Class Mongo::Cursor
In: lib/mongo/cursor.rb
Parent: Object

A cursor over query results. Returned objects are hashes.

Methods

add_option   alive?   batch_size   close   closed?   count   each   explain   has_next?   inspect   limit   new   next   next_document   query_options_hash   query_opts   remove_option   rewind!   skip   sort   to_a  

Included Modules

Enumerable Mongo::Constants Mongo::Conversions Mongo::Logging

Attributes

collection  [R] 
cursor_id  [R] 
fields  [R] 
full_collection_name  [R] 
hint  [R] 
options  [R] 
order  [R] 
selector  [R] 
show_disk_loc  [R] 
snapshot  [R] 
timeout  [R] 
transformer  [R] 

Public Class methods

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

[Source]

# File lib/mongo/cursor.rb, line 39
    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

Public Instance methods

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

[Source]

# 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 Cursor#next.

@return [Boolean]

[Source]

# File lib/mongo/cursor.rb, line 115
    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.

@param [Integer] size either 0 or some integer greater than 1. If 0,

  the server will determine the batch size.

@return [Cursor]

[Source]

# 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: Collection#find takes an optional block argument which can be used to ensure that your cursors get closed.

@return [True]

[Source]

# 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]

[Source]

# 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.

[Source]

# File lib/mongo/cursor.rb, line 181
    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

[Source]

# 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

[Source]

# 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]

[Source]

# File lib/mongo/cursor.rb, line 170
    def has_next?
      num_remaining > 0
    end

Clean output for inspect.

[Source]

# 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 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

[Source]

# File lib/mongo/cursor.rb, line 232
    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.

[Source]

# File lib/mongo/cursor.rb, line 122
    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
next_document()

Alias for next

Get the query options for this Cursor.

@return [Hash]

[Source]

# 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.

[Source]

# 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

[Source]

# 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.

[Source]

# File lib/mongo/cursor.rb, line 157
    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 Collection#find method, and only the last skip applied has an effect.

@return [Integer]

@raise [InvalidOperation] if this cursor has already been used.

[Source]

# File lib/mongo/cursor.rb, line 249
    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 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.

[Source]

# File lib/mongo/cursor.rb, line 209
    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

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 Cursor#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.

[Source]

# File lib/mongo/cursor.rb, line 307
    def to_a
      super
    end

[Validate]