Node.js MongoDB Driver API

Source: lib/cursor.js

  1. 'use strict';
  3. const Transform = require('stream').Transform;
  4. const PassThrough = require('stream').PassThrough;
  5. const deprecate = require('util').deprecate;
  6. const handleCallback = require('./utils').handleCallback;
  7. const ReadPreference = require('./core').ReadPreference;
  8. const MongoError = require('./core').MongoError;
  9. const CoreCursor = require('./core/cursor').CoreCursor;
  10. const CursorState = require('./core/cursor').CursorState;
  11. const Map = require('./core').BSON.Map;
  13. const each = require('./operations/cursor_ops').each;
  15. const CountOperation = require('./operations/count');
  16. const ExplainOperation = require('./operations/explain');
  17. const HasNextOperation = require('./operations/has_next');
  18. const NextOperation = require('./operations/next');
  19. const ToArrayOperation = require('./operations/to_array');
  21. const executeOperation = require('./operations/execute_operation');
  23. /**
  24.  * @fileOverview The **Cursor** class is an internal class that embodies a cursor on MongoDB
  25.  * allowing for iteration over the results returned from the underlying query. It supports
  26.  * one by one document iteration, conversion to an array or can be iterated as a Node 4.X
  27.  * or higher stream
  28.  *
  29.  * **CURSORS Cannot directly be instantiated**
  30.  * @example
  31.  * const MongoClient = require('mongodb').MongoClient;
  32.  * const test = require('assert');
  33.  * // Connection url
  34.  * const url = 'mongodb://localhost:27017';
  35.  * // Database Name
  36.  * const dbName = 'test';
  37.  * // Connect using MongoClient
  38.  * MongoClient.connect(url, function(err, client) {
  39.  *   // Create a collection we want to drop later
  40.  *   const col = client.db(dbName).collection('createIndexExample1');
  41.  *   // Insert a bunch of documents
  42.  *   col.insert([{a:1, b:1}
  43.  *     , {a:2, b:2}, {a:3, b:3}
  44.  *     , {a:4, b:4}], {w:1}, function(err, result) {
  45.  *     test.equal(null, err);
  46.  *     // Show that duplicate records got dropped
  47.  *     col.find({}).toArray(function(err, items) {
  48.  *       test.equal(null, err);
  49.  *       test.equal(4, items.length);
  50.  *       client.close();
  51.  *     });
  52.  *   });
  53.  * });
  54.  */
  56. /**
  57.  * Namespace provided by the code module
  58.  * @external CoreCursor
  59.  * @external Readable
  60.  */
  62. // Flags allowed for cursor
  63. const flags = ['tailable', 'oplogReplay', 'noCursorTimeout', 'awaitData', 'exhaust', 'partial'];
  64. const fields = ['numberOfRetries', 'tailableRetryInterval'];
  66. /**
  67.  * Creates a new Cursor instance (INTERNAL TYPE, do not instantiate directly)
  68.  * @class Cursor
  69.  * @extends external:CoreCursor
  70.  * @extends external:Readable
  71.  * @property {string} sortValue Cursor query sort setting.
  72.  * @property {boolean} timeout Is Cursor able to time out.
  73.  * @property {ReadPreference} readPreference Get cursor ReadPreference.
  74.  * @fires Cursor#data
  75.  * @fires Cursor#end
  76.  * @fires Cursor#close
  77.  * @fires Cursor#readable
  78.  * @return {Cursor} a Cursor instance.
  79.  * @example
  80.  * Cursor cursor options.
  81.  *
  82.  * collection.find({}).project({a:1})                             // Create a projection of field a
  83.  * collection.find({}).skip(1).limit(10)                          // Skip 1 and limit 10
  84.  * collection.find({}).batchSize(5)                               // Set batchSize on cursor to 5
  85.  * collection.find({}).filter({a:1})                              // Set query on the cursor
  86.  * collection.find({}).comment('add a comment')                   // Add a comment to the query, allowing to correlate queries
  87.  * collection.find({}).addCursorFlag('tailable', true)            // Set cursor as tailable
  88.  * collection.find({}).addCursorFlag('oplogReplay', true)         // Set cursor as oplogReplay
  89.  * collection.find({}).addCursorFlag('noCursorTimeout', true)     // Set cursor as noCursorTimeout
  90.  * collection.find({}).addCursorFlag('awaitData', true)           // Set cursor as awaitData
  91.  * collection.find({}).addCursorFlag('partial', true)             // Set cursor as partial
  92.  * collection.find({}).addQueryModifier('$orderby', {a:1})        // Set $orderby {a:1}
  93.  * collection.find({}).max(10)                                    // Set the cursor max
  94.  * collection.find({}).maxTimeMS(1000)                            // Set the cursor maxTimeMS
  95.  * collection.find({}).min(100)                                   // Set the cursor min
  96.  * collection.find({}).returnKey(true)                            // Set the cursor returnKey
  97.  * collection.find({}).setReadPreference(ReadPreference.PRIMARY)  // Set the cursor readPreference
  98.  * collection.find({}).showRecordId(true)                         // Set the cursor showRecordId
  99.  * collection.find({}).sort([['a', 1]])                           // Sets the sort order of the cursor query
  100.  * collection.find({}).hint('a_1')                                // Set the cursor hint
  101.  *
  102.  * All options are chainable, so one can do the following.
  103.  *
  104.  * collection.find({}).maxTimeMS(1000).maxScan(100).skip(1).toArray(..)
  105.  */
  106. class Cursor extends CoreCursor {
  107.   constructor(topology, ns, cmd, options) {
  108.     super(topology, ns, cmd, options);
  109.     if (this.operation) {
  110.       options = this.operation.options;
  111.     }
  113.     // Tailable cursor options
  114.     const numberOfRetries = options.numberOfRetries || 5;
  115.     const tailableRetryInterval = options.tailableRetryInterval || 500;
  116.     const currentNumberOfRetries = numberOfRetries;
  118.     // Get the promiseLibrary
  119.     const promiseLibrary = options.promiseLibrary || Promise;
  121.     // Internal cursor state
  122.     this.s = {
  123.       // Tailable cursor options
  124.       numberOfRetries: numberOfRetries,
  125.       tailableRetryInterval: tailableRetryInterval,
  126.       currentNumberOfRetries: currentNumberOfRetries,
  127.       // State
  128.       state: CursorState.INIT,
  129.       // Promise library
  130.       promiseLibrary,
  131.       // Current doc
  132.       currentDoc: null,
  133.       // explicitlyIgnoreSession
  134.       explicitlyIgnoreSession: !!options.explicitlyIgnoreSession
  135.     };
  137.     // Optional ClientSession
  138.     if (!options.explicitlyIgnoreSession && options.session) {
  139.       this.cursorState.session = options.session;
  140.     }
  142.     // Translate correctly
  143.     if (this.options.noCursorTimeout === true) {
  144.       this.addCursorFlag('noCursorTimeout', true);
  145.     }
  147.     // Get the batchSize
  148.     let batchSize = 1000;
  149.     if (this.cmd.cursor && this.cmd.cursor.batchSize) {
  150.       batchSize = this.cmd.cursor.batchSize;
  151.     } else if (options.cursor && options.cursor.batchSize) {
  152.       batchSize = options.cursor.batchSize;
  153.     } else if (typeof options.batchSize === 'number') {
  154.       batchSize = options.batchSize;
  155.     }
  157.     // Set the batchSize
  158.     this.setCursorBatchSize(batchSize);
  159.   }
  161.   get readPreference() {
  162.     if (this.operation) {
  163.       return this.operation.readPreference;
  164.     }
  166.     return this.options.readPreference;
  167.   }
  169.   get sortValue() {
  170.     return this.cmd.sort;
  171.   }
  173.   _initializeCursor(callback) {
  174.     if (this.operation && this.operation.session != null) {
  175.       this.cursorState.session = this.operation.session;
  176.     } else {
  177.       // implicitly create a session if one has not been provided
  178.       if (
  179.         !this.s.explicitlyIgnoreSession &&
  180.         !this.cursorState.session &&
  181.         this.topology.hasSessionSupport()
  182.       ) {
  183.         this.cursorState.session = this.topology.startSession({ owner: this });
  185.         if (this.operation) {
  186.           this.operation.session = this.cursorState.session;
  187.         }
  188.       }
  189.     }
  191.     super._initializeCursor(callback);
  192.   }
  194.   /**
  195.    * Check if there is any document still available in the cursor
  196.    * @method
  197.    * @param {Cursor~resultCallback} [callback] The result callback.
  198.    * @throws {MongoError}
  199.    * @return {Promise} returns Promise if no callback passed
  200.    */
  201.   hasNext(callback) {
  202.     const hasNextOperation = new HasNextOperation(this);
  204.     return executeOperation(this.topology, hasNextOperation, callback);
  205.   }
  207.   /**
  208.    * Get the next available document from the cursor, returns null if no more documents are available.
  209.    * @method
  210.    * @param {Cursor~resultCallback} [callback] The result callback.
  211.    * @throws {MongoError}
  212.    * @return {Promise} returns Promise if no callback passed
  213.    */
  214.   next(callback) {
  215.     const nextOperation = new NextOperation(this);
  217.     return executeOperation(this.topology, nextOperation, callback);
  218.   }
  220.   /**
  221.    * Set the cursor query
  222.    * @method
  223.    * @param {object} filter The filter object used for the cursor.
  224.    * @return {Cursor}
  225.    */
  226.   filter(filter) {
  227.     if (this.s.state === CursorState.CLOSED || this.s.state === CursorState.OPEN || this.isDead()) {
  228.       throw MongoError.create({ message: 'Cursor is closed', driver: true });
  229.     }
  231.     this.cmd.query = filter;
  232.     return this;
  233.   }
  235.   /**
  236.    * Set the cursor maxScan
  237.    * @method
  238.    * @param {object} maxScan Constrains the query to only scan the specified number of documents when fulfilling the query
  239.    * @deprecated as of MongoDB 4.0
  240.    * @return {Cursor}
  241.    */
  242.   maxScan(maxScan) {
  243.     if (this.s.state === CursorState.CLOSED || this.s.state === CursorState.OPEN || this.isDead()) {
  244.       throw MongoError.create({ message: 'Cursor is closed', driver: true });
  245.     }
  247.     this.cmd.maxScan = maxScan;
  248.     return this;
  249.   }
  251.   /**
  252.    * Set the cursor hint
  253.    * @method
  254.    * @param {object} hint If specified, then the query system will only consider plans using the hinted index.
  255.    * @return {Cursor}
  256.    */
  257.   hint(hint) {
  258.     if (this.s.state === CursorState.CLOSED || this.s.state === CursorState.OPEN || this.isDead()) {
  259.       throw MongoError.create({ message: 'Cursor is closed', driver: true });
  260.     }
  262.     this.cmd.hint = hint;
  263.     return this;
  264.   }
  266.   /**
  267.    * Set the cursor min
  268.    * @method
  269.    * @param {object} min Specify a $min value to specify the inclusive lower bound for a specific index in order to constrain the results of find(). The $min specifies the lower bound for all keys of a specific index in order.
  270.    * @return {Cursor}
  271.    */
  272.   min(min) {
  273.     if (this.s.state === CursorState.CLOSED || this.s.state === CursorState.OPEN || this.isDead()) {
  274.       throw MongoError.create({ message: 'Cursor is closed', driver: true });
  275.     }
  277.     this.cmd.min = min;
  278.     return this;
  279.   }
  281.   /**
  282.    * Set the cursor max
  283.    * @method
  284.    * @param {object} max Specify a $max value to specify the exclusive upper bound for a specific index in order to constrain the results of find(). The $max specifies the upper bound for all keys of a specific index in order.
  285.    * @return {Cursor}
  286.    */
  287.   max(max) {
  288.     if (this.s.state === CursorState.CLOSED || this.s.state === CursorState.OPEN || this.isDead()) {
  289.       throw MongoError.create({ message: 'Cursor is closed', driver: true });
  290.     }
  292.     this.cmd.max = max;
  293.     return this;
  294.   }
  296.   /**
  297.    * Set the cursor returnKey. If set to true, modifies the cursor to only return the index field or fields for the results of the query, rather than documents. If set to true and the query does not use an index to perform the read operation, the returned documents will not contain any fields.
  298.    * @method
  299.    * @param {bool} returnKey the returnKey value.
  300.    * @return {Cursor}
  301.    */
  302.   returnKey(value) {
  303.     if (this.s.state === CursorState.CLOSED || this.s.state === CursorState.OPEN || this.isDead()) {
  304.       throw MongoError.create({ message: 'Cursor is closed', driver: true });
  305.     }
  307.     this.cmd.returnKey = value;
  308.     return this;
  309.   }
  311.   /**
  312.    * Set the cursor showRecordId
  313.    * @method
  314.    * @param {object} showRecordId The $showDiskLoc option has now been deprecated and replaced with the showRecordId field. $showDiskLoc will still be accepted for OP_QUERY stye find.
  315.    * @return {Cursor}
  316.    */
  317.   showRecordId(value) {
  318.     if (this.s.state === CursorState.CLOSED || this.s.state === CursorState.OPEN || this.isDead()) {
  319.       throw MongoError.create({ message: 'Cursor is closed', driver: true });
  320.     }
  322.     this.cmd.showDiskLoc = value;
  323.     return this;
  324.   }
  326.   /**
  327.    * Set the cursor snapshot
  328.    * @method
  329.    * @param {object} snapshot The $snapshot operator prevents the cursor from returning a document more than once because an intervening write operation results in a move of the document.
  330.    * @deprecated as of MongoDB 4.0
  331.    * @return {Cursor}
  332.    */
  333.   snapshot(value) {
  334.     if (this.s.state === CursorState.CLOSED || this.s.state === CursorState.OPEN || this.isDead()) {
  335.       throw MongoError.create({ message: 'Cursor is closed', driver: true });
  336.     }
  338.     this.cmd.snapshot = value;
  339.     return this;
  340.   }
  342.   /**
  343.    * Set a node.js specific cursor option
  344.    * @method
  345.    * @param {string} field The cursor option to set ['numberOfRetries', 'tailableRetryInterval'].
  346.    * @param {object} value The field value.
  347.    * @throws {MongoError}
  348.    * @return {Cursor}
  349.    */
  350.   setCursorOption(field, value) {
  351.     if (this.s.state === CursorState.CLOSED || this.s.state === CursorState.OPEN || this.isDead()) {
  352.       throw MongoError.create({ message: 'Cursor is closed', driver: true });
  353.     }
  355.     if (fields.indexOf(field) === -1) {
  356.       throw MongoError.create({
  357.         message: `option ${field} is not a supported option ${fields}`,
  358.         driver: true
  359.       });
  360.     }
  362.     this.s[field] = value;
  363.     if (field === 'numberOfRetries') this.s.currentNumberOfRetries = value;
  364.     return this;
  365.   }
  367.   /**
  368.    * Add a cursor flag to the cursor
  369.    * @method
  370.    * @param {string} flag The flag to set, must be one of following ['tailable', 'oplogReplay', 'noCursorTimeout', 'awaitData', 'partial'].
  371.    * @param {boolean} value The flag boolean value.
  372.    * @throws {MongoError}
  373.    * @return {Cursor}
  374.    */
  375.   addCursorFlag(flag, value) {
  376.     if (this.s.state === CursorState.CLOSED || this.s.state === CursorState.OPEN || this.isDead()) {
  377.       throw MongoError.create({ message: 'Cursor is closed', driver: true });
  378.     }
  380.     if (flags.indexOf(flag) === -1) {
  381.       throw MongoError.create({
  382.         message: `flag ${flag} is not a supported flag ${flags}`,
  383.         driver: true
  384.       });
  385.     }
  387.     if (typeof value !== 'boolean') {
  388.       throw MongoError.create({ message: `flag ${flag} must be a boolean value`, driver: true });
  389.     }
  391.     this.cmd[flag] = value;
  392.     return this;
  393.   }
  395.   /**
  396.    * Add a query modifier to the cursor query
  397.    * @method
  398.    * @param {string} name The query modifier (must start with $, such as $orderby etc)
  399.    * @param {string|boolean|number} value The modifier value.
  400.    * @throws {MongoError}
  401.    * @return {Cursor}
  402.    */
  403.   addQueryModifier(name, value) {
  404.     if (this.s.state === CursorState.CLOSED || this.s.state === CursorState.OPEN || this.isDead()) {
  405.       throw MongoError.create({ message: 'Cursor is closed', driver: true });
  406.     }
  408.     if (name[0] !== '$') {
  409.       throw MongoError.create({ message: `${name} is not a valid query modifier`, driver: true });
  410.     }
  412.     // Strip of the $
  413.     const field = name.substr(1);
  414.     // Set on the command
  415.     this.cmd[field] = value;
  416.     // Deal with the special case for sort
  417.     if (field === 'orderby') this.cmd.sort = this.cmd[field];
  418.     return this;
  419.   }
  421.   /**
  422.    * Add a comment to the cursor query allowing for tracking the comment in the log.
  423.    * @method
  424.    * @param {string} value The comment attached to this query.
  425.    * @throws {MongoError}
  426.    * @return {Cursor}
  427.    */
  428.   comment(value) {
  429.     if (this.s.state === CursorState.CLOSED || this.s.state === CursorState.OPEN || this.isDead()) {
  430.       throw MongoError.create({ message: 'Cursor is closed', driver: true });
  431.     }
  433.     this.cmd.comment = value;
  434.     return this;
  435.   }
  437.   /**
  438.    * Set a maxAwaitTimeMS on a tailing cursor query to allow to customize the timeout value for the option awaitData (Only supported on MongoDB 3.2 or higher, ignored otherwise)
  439.    * @method
  440.    * @param {number} value Number of milliseconds to wait before aborting the tailed query.
  441.    * @throws {MongoError}
  442.    * @return {Cursor}
  443.    */
  444.   maxAwaitTimeMS(value) {
  445.     if (typeof value !== 'number') {
  446.       throw MongoError.create({ message: 'maxAwaitTimeMS must be a number', driver: true });
  447.     }
  449.     if (this.s.state === CursorState.CLOSED || this.s.state === CursorState.OPEN || this.isDead()) {
  450.       throw MongoError.create({ message: 'Cursor is closed', driver: true });
  451.     }
  453.     this.cmd.maxAwaitTimeMS = value;
  454.     return this;
  455.   }
  457.   /**
  458.    * Set a maxTimeMS on the cursor query, allowing for hard timeout limits on queries (Only supported on MongoDB 2.6 or higher)
  459.    * @method
  460.    * @param {number} value Number of milliseconds to wait before aborting the query.
  461.    * @throws {MongoError}
  462.    * @return {Cursor}
  463.    */
  464.   maxTimeMS(value) {
  465.     if (typeof value !== 'number') {
  466.       throw MongoError.create({ message: 'maxTimeMS must be a number', driver: true });
  467.     }
  469.     if (this.s.state === CursorState.CLOSED || this.s.state === CursorState.OPEN || this.isDead()) {
  470.       throw MongoError.create({ message: 'Cursor is closed', driver: true });
  471.     }
  473.     this.cmd.maxTimeMS = value;
  474.     return this;
  475.   }
  477.   /**
  478.    * Sets a field projection for the query.
  479.    * @method
  480.    * @param {object} value The field projection object.
  481.    * @throws {MongoError}
  482.    * @return {Cursor}
  483.    */
  484.   project(value) {
  485.     if (this.s.state === CursorState.CLOSED || this.s.state === CursorState.OPEN || this.isDead()) {
  486.       throw MongoError.create({ message: 'Cursor is closed', driver: true });
  487.     }
  489.     this.cmd.fields = value;
  490.     return this;
  491.   }
  493.   /**
  494.    * Sets the sort order of the cursor query.
  495.    * @method
  496.    * @param {(string|array|object)} keyOrList The key or keys set for the sort.
  497.    * @param {number} [direction] The direction of the sorting (1 or -1).
  498.    * @throws {MongoError}
  499.    * @return {Cursor}
  500.    */
  501.   sort(keyOrList, direction) {
  502.     if (this.options.tailable) {
  503.       throw MongoError.create({ message: "Tailable cursor doesn't support sorting", driver: true });
  504.     }
  506.     if (this.s.state === CursorState.CLOSED || this.s.state === CursorState.OPEN || this.isDead()) {
  507.       throw MongoError.create({ message: 'Cursor is closed', driver: true });
  508.     }
  510.     let order = keyOrList;
  512.     // We have an array of arrays, we need to preserve the order of the sort
  513.     // so we will us a Map
  514.     if (Array.isArray(order) && Array.isArray(order[0])) {
  515.       order = new Map(
  516.         order.map(x => {
  517.           const value = [x[0], null];
  518.           if (x[1] === 'asc') {
  519.             value[1] = 1;
  520.           } else if (x[1] === 'desc') {
  521.             value[1] = -1;
  522.           } else if (x[1] === 1 || x[1] === -1 || x[1].$meta) {
  523.             value[1] = x[1];
  524.           } else {
  525.             throw new MongoError(
  526.               "Illegal sort clause, must be of the form [['field1', '(ascending|descending)'], ['field2', '(ascending|descending)']]"
  527.             );
  528.           }
  530.           return value;
  531.         })
  532.       );
  533.     }
  535.     if (direction != null) {
  536.       order = [[keyOrList, direction]];
  537.     }
  539.     this.cmd.sort = order;
  540.     return this;
  541.   }
  543.   /**
  544.    * Set the batch size for the cursor.
  545.    * @method
  546.    * @param {number} value The number of documents to return per batch. See {@link https://www.mongodb.com/docs/manual/reference/command/find/|find command documentation}.
  547.    * @throws {MongoError}
  548.    * @return {Cursor}
  549.    */
  550.   batchSize(value) {
  551.     if (this.options.tailable) {
  552.       throw MongoError.create({
  553.         message: "Tailable cursor doesn't support batchSize",
  554.         driver: true
  555.       });
  556.     }
  558.     if (this.s.state === CursorState.CLOSED || this.isDead()) {
  559.       throw MongoError.create({ message: 'Cursor is closed', driver: true });
  560.     }
  562.     if (typeof value !== 'number') {
  563.       throw MongoError.create({ message: 'batchSize requires an integer', driver: true });
  564.     }
  566.     this.cmd.batchSize = value;
  567.     this.setCursorBatchSize(value);
  568.     return this;
  569.   }
  571.   /**
  572.    * Set the collation options for the cursor.
  573.    * @method
  574.    * @param {object} value The cursor collation options (MongoDB 3.4 or higher) settings for update operation (see 3.4 documentation for available fields).
  575.    * @throws {MongoError}
  576.    * @return {Cursor}
  577.    */
  578.   collation(value) {
  579.     this.cmd.collation = value;
  580.     return this;
  581.   }
  583.   /**
  584.    * Set the limit for the cursor.
  585.    * @method
  586.    * @param {number} value The limit for the cursor query.
  587.    * @throws {MongoError}
  588.    * @return {Cursor}
  589.    */
  590.   limit(value) {
  591.     if (this.options.tailable) {
  592.       throw MongoError.create({ message: "Tailable cursor doesn't support limit", driver: true });
  593.     }
  595.     if (this.s.state === CursorState.OPEN || this.s.state === CursorState.CLOSED || this.isDead()) {
  596.       throw MongoError.create({ message: 'Cursor is closed', driver: true });
  597.     }
  599.     if (typeof value !== 'number') {
  600.       throw MongoError.create({ message: 'limit requires an integer', driver: true });
  601.     }
  603.     this.cmd.limit = value;
  604.     this.setCursorLimit(value);
  605.     return this;
  606.   }
  608.   /**
  609.    * Set the skip for the cursor.
  610.    * @method
  611.    * @param {number} value The skip for the cursor query.
  612.    * @throws {MongoError}
  613.    * @return {Cursor}
  614.    */
  615.   skip(value) {
  616.     if (this.options.tailable) {
  617.       throw MongoError.create({ message: "Tailable cursor doesn't support skip", driver: true });
  618.     }
  620.     if (this.s.state === CursorState.OPEN || this.s.state === CursorState.CLOSED || this.isDead()) {
  621.       throw MongoError.create({ message: 'Cursor is closed', driver: true });
  622.     }
  624.     if (typeof value !== 'number') {
  625.       throw MongoError.create({ message: 'skip requires an integer', driver: true });
  626.     }
  628.     this.cmd.skip = value;
  629.     this.setCursorSkip(value);
  630.     return this;
  631.   }
  633.   /**
  634.    * The callback format for results
  635.    * @callback Cursor~resultCallback
  636.    * @param {MongoError} error An error instance representing the error during the execution.
  637.    * @param {(object|null|boolean)} result The result object if the command was executed successfully.
  638.    */
  640.   /**
  641.    * Clone the cursor
  642.    * @function external:CoreCursor#clone
  643.    * @return {Cursor}
  644.    */
  646.   /**
  647.    * Resets the cursor
  648.    * @function external:CoreCursor#rewind
  649.    * @return {null}
  650.    */
  652.   /**
  653.    * Iterates over all the documents for this cursor. As with **{cursor.toArray}**,
  654.    * not all of the elements will be iterated if this cursor had been previously accessed.
  655.    * In that case, **{cursor.rewind}** can be used to reset the cursor. However, unlike
  656.    * **{cursor.toArray}**, the cursor will only hold a maximum of batch size elements
  657.    * at any given time if batch size is specified. Otherwise, the caller is responsible
  658.    * for making sure that the entire result can fit the memory.
  659.    * @method
  660.    * @deprecated
  661.    * @param {Cursor~resultCallback} callback The result callback.
  662.    * @throws {MongoError}
  663.    * @return {null}
  664.    */
  665.   each(callback) {
  666.     // Rewind cursor state
  667.     this.rewind();
  668.     // Set current cursor to INIT
  669.     this.s.state = CursorState.INIT;
  670.     // Run the query
  671.     each(this, callback);
  672.   }
  674.   /**
  675.    * The callback format for the forEach iterator method
  676.    * @callback Cursor~iteratorCallback
  677.    * @param {Object} doc An emitted document for the iterator
  678.    */
  680.   /**
  681.    * The callback error format for the forEach iterator method
  682.    * @callback Cursor~endCallback
  683.    * @param {MongoError} error An error instance representing the error during the execution.
  684.    */
  686.   /**
  687.    * Iterates over all the documents for this cursor using the iterator, callback pattern.
  688.    * @method
  689.    * @param {Cursor~iteratorCallback} iterator The iteration callback.
  690.    * @param {Cursor~endCallback} callback The end callback.
  691.    * @throws {MongoError}
  692.    * @return {Promise} if no callback supplied
  693.    */
  694.   forEach(iterator, callback) {
  695.     // Rewind cursor state
  696.     this.rewind();
  698.     // Set current cursor to INIT
  699.     this.s.state = CursorState.INIT;
  701.     if (typeof callback === 'function') {
  702.       each(this, (err, doc) => {
  703.         if (err) {
  704.           callback(err);
  705.           return false;
  706.         }
  707.         if (doc != null) {
  708.           iterator(doc);
  709.           return true;
  710.         }
  711.         if (doc == null && callback) {
  712.           const internalCallback = callback;
  713.           callback = null;
  714.           internalCallback(null);
  715.           return false;
  716.         }
  717.       });
  718.     } else {
  719.       return new this.s.promiseLibrary((fulfill, reject) => {
  720.         each(this, (err, doc) => {
  721.           if (err) {
  722.             reject(err);
  723.             return false;
  724.           } else if (doc == null) {
  725.             fulfill(null);
  726.             return false;
  727.           } else {
  728.             iterator(doc);
  729.             return true;
  730.           }
  731.         });
  732.       });
  733.     }
  734.   }
  736.   /**
  737.    * Set the ReadPreference for the cursor.
  738.    * @method
  739.    * @param {(string|ReadPreference)} readPreference The new read preference for the cursor.
  740.    * @throws {MongoError}
  741.    * @return {Cursor}
  742.    */
  743.   setReadPreference(readPreference) {
  744.     if (this.s.state !== CursorState.INIT) {
  745.       throw MongoError.create({
  746.         message: 'cannot change cursor readPreference after cursor has been accessed',
  747.         driver: true
  748.       });
  749.     }
  751.     if (readPreference instanceof ReadPreference) {
  752.       this.options.readPreference = readPreference;
  753.     } else if (typeof readPreference === 'string') {
  754.       this.options.readPreference = new ReadPreference(readPreference);
  755.     } else {
  756.       throw new TypeError('Invalid read preference: ' + readPreference);
  757.     }
  759.     return this;
  760.   }
  762.   /**
  763.    * The callback format for results
  764.    * @callback Cursor~toArrayResultCallback
  765.    * @param {MongoError} error An error instance representing the error during the execution.
  766.    * @param {object[]} documents All the documents the satisfy the cursor.
  767.    */
  769.   /**
  770.    * Returns an array of documents. The caller is responsible for making sure that there
  771.    * is enough memory to store the results. Note that the array only contains partial
  772.    * results when this cursor had been previously accessed. In that case,
  773.    * cursor.rewind() can be used to reset the cursor.
  774.    * @method
  775.    * @param {Cursor~toArrayResultCallback} [callback] The result callback.
  776.    * @throws {MongoError}
  777.    * @return {Promise} returns Promise if no callback passed
  778.    */
  779.   toArray(callback) {
  780.     if (this.options.tailable) {
  781.       throw MongoError.create({
  782.         message: 'Tailable cursor cannot be converted to array',
  783.         driver: true
  784.       });
  785.     }
  787.     const toArrayOperation = new ToArrayOperation(this);
  789.     return executeOperation(this.topology, toArrayOperation, callback);
  790.   }
  792.   /**
  793.    * The callback format for results
  794.    * @callback Cursor~countResultCallback
  795.    * @param {MongoError} error An error instance representing the error during the execution.
  796.    * @param {number} count The count of documents.
  797.    */
  799.   /**
  800.    * Get the count of documents for this cursor
  801.    * @method
  802.    * @param {boolean} [applySkipLimit=true] Should the count command apply limit and skip settings on the cursor or in the passed in options.
  803.    * @param {object} [options] Optional settings.
  804.    * @param {number} [options.skip] The number of documents to skip.
  805.    * @param {number} [options.limit] The maximum amounts to count before aborting.
  806.    * @param {number} [options.maxTimeMS] Number of milliseconds to wait before aborting the query.
  807.    * @param {string} [options.hint] An index name hint for the query.
  808.    * @param {(ReadPreference|string)} [options.readPreference] The preferred read preference (ReadPreference.PRIMARY, ReadPreference.PRIMARY_PREFERRED, ReadPreference.SECONDARY, ReadPreference.SECONDARY_PREFERRED, ReadPreference.NEAREST).
  809.    * @param {Cursor~countResultCallback} [callback] The result callback.
  810.    * @return {Promise} returns Promise if no callback passed
  811.    */
  812.   count(applySkipLimit, opts, callback) {
  813.     if (this.cmd.query == null)
  814.       throw MongoError.create({
  815.         message: 'count can only be used with find command',
  816.         driver: true
  817.       });
  818.     if (typeof opts === 'function') (callback = opts), (opts = {});
  819.     opts = opts || {};
  821.     if (typeof applySkipLimit === 'function') {
  822.       callback = applySkipLimit;
  823.       applySkipLimit = true;
  824.     }
  826.     if (this.cursorState.session) {
  827.       opts = Object.assign({}, opts, { session: this.cursorState.session });
  828.     }
  830.     const countOperation = new CountOperation(this, applySkipLimit, opts);
  832.     return executeOperation(this.topology, countOperation, callback);
  833.   }
  835.   /**
  836.    * Close the cursor, sending a KillCursor command and emitting close.
  837.    * @method
  838.    * @param {object} [options] Optional settings.
  839.    * @param {boolean} [options.skipKillCursors] Bypass calling killCursors when closing the cursor.
  840.    * @param {Cursor~resultCallback} [callback] The result callback.
  841.    * @return {Promise} returns Promise if no callback passed
  842.    */
  843.   close(options, callback) {
  844.     if (typeof options === 'function') (callback = options), (options = {});
  845.     options = Object.assign({}, { skipKillCursors: false }, options);
  847.     this.s.state = CursorState.CLOSED;
  848.     if (!options.skipKillCursors) {
  849.       // Kill the cursor
  850.       this.kill();
  851.     }
  853.     const completeClose = () => {
  854.       // Emit the close event for the cursor
  855.       this.emit('close');
  857.       // Callback if provided
  858.       if (typeof callback === 'function') {
  859.         return handleCallback(callback, null, this);
  860.       }
  862.       // Return a Promise
  863.       return new this.s.promiseLibrary(resolve => {
  864.         resolve();
  865.       });
  866.     };
  868.     if (this.cursorState.session) {
  869.       if (typeof callback === 'function') {
  870.         return this._endSession(() => completeClose());
  871.       }
  873.       return new this.s.promiseLibrary(resolve => {
  874.         this._endSession(() => completeClose().then(resolve));
  875.       });
  876.     }
  878.     return completeClose();
  879.   }
  881.   /**
  882.    * Map all documents using the provided function
  883.    * @method
  884.    * @param {function} [transform] The mapping transformation method.
  885.    * @return {Cursor}
  886.    */
  887.   map(transform) {
  888.     if (this.cursorState.transforms && this.cursorState.transforms.doc) {
  889.       const oldTransform = this.cursorState.transforms.doc;
  890.       this.cursorState.transforms.doc = doc => {
  891.         return transform(oldTransform(doc));
  892.       };
  893.     } else {
  894.       this.cursorState.transforms = { doc: transform };
  895.     }
  897.     return this;
  898.   }
  900.   /**
  901.    * Is the cursor closed
  902.    * @method
  903.    * @return {boolean}
  904.    */
  905.   isClosed() {
  906.     return this.isDead();
  907.   }
  909.   destroy(err) {
  910.     if (err) this.emit('error', err);
  911.     this.pause();
  912.     this.close();
  913.   }
  915.   /**
  916.    * Return a modified Readable stream including a possible transform method.
  917.    * @method
  918.    * @param {object} [options] Optional settings.
  919.    * @param {function} [options.transform] A transformation method applied to each document emitted by the stream.
  920.    * @return {Cursor}
  921.    * TODO: replace this method with transformStream in next major release
  922.    */
  923.   stream(options) {
  924.     this.cursorState.streamOptions = options || {};
  925.     return this;
  926.   }
  928.   /**
  929.    * Return a modified Readable stream that applies a given transform function, if supplied. If none supplied,
  930.    * returns a stream of unmodified docs.
  931.    * @method
  932.    * @param {object} [options] Optional settings.
  933.    * @param {function} [options.transform] A transformation method applied to each document emitted by the stream.
  934.    * @return {stream}
  935.    */
  936.   transformStream(options) {
  937.     const streamOptions = options || {};
  938.     if (typeof streamOptions.transform === 'function') {
  939.       const stream = new Transform({
  940.         objectMode: true,
  941.         transform: function(chunk, encoding, callback) {
  942.           this.push(streamOptions.transform(chunk));
  943.           callback();
  944.         }
  945.       });
  947.       return this.pipe(stream);
  948.     }
  950.     return this.pipe(new PassThrough({ objectMode: true }));
  951.   }
  953.   /**
  954.    * Execute the explain for the cursor
  955.    * @method
  956.    * @param {Cursor~resultCallback} [callback] The result callback.
  957.    * @return {Promise} returns Promise if no callback passed
  958.    */
  959.   explain(callback) {
  960.     // NOTE: the next line includes a special case for operations which do not
  961.     //       subclass `CommandOperationV2`. To be removed asap.
  962.     if (this.operation && this.operation.cmd == null) {
  963.       this.operation.options.explain = true;
  964.       this.operation.fullResponse = false;
  965.       return executeOperation(this.topology, this.operation, callback);
  966.     }
  968.     this.cmd.explain = true;
  970.     // Do we have a readConcern
  971.     if (this.cmd.readConcern) {
  972.       delete this.cmd['readConcern'];
  973.     }
  975.     const explainOperation = new ExplainOperation(this);
  977.     return executeOperation(this.topology, explainOperation, callback);
  978.   }
  980.   /**
  981.    * Return the cursor logger
  982.    * @method
  983.    * @return {Logger} return the cursor logger
  984.    * @ignore
  985.    */
  986.   getLogger() {
  987.     return this.logger;
  988.   }
  989. }
  991. /**
  992.  * Cursor stream data event, fired for each document in the cursor.
  993.  *
  994.  * @event Cursor#data
  995.  * @type {object}
  996.  */
  998. /**
  999.  * Cursor stream end event
  1000.  *
  1001.  * @event Cursor#end
  1002.  * @type {null}
  1003.  */
  1005. /**
  1006.  * Cursor stream close event
  1007.  *
  1008.  * @event Cursor#close
  1009.  * @type {null}
  1010.  */
  1012. /**
  1013.  * Cursor stream readable event
  1014.  *
  1015.  * @event Cursor#readable
  1016.  * @type {null}
  1017.  */
  1019. // aliases
  1020. Cursor.prototype.maxTimeMs = Cursor.prototype.maxTimeMS;
  1022. // deprecated methods
  1023. deprecate(Cursor.prototype.each, 'Cursor.each is deprecated. Use Cursor.forEach instead.');
  1024. deprecate(
  1025.   Cursor.prototype.maxScan,
  1026.   'Cursor.maxScan is deprecated, and will be removed in a later version'
  1027. );
  1029. deprecate(
  1030.   Cursor.prototype.snapshot,
  1031.   'Cursor Snapshot is deprecated, and will be removed in a later version'
  1032. );
  1034. /**
  1035.  * The read() method pulls some data out of the internal buffer and returns it. If there is no data available, then it will return null.
  1036.  * @function external:Readable#read
  1037.  * @param {number} size Optional argument to specify how much data to read.
  1038.  * @return {(String | Buffer | null)}
  1039.  */
  1041. /**
  1042.  * Call this function to cause the stream to return strings of the specified encoding instead of Buffer objects.
  1043.  * @function external:Readable#setEncoding
  1044.  * @param {string} encoding The encoding to use.
  1045.  * @return {null}
  1046.  */
  1048. /**
  1049.  * This method will cause the readable stream to resume emitting data events.
  1050.  * @function external:Readable#resume
  1051.  * @return {null}
  1052.  */
  1054. /**
  1055.  * This method will cause a stream in flowing-mode to stop emitting data events. Any data that becomes available will remain in the internal buffer.
  1056.  * @function external:Readable#pause
  1057.  * @return {null}
  1058.  */
  1060. /**
  1061.  * This method pulls all the data out of a readable stream, and writes it to the supplied destination, automatically managing the flow so that the destination is not overwhelmed by a fast readable stream.
  1062.  * @function external:Readable#pipe
  1063.  * @param {Writable} destination The destination for writing data
  1064.  * @param {object} [options] Pipe options
  1065.  * @return {null}
  1066.  */
  1068. /**
  1069.  * This method will remove the hooks set up for a previous pipe() call.
  1070.  * @function external:Readable#unpipe
  1071.  * @param {Writable} [destination] The destination for writing data
  1072.  * @return {null}
  1073.  */
  1075. /**
  1076.  * This is useful in certain cases where a stream is being consumed by a parser, which needs to "un-consume" some data that it has optimistically pulled out of the source, so that the stream can be passed on to some other party.
  1077.  * @function external:Readable#unshift
  1078.  * @param {(Buffer|string)} chunk Chunk of data to unshift onto the read queue.
  1079.  * @return {null}
  1080.  */
  1082. /**
  1083.  * Versions of Node prior to v0.10 had streams that did not implement the entire Streams API as it is today. (See "Compatibility" below for more information.)
  1084.  * @function external:Readable#wrap
  1085.  * @param {Stream} stream An "old style" readable stream.
  1086.  * @return {null}
  1087.  */
  1089. module.exports = Cursor;