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+/*!
+ * Module dependencies.
+ */
+
+var PromiseProvider = require('./promise_provider');
+var Readable = require('stream').Readable;
+var helpers = require('./queryhelpers');
+var util = require('util');
+
+/**
+ * A QueryCursor is a concurrency primitive for processing query results
+ * one document at a time. A QueryCursor fulfills the [Node.js streams3 API](https://strongloop.com/strongblog/whats-new-io-js-beta-streams3/),
+ * in addition to several other mechanisms for loading documents from MongoDB
+ * one at a time.
+ *
+ * Unless you're an advanced user, do **not** instantiate this class directly.
+ * Use [`Query#cursor()`](/docs/api.html#query_Query-cursor) instead.
+ *
+ * @param {Query} query
+ * @param {Object} options query options passed to `.find()`
+ * @inherits Readable
+ * @event `cursor`: Emitted when the cursor is created
+ * @event `error`: Emitted when an error occurred
+ * @event `data`: Emitted when the stream is flowing and the next doc is ready
+ * @event `end`: Emitted when the stream is exhausted
+ * @api public
+ */
+
+function QueryCursor(query, options) {
+ Readable.call(this, { objectMode: true });
+
+ this.cursor = null;
+ this.query = query;
+ this._transforms = options.transform ? [options.transform] : [];
+ var _this = this;
+ var model = query.model;
+ model.collection.find(query._conditions, options, function(err, cursor) {
+ if (_this._error) {
+ cursor.close(function() {});
+ _this.listeners('error').length > 0 && _this.emit('error', _this._error);
+ }
+ if (err) {
+ return _this.emit('error', err);
+ }
+ _this.cursor = cursor;
+ _this.emit('cursor', cursor);
+ });
+}
+
+util.inherits(QueryCursor, Readable);
+
+/*!
+ * Necessary to satisfy the Readable API
+ */
+
+QueryCursor.prototype._read = function() {
+ var _this = this;
+ _next(this, function(error, doc) {
+ if (error) {
+ return _this.emit('error', error);
+ }
+ if (!doc) {
+ _this.push(null);
+ return _this.cursor.close(function(error) {
+ if (error) {
+ return _this.emit('error', error);
+ }
+ _this.emit('close');
+ });
+ }
+ _this.push(doc);
+ });
+};
+
+/**
+ * Registers a transform function which subsequently maps documents retrieved
+ * via the streams interface or `.next()`
+ *
+ * ####Example
+ *
+ * // Map documents returned by `data` events
+ * Thing.
+ * find({ name: /^hello/ }).
+ * cursor().
+ * map(function (doc) {
+ * doc.foo = "bar";
+ * return doc;
+ * })
+ * on('data', function(doc) { console.log(doc.foo); });
+ *
+ * // Or map documents returned by `.next()`
+ * var cursor = Thing.find({ name: /^hello/ }).
+ * cursor().
+ * map(function (doc) {
+ * doc.foo = "bar";
+ * return doc;
+ * });
+ * cursor.next(function(error, doc) {
+ * console.log(doc.foo);
+ * });
+ *
+ * @param {Function} fn
+ * @return {QueryCursor}
+ * @api public
+ * @method map
+ */
+
+QueryCursor.prototype.map = function(fn) {
+ this._transforms.push(fn);
+ return this;
+};
+
+/*!
+ * Marks this cursor as errored
+ */
+
+QueryCursor.prototype._markError = function(error) {
+ this._error = error;
+ return this;
+};
+
+/**
+ * Marks this cursor as closed. Will stop streaming and subsequent calls to
+ * `next()` will error.
+ *
+ * @param {Function} callback
+ * @return {Promise}
+ * @api public
+ * @method close
+ * @emits close
+ * @see MongoDB driver cursor#close http://mongodb.github.io/node-mongodb-native/2.1/api/Cursor.html#close
+ */
+
+QueryCursor.prototype.close = function(callback) {
+ var Promise = PromiseProvider.get();
+ var _this = this;
+ return new Promise.ES6(function(resolve, reject) {
+ _this.cursor.close(function(error) {
+ if (error) {
+ callback && callback(error);
+ reject(error);
+ return _this.listeners('error').length > 0 &&
+ _this.emit('error', error);
+ }
+ _this.emit('close');
+ resolve();
+ callback && callback();
+ });
+ });
+};
+
+/**
+ * Get the next document from this cursor. Will return `null` when there are
+ * no documents left.
+ *
+ * @param {Function} callback
+ * @return {Promise}
+ * @api public
+ * @method next
+ */
+
+QueryCursor.prototype.next = function(callback) {
+ var Promise = PromiseProvider.get();
+ var _this = this;
+ return new Promise.ES6(function(resolve, reject) {
+ _next(_this, function(error, doc) {
+ if (error) {
+ callback && callback(error);
+ return reject(error);
+ }
+ callback && callback(null, doc);
+ resolve(doc);
+ });
+ });
+};
+
+/**
+ * Execute `fn` for every document in the cursor. If `fn` returns a promise,
+ * will wait for the promise to resolve before iterating on to the next one.
+ * Returns a promise that resolves when done.
+ *
+ * @param {Function} fn
+ * @param {Function} [callback] executed when all docs have been processed
+ * @return {Promise}
+ * @api public
+ * @method eachAsync
+ */
+
+QueryCursor.prototype.eachAsync = function(fn, callback) {
+ var Promise = PromiseProvider.get();
+ var _this = this;
+
+ var handleNextResult = function(doc, callback) {
+ var promise = fn(doc);
+ if (promise && typeof promise.then === 'function') {
+ promise.then(
+ function() { callback(null); },
+ function(error) { callback(error); });
+ } else {
+ callback(null);
+ }
+ };
+
+ var iterate = function(callback) {
+ return _next(_this, function(error, doc) {
+ if (error) {
+ return callback(error);
+ }
+ if (!doc) {
+ return callback(null);
+ }
+ handleNextResult(doc, function(error) {
+ if (error) {
+ return callback(error);
+ }
+ // Make sure to clear the stack re: gh-4697
+ setTimeout(function() {
+ iterate(callback);
+ }, 0);
+ });
+ });
+ };
+
+ return new Promise.ES6(function(resolve, reject) {
+ iterate(function(error) {
+ if (error) {
+ callback && callback(error);
+ return reject(error);
+ }
+ callback && callback(null);
+ return resolve();
+ });
+ });
+};
+
+/*!
+ * Get the next doc from the underlying cursor and mongooseify it
+ * (populate, etc.)
+ */
+
+function _next(ctx, cb) {
+ var callback = cb;
+ if (ctx._transforms.length) {
+ callback = function(err, doc) {
+ if (err || doc === null) return cb(err, doc);
+ cb(err, ctx._transforms.reduce(function(doc, fn) {
+ return fn(doc);
+ }, doc));
+ };
+ }
+
+ if (ctx._error) {
+ return process.nextTick(function() {
+ callback(ctx._error);
+ });
+ }
+
+ if (ctx.cursor) {
+ ctx.cursor.next(function(error, doc) {
+ if (error) {
+ return callback(error);
+ }
+ if (!doc) {
+ return callback(null, null);
+ }
+
+ var opts = ctx.query._mongooseOptions;
+ if (!opts.populate) {
+ return opts.lean === true ?
+ callback(null, doc) :
+ _create(ctx, doc, null, callback);
+ }
+
+ var pop = helpers.preparePopulationOptionsMQ(ctx.query,
+ ctx.query._mongooseOptions);
+ pop.forEach(function(option) {
+ delete option.model;
+ });
+ pop.__noPromise = true;
+ ctx.query.model.populate(doc, pop, function(err, doc) {
+ if (err) {
+ return callback(err);
+ }
+ return opts.lean === true ?
+ callback(null, doc) :
+ _create(ctx, doc, pop, callback);
+ });
+ });
+ } else {
+ ctx.once('cursor', function() {
+ _next(ctx, callback);
+ });
+ }
+}
+
+/*!
+ * Convert a raw doc into a full mongoose doc.
+ */
+
+function _create(ctx, doc, populatedIds, cb) {
+ var instance = helpers.createModel(ctx.query.model, doc, ctx.query._fields);
+ var opts = populatedIds ?
+ { populated: populatedIds } :
+ undefined;
+
+ instance.init(doc, opts, function(err) {
+ if (err) {
+ return cb(err);
+ }
+ cb(null, instance);
+ });
+}
+
+module.exports = QueryCursor;