Note that this method only checks whether we have a cursor id. The cursor may still have timed out on the server. This will be indicated in the next call to #next.
@return [Boolean]
# File lib/mongo/cursor.rb, line 114 def alive? @cursor_id && @cursor_id != 0 end
Set the batch size for server responses.
Note that the batch size will take effect only on queries where the number to be returned is greater than 100.
This can not override MongoDB's limit on the amount of data it will return to the client. Depending on server version this can be 4-16mb.
@param [Integer] size either 0 or some integer greater than 1. If 0,
the server will determine the batch size.
@return [Cursor]
# File lib/mongo/cursor.rb, line 266 def batch_size(size=nil) return @batch_size unless size check_modifiable if size < 0 || size == 1 raise ArgumentError, "Invalid value for batch_size #{size}; must be 0 or > 1." else @batch_size = @limit != 0 && size > @limit ? @limit : size end self 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: Mongo::Collection#find takes an optional block argument which can be used to ensure that your cursors get closed.
@return [True]
# File lib/mongo/cursor.rb, line 335 def close if @cursor_id && @cursor_id != 0 message = BSON::ByteBuffer.new([0, 0, 0, 0]) message.put_int(1) message.put_long(@cursor_id) log(:debug, "Cursor#close #{@cursor_id}") @connection.send_message(Mongo::Constants::OP_KILL_CURSORS, message, :connection => :reader) end @cursor_id = 0 @closed = true end
Is this cursor closed?
@return [Boolean]
# File lib/mongo/cursor.rb, line 350 def closed? @closed end
Get the size of the result set for this query.
@param [Boolean] whether of not to take notice of skip and limit
@return [Integer] the number of objects in the result set for this query.
@raise [OperationFailure] on a database error.
# File lib/mongo/cursor.rb, line 180 def count(skip_and_limit = false) command = BSON::OrderedHash["count", @collection.name, "query", @selector] if skip_and_limit command.merge!(BSON::OrderedHash["limit", @limit]) if @limit != 0 command.merge!(BSON::OrderedHash["skip", @skip]) if @skip != 0 end command.merge!(BSON::OrderedHash["fields", @fields]) response = @db.command(command) return response['n'].to_i if Mongo::Support.ok?(response) return 0 if response['errmsg'] == "ns missing" raise OperationFailure.new("Count failed: #{response['errmsg']}", response['code'], response) 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
# File lib/mongo/cursor.rb, line 289 def each while doc = self.next yield doc end end
Get the explain plan for this cursor.
@return [Hash] a document containing the explain plan for this cursor.
@core explain explain-instance_method
# File lib/mongo/cursor.rb, line 316 def explain c = Cursor.new(@collection, query_options_hash.merge(:limit => -@limit.abs, :explain => true)) explanation = c.next_document c.close explanation end
Determine whether this cursor has any remaining results.
@return [Boolean]
# File lib/mongo/cursor.rb, line 169 def has_next? num_remaining > 0 end
Clean output for inspect.
# File lib/mongo/cursor.rb, line 418 def inspect "<Mongo::Cursor:0x#{object_id.to_s(16)} namespace='#{@db.name}.#{@collection.name}' " + "@selector=#{@selector.inspect} @cursor_id=#{@cursor_id}>" end
Limit the number of results to be returned by this cursor.
This method overrides any limit specified in the Mongo::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
# File lib/mongo/cursor.rb, line 229 def limit(number_to_return=nil) return @limit unless number_to_return check_modifiable @limit = number_to_return self end
Get the next document specified the cursor options.
@return [Hash, Nil] the next document or Nil if no documents remain.
# File lib/mongo/cursor.rb, line 121 def next if @cache.length == 0 if @query_run && (@options & OP_QUERY_EXHAUST != 0) close return nil else refresh end end 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.include?("not master") @connection.close raise ConnectionFailure.new(err, doc['code'], doc) end raise OperationFailure.new(err, doc['code'], doc) end if @transformer.nil? doc else @transformer.call(doc) if doc end end
Get the query options for this Cursor.
@return [Hash]
# File lib/mongo/cursor.rb, line 403 def query_options_hash { :selector => @selector, :fields => @fields, :skip => @skip, :limit => @limit, :order => @order, :hint => @hint, :snapshot => @snapshot, :timeout => @timeout, :max_scan => @max_scan, :return_key => @return_key, :show_disk_loc => @show_disk_loc } end
Returns an integer indicating which query options have been selected.
@return [Integer]
@see www.mongodb.org/display/DOCS/Mongo+Wire+Protocol#MongoWireProtocol-Mongo::Constants::OPQUERY The MongoDB wire protocol.
# File lib/mongo/cursor.rb, line 360 def query_opts warn "The method Cursor#query_opts has been deprecated " + "and will removed in v2.0. Use Cursor#options instead." @options end
Remove an option from the query options bitfield.
@param opt a valid query option
@raise InvalidOperation if this method is run after the cursor has bee
iterated for the first time.
@return [Integer] the current value of the options bitfield for this cursor.
@see www.mongodb.org/display/DOCS/Mongo+Wire+Protocol#MongoWireProtocol-Mongo::Constants::OPQUERY
# File lib/mongo/cursor.rb, line 393 def remove_option(opt) check_modifiable @options &= ~opt @options end
Reset this cursor on the server. Cursor options, such as the query string and the values for skip and limit, are preserved.
# File lib/mongo/cursor.rb, line 156 def rewind! close @cache.clear @cursor_id = nil @closed = false @query_run = false @n_received = nil true 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 Mongo::Collection#find method, and only the last skip applied has an effect.
@return [Integer]
@raise [InvalidOperation] if this cursor has already been used.
# File lib/mongo/cursor.rb, line 246 def skip(number_to_skip=nil) return @skip unless number_to_skip check_modifiable @skip = number_to_skip self end
Sort this cursor's results.
This method overrides any sort order specified in the Mongo::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 2)
an array of [key, direction] pairs to sort by or 3) a hash of field => 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.
# File lib/mongo/cursor.rb, line 210 def sort(order, direction=nil) check_modifiable order = [[order, direction]] unless direction.nil? @order = order self end
Receive all the documents from this cursor as an array of hashes.
Notes:
If you've already started iterating over the cursor, the array returned by this method contains only the remaining documents. See #rewind! if you need to reset the cursor.
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.
# File lib/mongo/cursor.rb, line 307 def to_a super end
# File lib/mongo/cursor.rb, line 644 def check_modifiable if @query_run || @closed raise InvalidOperation, "Cannot modify the query once it has been run or closed." end end
# File lib/mongo/cursor.rb, line 569 def checkin_socket(sock) if @checkin_read_pool @read_pool.checkin(sock) @checkin_read_pool = false elsif @checkin_connection if @command || @read_preference == :primary @connection.checkin_writer(sock) else @connection.checkin_reader(sock) end @checkin_connection = false end end
# File lib/mongo/cursor.rb, line 539 def checkout_socket_for_op_get_more if @read_pool && (@read_pool != @connection.read_pool) checkout_socket_from_read_pool else checkout_socket_from_connection end end
# File lib/mongo/cursor.rb, line 519 def checkout_socket_from_connection socket = nil begin @checkin_connection = true if @command || @read_preference == :primary socket = @connection.checkout_writer elsif @read_preference == :secondary_only socket = @connection.checkout_secondary else @read_pool = @connection.read_pool socket = @connection.checkout_reader end rescue SystemStackError, NoMemoryError, SystemCallError => ex @connection.close raise ex end socket end
# File lib/mongo/cursor.rb, line 547 def checkout_socket_from_read_pool new_pool = @connection.secondary_pools.detect do |pool| pool.host == @read_pool.host && pool.port == @read_pool.port end if new_pool sock = nil begin @read_pool = new_pool sock = new_pool.checkout @checkin_read_pool = true rescue SystemStackError, NoMemoryError, SystemCallError => ex @connection.close raise ex end return sock else raise Mongo::OperationFailure, "Failure to continue iterating " + "cursor because the the replica set member persisting this " + "cursor at #{@read_pool.host_string} cannot be found." end end
# File lib/mongo/cursor.rb, line 638 def close_cursor_if_query_complete if @limit > 0 && @returned >= @limit close end end
# File lib/mongo/cursor.rb, line 597 def construct_query_message message = BSON::ByteBuffer.new message.put_int(@options) BSON::BSON_RUBY.serialize_cstr(message, "#{@db.name}.#{@collection.name}") message.put_int(@skip) message.put_int(@limit) spec = query_contains_special_fields? ? construct_query_spec : @selector message.put_binary(BSON::BSON_CODER.serialize(spec, false).to_s) message.put_binary(BSON::BSON_CODER.serialize(@fields, false).to_s) if @fields message end
# File lib/mongo/cursor.rb, line 618 def construct_query_spec return @selector if @selector.has_key?('$query') spec = BSON::OrderedHash.new spec['$query'] = @selector spec['$orderby'] = Mongo::Support.format_order_clause(@order) if @order spec['$hint'] = @hint if @hint && @hint.length > 0 spec['$explain'] = true if @explain spec['$snapshot'] = true if @snapshot spec['$maxScan'] = @max_scan if @max_scan spec['$returnKey'] = true if @return_key spec['$showDiskLoc'] = true if @show_disk_loc spec end
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.
# File lib/mongo/cursor.rb, line 428 def convert_fields_for_query(fields) case fields when String, Symbol {fields => 1} when Array return nil if fields.length.zero? fields.each_with_object({}) { |field, hash| hash[field] = 1 } when Hash return fields end end
# File lib/mongo/cursor.rb, line 583 def force_checkin_socket(sock) if @checkin_read_pool @read_pool.checkin(sock) @checkin_read_pool = false else if @command || @read_preference == :primary @connection.checkin_writer(sock) else @connection.checkin_reader(sock) end @checkin_connection = false end end
# File lib/mongo/cursor.rb, line 609 def instrument_payload log = { :database => @db.name, :collection => @collection.name, :selector => selector } log[:fields] = @fields if @fields log[:skip] = @skip if @skip && (@skip != 0) log[:limit] = @limit if @limit && (@limit != 0) log[:order] = @order if @order log end
Return the number of documents remaining for this cursor.
# File lib/mongo/cursor.rb, line 441 def num_remaining if @cache.length == 0 if @query_run && (@options & OP_QUERY_EXHAUST != 0) close return 0 else refresh end end @cache.length end
Returns true if the query contains order, explain, hint, or snapshot.
# File lib/mongo/cursor.rb, line 633 def query_contains_special_fields? @order || @explain || @hint || @snapshot || @show_disk_loc || @max_scan || @return_key end
Refresh the documents in @cache. This means either sending the initial query or sending a GET_MORE operation.
# File lib/mongo/cursor.rb, line 456 def refresh if !@query_run send_initial_query elsif !@cursor_id.zero? send_get_more end end
# File lib/mongo/cursor.rb, line 484 def send_get_more message = BSON::ByteBuffer.new([0, 0, 0, 0]) # DB name. BSON::BSON_RUBY.serialize_cstr(message, "#{@db.name}.#{@collection.name}") # Number of results to return. if @limit > 0 limit = @limit - @returned if @batch_size > 0 limit = limit < @batch_size ? limit : @batch_size end message.put_int(limit) else message.put_int(@batch_size) end # Cursor id. message.put_long(@cursor_id) log(:debug, "cursor.refresh() for cursor #{@cursor_id}") if @logger sock = @socket || checkout_socket_for_op_get_more begin results, @n_received, @cursor_id = @connection.receive_message( Mongo::Constants::OP_GET_MORE, message, nil, sock, @command, nil) rescue ConnectionFailure, OperationFailure, OperationTimeout => ex force_checkin_socket(sock) raise ex end checkin_socket(sock) unless @socket @returned += @n_received @cache += results close_cursor_if_query_complete end
# File lib/mongo/cursor.rb, line 464 def send_initial_query message = construct_query_message sock = @socket || checkout_socket_from_connection instrument(:find, instrument_payload) do begin results, @n_received, @cursor_id = @connection.receive_message( Mongo::Constants::OP_QUERY, message, nil, sock, @command, nil, @options & OP_QUERY_EXHAUST != 0) rescue ConnectionFailure, OperationFailure, OperationTimeout => ex force_checkin_socket(sock) unless @socket raise ex end checkin_socket(sock) unless @socket @returned += @n_received @cache += results @query_run = true close_cursor_if_query_complete end end