class Mongo::Cursor
Client-side representation of an iterator over a query result set on the server.
Cursor
objects are not directly exposed to application code. Rather, Collection::View
exposes the Enumerable
interface to the applications, and the enumerator is backed by a Cursor
instance.
@example Get an array of 5 users named Emily.
users.find({:name => 'Emily'}).limit(5).to_a
@example Call a block on each user doc.
users.find.each { |doc| puts doc }
@api private
Attributes
@api private
The resume token tracked by the cursor for change stream resuming
@return [ BSON::Document | nil ] The cursor resume token. @api private
@api private
@return [ Collection::View
] view The collection view.
Public Class Methods
Finalize the cursor for garbage collection. Schedules this cursor to be included in a killCursors operation executed by the Cluster's CursorReaper.
@param [ Cursor::KillSpec
] kill_spec
The KillCursor operation specification. @param [ Mongo::Cluster
] cluster The cluster associated with this cursor and its server.
@return [ Proc ] The Finalizer.
@api private
# File lib/mongo/cursor.rb, line 110 def self.finalize(kill_spec, cluster) unless KillSpec === kill_spec raise ArgumentError, "First argument must be a KillSpec: #{kill_spec.inspect}" end proc do cluster.schedule_kill_cursor(kill_spec) end end
Creates a Cursor
object.
@example Instantiate the cursor.
Mongo::Cursor.new(view, response, server)
@param [ CollectionView ] view The CollectionView
defining the query. @param [ Operation::Result
] result The result of the first execution. @param [ Server
] server The server this cursor is locked to. @param [ Hash ] options The cursor options.
@option options [ true, false ] :disable_retry Whether to disable
retrying on error when sending getMore operations (deprecated, getMore operations are no longer retried)
@option options [ true, false ] :retry_reads Retry reads (following
the modern mechanism), default is true
@since 2.0.0
# File lib/mongo/cursor.rb, line 69 def initialize(view, result, server, options = {}) unless result.is_a?(Operation::Result) raise ArgumentError, "Second argument must be a Mongo::Operation::Result: #{result.inspect}" end @view = view @server = server @initial_result = result @namespace = result.namespace @remaining = limit if limited? set_cursor_id(result) if @cursor_id.nil? raise ArgumentError, 'Cursor id must be present in the result' end @connection_global_id = result.connection_global_id @options = options @session = @options[:session] @explicitly_closed = false @lock = Mutex.new unless closed? register ObjectSpace.define_finalizer(self, self.class.finalize(kill_spec(@connection_global_id), cluster)) end end
Public Instance Methods
Get the batch size.
@example Get the batch size.
cursor.batch_size
@return [ Integer ] The batch size.
@since 2.2.0
# File lib/mongo/cursor.rb, line 261 def batch_size value = @view.batch_size && @view.batch_size > 0 ? @view.batch_size : limit if value == 0 nil else value end end
Closes this cursor, freeing any associated resources on the client and the server.
@return [ nil ] Always nil.
# File lib/mongo/cursor.rb, line 287 def close return if closed? unregister read_with_one_retry do spec = { coll_name: collection_name, db_name: database.name, cursor_ids: [id], } op = Operation::KillCursors.new(spec) execute_operation(op) end nil rescue Error::OperationFailure, Error::SocketError, Error::SocketTimeoutError, Error::ServerNotUsable # Errors are swallowed since there is noting can be done by handling them. ensure end_session @cursor_id = 0 @lock.synchronize do @explicitly_closed = true end end
Is the cursor closed?
@example Is the cursor closed?
cursor.closed?
@return [ true, false ] If the cursor is closed.
@since 2.2.0
# File lib/mongo/cursor.rb, line 278 def closed? # @cursor_id should in principle never be nil @cursor_id.nil? || @cursor_id == 0 end
Get the parsed collection name.
@example Get the parsed collection name.
cursor.coll_name
@return [ String ] The collection name.
@since 2.2.0
# File lib/mongo/cursor.rb, line 320 def collection_name # In most cases, this will be equivalent to the name of the collection # object in the driver. However, in some cases (e.g. when connected # to an Atlas Data Lake), the namespace returned by the find command # may be different, which is why we want to use the collection name based # on the namespace in the command result. if @namespace # Often, the namespace will be in the format "database.collection". # However, sometimes the collection name will contain periods, which # is why this method joins all the namespace components after the first. ns_components = @namespace.split('.') ns_components[1...ns_components.length].join('.') else collection.name end end
Iterate through documents returned from the query.
A cursor may be iterated at most once. Incomplete iteration is also allowed. Attempting to iterate the cursor more than once raises InvalidCursorOperation.
@example Iterate over the documents in the cursor.
cursor.each do |doc| ... end
@return [ Enumerator ] The enumerator.
@since 2.0.0
# File lib/mongo/cursor.rb, line 145 def each # If we already iterated past the first batch (i.e., called get_more # at least once), the cursor on the server side has advanced past # the first batch and restarting iteration from the beginning by # returning initial result would miss documents in the second batch # and subsequent batches up to wherever the cursor is. Detect this # condition and abort the iteration. # # In a future driver version, each would either continue from the # end of previous iteration or would always restart from the # beginning. if @get_more_called raise Error::InvalidCursorOperation, 'Cannot restart iteration of a cursor which issued a getMore' end # To maintain compatibility with pre-2.10 driver versions, reset # the documents array each time a new iteration is started. @documents = nil if block_given? # StopIteration raised by try_next ends this loop. loop do document = try_next if explicitly_closed? raise Error::InvalidCursorOperation, 'Cursor was explicitly closed' end yield document if document end self else documents = [] # StopIteration raised by try_next ends this loop. loop do document = try_next if explicitly_closed? raise Error::InvalidCursorOperation, 'Cursor was explicitly closed' end documents << document if document end documents end end
@api private
# File lib/mongo/cursor.rb, line 394 def fully_iterated? !!@fully_iterated end
Execute a getMore command and return the batch of documents obtained from the server.
@return [ Array<BSON::Document> ] The batch of documents
@api private
# File lib/mongo/cursor.rb, line 370 def get_more @get_more_called = true # Modern retryable reads specification prohibits retrying getMores. # Legacy retryable read logic used to retry getMores, but since # doing so may result in silent data loss, the driver no longer retries # getMore operations in any circumstance. # https://github.com/mongodb/specifications/blob/master/source/retryable-reads/retryable-reads.rst#qa process(execute_operation(get_more_operation)) end
Get the cursor id.
@example Get the cursor id.
cursor.id
@note A cursor id of 0 means the cursor was closed on the server.
@return [ Integer ] The cursor id.
@since 2.2.0
# File lib/mongo/cursor.rb, line 347 def id @cursor_id end
Get a human-readable string representation of Cursor
.
@example Inspect the cursor.
cursor.inspect
@return [ String ] A string representation of a Cursor
instance.
@since 2.0.0
# File lib/mongo/cursor.rb, line 127 def inspect "#<Mongo::Cursor:0x#{object_id} @view=#{@view.inspect}>" end
@api private
# File lib/mongo/cursor.rb, line 382 def kill_spec(connection_global_id) KillSpec.new( cursor_id: id, coll_name: collection_name, db_name: database.name, connection_global_id: connection_global_id, server_address: server.address, session: @session, ) end
Get the number of documents to return. Used on 3.0 and lower server versions.
@example Get the number to return.
cursor.to_return
@return [ Integer ] The number of documents to return.
@since 2.2.0
# File lib/mongo/cursor.rb, line 360 def to_return use_limit? ? @remaining : (batch_size || 0) end
Return one document from the query, if one is available.
This method will wait up to max_await_time_ms milliseconds for changes from the server, and if no changes are received it will return nil. If there are no more documents to return from the server, or if we have exhausted the cursor, it will raise a StopIteration exception.
@note This method is experimental and subject to change.
@return [ BSON::Document | nil ] A document.
@raise [ StopIteration ] Raised on the calls after the cursor had been
completely iterated.
@api private
# File lib/mongo/cursor.rb, line 205 def try_next if @documents.nil? # Since published versions of Mongoid have a copy of old driver cursor # code, our dup call in #process isn't invoked when Mongoid query # cache is active. Work around that by also calling dup here on # the result of #process which might come out of Mongoid's code. @documents = process(@initial_result).dup # the documents here can be an empty array, hence # we may end up issuing a getMore in the first try_next call end if @documents.empty? # On empty batches, we cache the batch resume token cache_batch_resume_token unless closed? if exhausted? close @fully_iterated = true raise StopIteration end @documents = get_more else @fully_iterated = true raise StopIteration end else # cursor is closed here # keep documents as an empty array end # If there is at least one document, cache its _id if @documents[0] cache_resume_token(@documents[0]) end # Cache the batch resume token if we are iterating # over the last document, or if the batch is empty if @documents.size <= 1 cache_batch_resume_token if closed? @fully_iterated = true end end return @documents.shift end
Private Instance Methods
# File lib/mongo/cursor.rb, line 406 def batch_size_for_get_more if batch_size && use_limit? [batch_size, @remaining].min else batch_size end end
# File lib/mongo/cursor.rb, line 424 def cache_batch_resume_token @resume_token = @post_batch_resume_token if @post_batch_resume_token end
# File lib/mongo/cursor.rb, line 418 def cache_resume_token(doc) if doc[:_id] && doc[:_id].is_a?(Hash) @resume_token = doc[:_id] && doc[:_id].dup.freeze end end
# File lib/mongo/cursor.rb, line 453 def end_session @session.end_session if @session && @session.implicit? end
# File lib/mongo/cursor.rb, line 498 def execute_operation(op) context = Operation::Context.new( client: client, session: @session, connection_global_id: @connection_global_id, ) op.execute(@server, context: context) end
# File lib/mongo/cursor.rb, line 414 def exhausted? limited? ? @remaining <= 0 : false end
# File lib/mongo/cursor.rb, line 400 def explicitly_closed? @lock.synchronize do @explicitly_closed end end
# File lib/mongo/cursor.rb, line 428 def get_more_operation spec = { session: @session, db_name: database.name, coll_name: collection_name, cursor_id: id, # 3.2+ servers use batch_size, 3.0- servers use to_return. # TODO should to_return be calculated in the operation layer? batch_size: batch_size_for_get_more, to_return: to_return, max_time_ms: if view.respond_to?(:max_await_time_ms) && view.max_await_time_ms && view.options[:await_data] then view.max_await_time_ms else nil end, } if view.respond_to?(:options) && view.options.is_a?(Hash) spec[:comment] = view.options[:comment] unless view.options[:comment].nil? end Operation::GetMore.new(spec) end
# File lib/mongo/cursor.rb, line 486 def limit @view.send(:limit) end
# File lib/mongo/cursor.rb, line 457 def limited? limit ? limit > 0 : false end
# File lib/mongo/cursor.rb, line 461 def process(result) @remaining -= result.returned_count if limited? # #process is called for the first batch of results. In this case # the @cursor_id may be zero (all results fit in the first batch). # Thus we need to check both @cursor_id and the cursor_id of the result # prior to calling unregister here. unregister if !closed? && result.cursor_id == 0 @cursor_id = set_cursor_id(result) if result.respond_to?(:post_batch_resume_token) @post_batch_resume_token = result.post_batch_resume_token end end_session if closed? # Since our iteration code mutates the documents array by calling #shift # on it, duplicate the documents here to permit restarting iteration # from the beginning of the cursor as long as get_more was not called result.documents.dup end
# File lib/mongo/cursor.rb, line 490 def register cluster.register_cursor(@cursor_id) end
Sets @cursor_id from the operation result.
In the operation result cursor id can be represented either as Integer value or as BSON::Int64. This method ensures that the instance variable is always of type Integer.
@param [ Operation::Result
] result The result of the operation.
@api private
# File lib/mongo/cursor.rb, line 516 def set_cursor_id(result) @cursor_id = if result.cursor_id.is_a?(BSON::Int64) result.cursor_id.value else result.cursor_id end end
# File lib/mongo/cursor.rb, line 494 def unregister cluster.unregister_cursor(@cursor_id) end
# File lib/mongo/cursor.rb, line 482 def use_limit? limited? && batch_size >= @remaining end