# object.js

    const _ = require('underscore');
    const AVError = require('./error');
    const AVRequest = require('./request').request;
    const utils = require('./utils');

    const RESERVED_KEYS = ['objectId', 'createdAt', 'updatedAt'];
    const checkReservedKey = key => {
      if (RESERVED_KEYS.indexOf(key) !== -1) {
        throw new Error(`key[${key}] is reserved`);
      }
    };

    // AV.Object is analogous to the Java AVObject.
    // It also implements the same interface as a Backbone model.

    module.exports = function(AV) {
      /**
       * Creates a new model with defined attributes. A client id (cid) is
       * automatically generated and assigned for you.
       *
       * <p>You won't normally call this method directly.  It is recommended that
       * you use a subclass of <code>AV.Object</code> instead, created by calling
       * <code>extend</code>.</p>
       *
       * <p>However, if you don't want to use a subclass, or aren't sure which
       * subclass is appropriate, you can use this form:<pre>
       *     var object = new AV.Object("ClassName");
       * </pre>
       * That is basically equivalent to:<pre>
       *     var MyClass = AV.Object.extend("ClassName");
       *     var object = new MyClass();
       * </pre></p>
       *
       * @param {Object} attributes The initial set of data to store in the object.
       * @param {Object} options A set of Backbone-like options for creating the
       *     object.  The only option currently supported is "collection".
       * @see AV.Object.extend
       *
       * @class
       *
       * <p>The fundamental unit of AV data, which implements the Backbone Model
       * interface.</p>
       */
      AV.Object = function(attributes, options) {
        // Allow new AV.Object("ClassName") as a shortcut to _create.
        if (_.isString(attributes)) {
          return AV.Object._create.apply(this, arguments);
        }

        attributes = attributes || {};
        if (options && options.parse) {
          attributes = this.parse(attributes);
          attributes = this._mergeMagicFields(attributes);
        }
        var defaults = AV._getValue(this, 'defaults');
        if (defaults) {
          attributes = _.extend({}, defaults, attributes);
        }
        if (options && options.collection) {
          this.collection = options.collection;
        }

        this._serverData = {};  // The last known data for this object from cloud.
        this._opSetQueue = [{}];  // List of sets of changes to the data.
        this._flags = {};
        this.attributes = {};  // The best estimate of this's current data.

        this._hashedJSON = {};  // Hash of values of containers at last save.
        this._escapedAttributes = {};
        this.cid = _.uniqueId('c');
        this.changed = {};
        this._silent = {};
        this._pending = {};
        this.set(attributes, { silent: true });
        this.changed = {};
        this._silent = {};
        this._pending = {};
        this._hasData = true;
        this._previousAttributes = _.clone(this.attributes);
        this.initialize.apply(this, arguments);
      };

      /**
       * @lends AV.Object.prototype
       * @property {String} id The objectId of the AV Object.
       */

      /**
       * Saves the given list of AV.Object.
       * If any error is encountered, stops and calls the error handler.
       *
       * <pre>
       *   AV.Object.saveAll([object1, object2, ...]).then(function(list) {
       *     // All the objects were saved.
       *   }, function(error) {
       *     // An error occurred while saving one of the objects.
       *   });
       *
       * @param {Array} list A list of <code>AV.Object</code>.
       */
      AV.Object.saveAll = function(list, options) {
        return AV.Object._deepSaveAsync(list, null, options);
      };

      /**
       * Fetch the given list of AV.Object.
       *
       * @param {AV.Object[]} objects A list of <code>AV.Object</code>
       * @param {AuthOptions} options
       * @return {Promise.<AV.Object[]>} The given list of <code>AV.Object</code>, updated
       */

      AV.Object.fetchAll = (objects, options) =>
        AV.Promise.resolve().then(() =>
          AVRequest('batch', null, null, 'POST', {
            requests: _.map(objects, object => {
              if (!object.className) throw new Error('object must have className to fetch');
              if (!object.id) throw new Error('object must have id to fetch');
              if (object.dirty()) throw new Error('object is modified but not saved');
              return {
                method: 'GET',
                path: `/1.1/classes/${object.className}/${object.id}`,
              };
            }),
          }, options)
        ).then(function(response) {
          _.forEach(objects, function(object, i) {
            if (response[i].success) {
              object._finishFetch(
                object.parse(response[i].success));
            } else {
              const error = new Error(response[i].error.error);
              error.code = response[i].error.code;
              throw error;
            }
          });
          return objects;
        });

      // Attach all inheritable methods to the AV.Object prototype.
      _.extend(AV.Object.prototype, AV.Events,
               /** @lends AV.Object.prototype */ {
        _fetchWhenSave: false,

        /**
         * Initialize is an empty function by default. Override it with your own
         * initialization logic.
         */
        initialize: function(){},

       /**
         * Set whether to enable fetchWhenSave option when updating object.
         * When set true, SDK would fetch the latest object after saving.
         * Default is false.
         *
         * @deprecated use AV.Object#save with options.fetchWhenSave instead
         * @param {boolean} enable  true to enable fetchWhenSave option.
         */
        fetchWhenSave: function(enable){
          console.warn('AV.Object#fetchWhenSave is deprecated, use AV.Object#save with options.fetchWhenSave instead.');
          if (!_.isBoolean(enable)) {
            throw new Error('Expect boolean value for fetchWhenSave');
          }
          this._fetchWhenSave = enable;
        },

       /**
        * Returns the object's objectId.
        * @return {String} the objectId.
        */
        getObjectId: function() {
          return this.id;
        },

       /**
        * Returns the object's createdAt attribute.
        * @return {Date}
        */
        getCreatedAt: function() {
          return this.createdAt || this.get('createdAt');
        },

       /**
        * Returns the object's updatedAt attribute.
        * @return {Date}
        */
        getUpdatedAt: function() {
          return this.updatedAt || this.get('updatedAt');
        },

        /**
         * Returns a JSON version of the object suitable for saving to AV.
         * @return {Object}
         */
        toJSON: function() {
          var json = this._toFullJSON();
          AV._arrayEach(["__type", "className"],
                           function(key) { delete json[key]; });
          return json;
        },

        _toFullJSON: function(seenObjects) {
          var json = _.clone(this.attributes);
          AV._objectEach(json, function(val, key) {
            json[key] = AV._encode(val, seenObjects);
          });
          AV._objectEach(this._operations, function(val, key) {
            json[key] = val;
          });

          if (_.has(this, "id")) {
            json.objectId = this.id;
          }
          _(['createdAt', 'updatedAt']).each((key) => {
            if (_.has(this, key)) {
              const val = this[key];
              json[key] = _.isDate(val) ? val.toJSON() : val;
            }
          });
          json.__type = "Object";
          json.className = this.className;
          return json;
        },

        /**
         * Updates _hashedJSON to reflect the current state of this object.
         * Adds any changed hash values to the set of pending changes.
         * @private
         */
        _refreshCache: function() {
          var self = this;
          if (self._refreshingCache) {
            return;
          }
          self._refreshingCache = true;
          AV._objectEach(this.attributes, function(value, key) {
            if (value instanceof AV.Object) {
              value._refreshCache();
            } else if (_.isObject(value)) {
              if (self._resetCacheForKey(key)) {
                self.set(key, new AV.Op.Set(value), { silent: true });
              }
            }
          });
          delete self._refreshingCache;
        },

        /**
         * Returns true if this object has been modified since its last
         * save/refresh.  If an attribute is specified, it returns true only if that
         * particular attribute has been modified since the last save/refresh.
         * @param {String} attr An attribute name (optional).
         * @return {Boolean}
         */
        dirty: function(attr) {
          this._refreshCache();

          var currentChanges = _.last(this._opSetQueue);

          if (attr) {
            return (currentChanges[attr] ? true : false);
          }
          if (!this.id) {
            return true;
          }
          if (_.keys(currentChanges).length > 0) {
            return true;
          }
          return false;
        },

        /**
         * Gets a Pointer referencing this Object.
         * @private
         */
        _toPointer: function() {
          // if (!this.id) {
          //   throw new Error("Can't serialize an unsaved AV.Object");
          // }
          return { __type: "Pointer",
                   className: this.className,
                   objectId: this.id };
        },

        /**
         * Gets the value of an attribute.
         * @param {String} attr The string name of an attribute.
         */
        get: function(attr) {
          switch (attr) {
            case 'objectId':
              return this.id;
            case 'createdAt':
            case 'updatedAt':
              return this[attr];
            default:
              return this.attributes[attr];
          }
        },

        /**
         * Gets a relation on the given class for the attribute.
         * @param {String} attr The attribute to get the relation for.
         * @return {AV.Relation}
         */
        relation: function(attr) {
          var value = this.get(attr);
          if (value) {
            if (!(value instanceof AV.Relation)) {
              throw new Error("Called relation() on non-relation field " + attr);
            }
            value._ensureParentAndKey(this, attr);
            return value;
          } else {
            return new AV.Relation(this, attr);
          }
        },

        /**
         * Gets the HTML-escaped value of an attribute.
         */
        escape: function(attr) {
          var html = this._escapedAttributes[attr];
          if (html) {
            return html;
          }
          var val = this.attributes[attr];
          var escaped;
          if (utils.isNullOrUndefined(val)) {
            escaped = '';
          } else {
            escaped = _.escape(val.toString());
          }
          this._escapedAttributes[attr] = escaped;
          return escaped;
        },

        /**
         * Returns <code>true</code> if the attribute contains a value that is not
         * null or undefined.
         * @param {String} attr The string name of the attribute.
         * @return {Boolean}
         */
        has: function(attr) {
          return !utils.isNullOrUndefined(this.attributes[attr]);
        },

        /**
         * Pulls "special" fields like objectId, createdAt, etc. out of attrs
         * and puts them on "this" directly.  Removes them from attrs.
         * @param attrs - A dictionary with the data for this AV.Object.
         * @private
         */
        _mergeMagicFields: function(attrs) {
          // Check for changes of magic fields.
          var model = this;
          var specialFields = ["objectId", "createdAt", "updatedAt"];
          AV._arrayEach(specialFields, function(attr) {
            if (attrs[attr]) {
              if (attr === "objectId") {
                model.id = attrs[attr];
              } else if ((attr === "createdAt" || attr === "updatedAt") &&
                         !_.isDate(attrs[attr])) {
                model[attr] = AV._parseDate(attrs[attr]);
              } else {
                model[attr] = attrs[attr];
              }
              delete attrs[attr];
            }
          });
          return attrs;
        },

        /**
         * Returns the json to be sent to the server.
         * @private
         */
        _startSave: function() {
          this._opSetQueue.push({});
        },

        /**
         * Called when a save fails because of an error. Any changes that were part
         * of the save need to be merged with changes made after the save. This
         * might throw an exception is you do conflicting operations. For example,
         * if you do:
         *   object.set("foo", "bar");
         *   object.set("invalid field name", "baz");
         *   object.save();
         *   object.increment("foo");
         * then this will throw when the save fails and the client tries to merge
         * "bar" with the +1.
         * @private
         */
        _cancelSave: function() {
          var self = this;
          var failedChanges = _.first(this._opSetQueue);
          this._opSetQueue = _.rest(this._opSetQueue);
          var nextChanges = _.first(this._opSetQueue);
          AV._objectEach(failedChanges, function(op, key) {
            var op1 = failedChanges[key];
            var op2 = nextChanges[key];
            if (op1 && op2) {
              nextChanges[key] = op2._mergeWithPrevious(op1);
            } else if (op1) {
              nextChanges[key] = op1;
            }
          });
          this._saving = this._saving - 1;
        },

        /**
         * Called when a save completes successfully. This merges the changes that
         * were saved into the known server data, and overrides it with any data
         * sent directly from the server.
         * @private
         */
        _finishSave: function(serverData) {
          // Grab a copy of any object referenced by this object. These instances
          // may have already been fetched, and we don't want to lose their data.
          // Note that doing it like this means we will unify separate copies of the
          // same object, but that's a risk we have to take.
          var fetchedObjects = {};
          AV._traverse(this.attributes, function(object) {
            if (object instanceof AV.Object && object.id && object._hasData) {
              fetchedObjects[object.id] = object;
            }
          });

          var savedChanges = _.first(this._opSetQueue);
          this._opSetQueue = _.rest(this._opSetQueue);
          this._applyOpSet(savedChanges, this._serverData);
          this._mergeMagicFields(serverData);
          var self = this;
          AV._objectEach(serverData, function(value, key) {
            self._serverData[key] = AV._decode(value, key);

            // Look for any objects that might have become unfetched and fix them
            // by replacing their values with the previously observed values.
            var fetched = AV._traverse(self._serverData[key], function(object) {
              if (object instanceof AV.Object && fetchedObjects[object.id]) {
                return fetchedObjects[object.id];
              }
            });
            if (fetched) {
              self._serverData[key] = fetched;
            }
          });
          this._rebuildAllEstimatedData();
          this._saving = this._saving - 1;
        },

        /**
         * Called when a fetch or login is complete to set the known server data to
         * the given object.
         * @private
         */
        _finishFetch: function(serverData, hasData) {
          // Clear out any changes the user might have made previously.
          this._opSetQueue = [{}];

          // Bring in all the new server data.
          this._mergeMagicFields(serverData);
          var self = this;
          AV._objectEach(serverData, function(value, key) {
            self._serverData[key] = AV._decode(value, key);
          });

          // Refresh the attributes.
          this._rebuildAllEstimatedData();

          // Clear out the cache of mutable containers.
          this._refreshCache();
          this._opSetQueue = [{}];

          this._hasData = hasData;
        },

        /**
         * Applies the set of AV.Op in opSet to the object target.
         * @private
         */
        _applyOpSet: function(opSet, target) {
          var self = this;
          AV._objectEach(opSet, function(change, key) {
            target[key] = change._estimate(target[key], self, key);
            if (target[key] === AV.Op._UNSET) {
              delete target[key];
            }
          });
        },

        /**
         * Replaces the cached value for key with the current value.
         * Returns true if the new value is different than the old value.
         * @private
         */
        _resetCacheForKey: function(key) {
          var value = this.attributes[key];
          if (_.isObject(value) &&
              !(value instanceof AV.Object) &&
              !(value instanceof AV.File)) {

            value = value.toJSON ? value.toJSON() : value;
            var json = JSON.stringify(value);
            if (this._hashedJSON[key] !== json) {
              var wasSet = !! this._hashedJSON[key];
              this._hashedJSON[key] = json;
              return wasSet;
            }
          }
          return false;
        },

        /**
         * Populates attributes[key] by starting with the last known data from the
         * server, and applying all of the local changes that have been made to that
         * key since then.
         * @private
         */
        _rebuildEstimatedDataForKey: function(key) {
          var self = this;
          delete this.attributes[key];
          if (this._serverData[key]) {
            this.attributes[key] = this._serverData[key];
          }
          AV._arrayEach(this._opSetQueue, function(opSet) {
            var op = opSet[key];
            if (op) {
              self.attributes[key] = op._estimate(self.attributes[key], self, key);
              if (self.attributes[key] === AV.Op._UNSET) {
                delete self.attributes[key];
              } else {
                self._resetCacheForKey(key);
              }
            }
          });
        },

        /**
         * Populates attributes by starting with the last known data from the
         * server, and applying all of the local changes that have been made since
         * then.
         * @private
         */
        _rebuildAllEstimatedData: function() {
          var self = this;

          var previousAttributes = _.clone(this.attributes);

          this.attributes = _.clone(this._serverData);
          AV._arrayEach(this._opSetQueue, function(opSet) {
            self._applyOpSet(opSet, self.attributes);
            AV._objectEach(opSet, function(op, key) {
              self._resetCacheForKey(key);
            });
          });

          // Trigger change events for anything that changed because of the fetch.
          AV._objectEach(previousAttributes, function(oldValue, key) {
            if (self.attributes[key] !== oldValue) {
              self.trigger('change:' + key, self, self.attributes[key], {});
            }
          });
          AV._objectEach(this.attributes, function(newValue, key) {
            if (!_.has(previousAttributes, key)) {
              self.trigger('change:' + key, self, newValue, {});
            }
          });
        },

        /**
         * Sets a hash of model attributes on the object, firing
         * <code>"change"</code> unless you choose to silence it.
         *
         * <p>You can call it with an object containing keys and values, or with one
         * key and value.  For example:<pre>
         *   gameTurn.set({
         *     player: player1,
         *     diceRoll: 2
         *   }, {
         *     error: function(gameTurnAgain, error) {
         *       // The set failed validation.
         *     }
         *   });
         *
         *   game.set("currentPlayer", player2, {
         *     error: function(gameTurnAgain, error) {
         *       // The set failed validation.
         *     }
         *   });
         *
         *   game.set("finished", true);</pre></p>
         *
         * @param {String} key The key to set.
         * @param {Any} value The value to give it.
         * @param {Object} [options]
         * @param {Boolean} [options.silent]
         * @return {AV.Object} self if succeeded, throws if the value is not valid.
         * @see AV.Object#validate
         */
        set: function(key, value, options) {
          var attrs;
          if (_.isObject(key) || utils.isNullOrUndefined(key)) {
            attrs = _.mapObject(key, function(v, k) {
              checkReservedKey(k);
              return AV._decode(v, k);
            });
            options = value;
          } else {
            attrs = {};
            checkReservedKey(key);
            attrs[key] = AV._decode(value, key);
          }

          // Extract attributes and options.
          options = options || {};
          if (!attrs) {
            return this;
          }
          if (attrs instanceof AV.Object) {
            attrs = attrs.attributes;
          }

          // If the unset option is used, every attribute should be a Unset.
          if (options.unset) {
            AV._objectEach(attrs, function(unused_value, key) {
              attrs[key] = new AV.Op.Unset();
            });
          }

          // Apply all the attributes to get the estimated values.
          var dataToValidate = _.clone(attrs);
          var self = this;
          AV._objectEach(dataToValidate, function(value, key) {
            if (value instanceof AV.Op) {
              dataToValidate[key] = value._estimate(self.attributes[key],
                                                    self, key);
              if (dataToValidate[key] === AV.Op._UNSET) {
                delete dataToValidate[key];
              }
            }
          });

          // Run validation.
          this._validate(attrs, options);

          options.changes = {};
          var escaped = this._escapedAttributes;
          var prev = this._previousAttributes || {};

          // Update attributes.
          AV._arrayEach(_.keys(attrs), function(attr) {
            var val = attrs[attr];

            // If this is a relation object we need to set the parent correctly,
            // since the location where it was parsed does not have access to
            // this object.
            if (val instanceof AV.Relation) {
              val.parent = self;
            }

            if (!(val instanceof AV.Op)) {
              val = new AV.Op.Set(val);
            }

            // See if this change will actually have any effect.
            var isRealChange = true;
            if (val instanceof AV.Op.Set &&
                _.isEqual(self.attributes[attr], val.value)) {
              isRealChange = false;
            }

            if (isRealChange) {
              delete escaped[attr];
              if (options.silent) {
                self._silent[attr] = true;
              } else {
                options.changes[attr] = true;
              }
            }

            var currentChanges = _.last(self._opSetQueue);
            currentChanges[attr] = val._mergeWithPrevious(currentChanges[attr]);
            self._rebuildEstimatedDataForKey(attr);

            if (isRealChange) {
              self.changed[attr] = self.attributes[attr];
              if (!options.silent) {
                self._pending[attr] = true;
              }
            } else {
              delete self.changed[attr];
              delete self._pending[attr];
            }
          });

          if (!options.silent) {
            this.change(options);
          }
          return this;
        },

        /**
         * Remove an attribute from the model, firing <code>"change"</code> unless
         * you choose to silence it. This is a noop if the attribute doesn't
         * exist.
         */
        unset: function(attr, options) {
          options = options || {};
          options.unset = true;
          return this.set(attr, null, options);
        },

        /**
         * Atomically increments the value of the given attribute the next time the
         * object is saved. If no amount is specified, 1 is used by default.
         *
         * @param attr {String} The key.
         * @param amount {Number} The amount to increment by.
         */
        increment: function(attr, amount) {
          if (_.isUndefined(amount) || _.isNull(amount)) {
            amount = 1;
          }
          return this.set(attr, new AV.Op.Increment(amount));
        },

        /**
         * Atomically add an object to the end of the array associated with a given
         * key.
         * @param attr {String} The key.
         * @param item {} The item to add.
         */
        add: function(attr, item) {
          return this.set(attr, new AV.Op.Add(utils.ensureArray(item)));
        },

        /**
         * Atomically add an object to the array associated with a given key, only
         * if it is not already present in the array. The position of the insert is
         * not guaranteed.
         *
         * @param attr {String} The key.
         * @param item {} The object to add.
         */
        addUnique: function(attr, item) {
          return this.set(attr, new AV.Op.AddUnique(utils.ensureArray(item)));
        },

        /**
         * Atomically remove all instances of an object from the array associated
         * with a given key.
         *
         * @param attr {String} The key.
         * @param item {} The object to remove.
         */
        remove: function(attr, item) {
          return this.set(attr, new AV.Op.Remove(utils.ensureArray(item)));
        },

        /**
         * Returns an instance of a subclass of AV.Op describing what kind of
         * modification has been performed on this field since the last time it was
         * saved. For example, after calling object.increment("x"), calling
         * object.op("x") would return an instance of AV.Op.Increment.
         *
         * @param attr {String} The key.
         * @returns {AV.Op} The operation, or undefined if none.
         */
        op: function(attr) {
          return _.last(this._opSetQueue)[attr];
        },

        /**
         * Clear all attributes on the model, firing <code>"change"</code> unless
         * you choose to silence it.
         */
        clear: function(options) {
          options = options || {};
          options.unset = true;
          var keysToClear = _.extend(this.attributes, this._operations);
          return this.set(keysToClear, options);
        },

        /**
         * Returns a JSON-encoded set of operations to be sent with the next save
         * request.
         * @private
         */
        _getSaveJSON: function() {
          var json = _.clone(_.first(this._opSetQueue));
          AV._objectEach(json, function(op, key) {
            json[key] = op.toJSON();
          });
          return json;
        },

        /**
         * Returns true if this object can be serialized for saving.
         * @private
         */
        _canBeSerialized: function() {
          return AV.Object._canBeSerializedAsValue(this.attributes);
        },

        /**
         * Fetch the model from the server. If the server's representation of the
         * model differs from its current attributes, they will be overriden,
         * triggering a <code>"change"</code> event.
         * @param {Object} fetchOptions Optional options to set 'keys',
         *      'include' and 'includeACL' option.
         * @param {AuthOptions} options
         * @return {Promise} A promise that is fulfilled when the fetch
         *     completes.
         */
        fetch: function(fetchOptions, options) {

          var self = this;
          var request = AVRequest('classes', this.className, this.id, 'GET',
                                    utils.transformFetchOptions(fetchOptions), options);
          return request.then(function(response) {
            self._finishFetch(self.parse(response), true);
            return self;
          });
        },

        /**
         * Set a hash of model attributes, and save the model to the server.
         * updatedAt will be updated when the request returns.
         * You can either call it as:<pre>
         *   object.save();</pre>
         * or<pre>
         *   object.save(null, options);</pre>
         * or<pre>
         *   object.save(attrs, options);</pre>
         * or<pre>
         *   object.save(key, value, options);</pre>
         *
         * For example, <pre>
         *   gameTurn.save({
         *     player: "Jake Cutter",
         *     diceRoll: 2
         *   }).then(function(gameTurnAgain) {
         *     // The save was successful.
         *   }, function(error) {
         *     // The save failed.  Error is an instance of AVError.
         *   });</pre>
         * @param {AuthOptions} options AuthOptions plus:
         * @param {Boolean} options.fetchWhenSave fetch and update object after save succeeded
         * @param {AV.Query} options.query Save object only when it matches the query
         * @return {AV.Promise} A promise that is fulfilled when the save
         *     completes.
         * @see AVError
         */
        save: function(arg1, arg2, arg3) {
          var i, attrs, current, options, saved;
          if (_.isObject(arg1) || utils.isNullOrUndefined(arg1)) {
            attrs = arg1;
            options = arg2;
          } else {
            attrs = {};
            attrs[arg1] = arg2;
            options = arg3;
          }

          options = _.clone(options) || {};
          if (options.wait) {
            current = _.clone(this.attributes);
          }

          var setOptions = _.clone(options) || {};
          if (setOptions.wait) {
            setOptions.silent = true;
          }
          if (attrs) {
            this.set(attrs, setOptions);
          }

          var model = this;

          // If there is any unsaved child, save it first.
          model._refreshCache();

          var unsavedChildren = [];
          var unsavedFiles = [];
          AV.Object._findUnsavedChildren(model.attributes,
                                            unsavedChildren,
                                            unsavedFiles);
          if (unsavedChildren.length + unsavedFiles.length > 0) {
            return AV.Object._deepSaveAsync(this.attributes, model, options).then(function() {
              return model.save(null, options);
            });
          }

          this._startSave();
          this._saving = (this._saving || 0) + 1;

          this._allPreviousSaves = this._allPreviousSaves || AV.Promise.resolve();
          this._allPreviousSaves = this._allPreviousSaves.catch(e => {}).then(function() {
            var method = model.id ? 'PUT' : 'POST';

            var json = model._getSaveJSON();

            if(model._fetchWhenSave){
              //Sepcial-case fetchWhenSave when updating object.
              json._fetchWhenSave = true;
            }

            if (options.fetchWhenSave) {
              json._fetchWhenSave = true;
            }
            if (options.query) {
              var queryJSON;
              if (typeof options.query.toJSON === 'function') {
                queryJSON = options.query.toJSON();
                if (queryJSON) {
                  json._where = queryJSON.where;
                }
              }
              if (!json._where) {
                var error = new Error('options.query is not an AV.Query');
                throw error;
              }
            }

            _.extend(json, model._flags);

            var route = "classes";
            var className = model.className;
            if (model.className === "_User" && !model.id) {
              // Special-case user sign-up.
              route = "users";
              className = null;
            }
            //hook makeRequest in options.
            var makeRequest = options._makeRequest || AVRequest;
            var request = makeRequest(route, className, model.id, method, json, options);

            request = request.then(function(resp) {
              var serverAttrs = model.parse(resp);
              if (options.wait) {
                serverAttrs = _.extend(attrs || {}, serverAttrs);
              }
              model._finishSave(serverAttrs);
              if (options.wait) {
                model.set(current, setOptions);
              }
              return model;

            }, function(error) {
              model._cancelSave();
              throw error;
            });

            return request;
          });
          return this._allPreviousSaves;
        },

        /**
         * Destroy this model on the server if it was already persisted.
         * Optimistically removes the model from its collection, if it has one.
         * @param {AuthOptions} options AuthOptions plus:
         * @param {Boolean} [options.wait] wait for the server to respond
         * before removal.
         *
         * @return {Promise} A promise that is fulfilled when the destroy
         *     completes.
         */
        destroy: function(options) {
          options = options || {};
          var model = this;

          var triggerDestroy = function() {
            model.trigger('destroy', model, model.collection, options);
          };

          if (!this.id) {
            return triggerDestroy();
          }

          if (!options.wait) {
            triggerDestroy();
          }

          var request =
              AVRequest('classes', this.className, this.id, 'DELETE', this._flags, options);
          return request.then(function() {
            if (options.wait) {
              triggerDestroy();
            }
            return model;
          });
        },

        /**
         * Converts a response into the hash of attributes to be set on the model.
         * @ignore
         */
        parse: function(resp) {
          var output = _.clone(resp);
          _(["createdAt", "updatedAt"]).each(function(key) {
            if (output[key]) {
              output[key] = AV._parseDate(output[key]);
            }
          });
          if (!output.updatedAt) {
            output.updatedAt = output.createdAt;
          }
          return output;
        },

        /**
         * Creates a new model with identical attributes to this one.
         * @return {AV.Object}
         */
        clone: function() {
          return new this.constructor(this.attributes);
        },

        /**
         * Returns true if this object has never been saved to AV.
         * @return {Boolean}
         */
        isNew: function() {
          return !this.id;
        },

        /**
         * Call this method to manually fire a `"change"` event for this model and
         * a `"change:attribute"` event for each changed attribute.
         * Calling this will cause all objects observing the model to update.
         */
        change: function(options) {
          options = options || {};
          var changing = this._changing;
          this._changing = true;

          // Silent changes become pending changes.
          var self = this;
          AV._objectEach(this._silent, function(attr) {
            self._pending[attr] = true;
          });

          // Silent changes are triggered.
          var changes = _.extend({}, options.changes, this._silent);
          this._silent = {};
          AV._objectEach(changes, function(unused_value, attr) {
            self.trigger('change:' + attr, self, self.get(attr), options);
          });
          if (changing) {
            return this;
          }

          // This is to get around lint not letting us make a function in a loop.
          var deleteChanged = function(value, attr) {
            if (!self._pending[attr] && !self._silent[attr]) {
              delete self.changed[attr];
            }
          };

          // Continue firing `"change"` events while there are pending changes.
          while (!_.isEmpty(this._pending)) {
            this._pending = {};
            this.trigger('change', this, options);
            // Pending and silent changes still remain.
            AV._objectEach(this.changed, deleteChanged);
            self._previousAttributes = _.clone(this.attributes);
          }

          this._changing = false;
          return this;
        },

        /**
         * Determine if the model has changed since the last <code>"change"</code>
         * event.  If you specify an attribute name, determine if that attribute
         * has changed.
         * @param {String} attr Optional attribute name
         * @return {Boolean}
         */
        hasChanged: function(attr) {
          if (!arguments.length) {
            return !_.isEmpty(this.changed);
          }
          return this.changed && _.has(this.changed, attr);
        },

        /**
         * Returns an object containing all the attributes that have changed, or
         * false if there are no changed attributes. Useful for determining what
         * parts of a view need to be updated and/or what attributes need to be
         * persisted to the server. Unset attributes will be set to undefined.
         * You can also pass an attributes object to diff against the model,
         * determining if there *would be* a change.
         */
        changedAttributes: function(diff) {
          if (!diff) {
            return this.hasChanged() ? _.clone(this.changed) : false;
          }
          var changed = {};
          var old = this._previousAttributes;
          AV._objectEach(diff, function(diffVal, attr) {
            if (!_.isEqual(old[attr], diffVal)) {
              changed[attr] = diffVal;
            }
          });
          return changed;
        },

        /**
         * Gets the previous value of an attribute, recorded at the time the last
         * <code>"change"</code> event was fired.
         * @param {String} attr Name of the attribute to get.
         */
        previous: function(attr) {
          if (!arguments.length || !this._previousAttributes) {
            return null;
          }
          return this._previousAttributes[attr];
        },

        /**
         * Gets all of the attributes of the model at the time of the previous
         * <code>"change"</code> event.
         * @return {Object}
         */
        previousAttributes: function() {
          return _.clone(this._previousAttributes);
        },

        /**
         * Checks if the model is currently in a valid state. It's only possible to
         * get into an *invalid* state if you're using silent changes.
         * @return {Boolean}
         */
        isValid: function() {
          try {
            this.validate(this.attributes);
          } catch (error) {
            return false;
          }
          return true;
        },

        /**
         * You should not call this function directly unless you subclass
         * <code>AV.Object</code>, in which case you can override this method
         * to provide additional validation on <code>set</code> and
         * <code>save</code>.  Your implementation should throw an Error if
         * the attrs is invalid
         *
         * @param {Object} attrs The current data to validate.
         * @see AV.Object#set
         */
        validate: function(attrs) {
          if (_.has(attrs, "ACL") && !(attrs.ACL instanceof AV.ACL)) {
            throw new AVError(AVError.OTHER_CAUSE,
                                   "ACL must be a AV.ACL.");
          }
        },

        /**
         * Run validation against a set of incoming attributes, returning `true`
         * if all is well. If a specific `error` callback has been passed,
         * call that instead of firing the general `"error"` event.
         * @private
         */
        _validate: function(attrs, options) {
          if (options.silent || !this.validate) {
            return;
          }
          attrs = _.extend({}, this.attributes, attrs);
          this.validate(attrs);
        },

        /**
         * Returns the ACL for this object.
         * @returns {AV.ACL} An instance of AV.ACL.
         * @see AV.Object#get
         */
        getACL: function() {
          return this.get("ACL");
        },

        /**
         * Sets the ACL to be used for this object.
         * @param {AV.ACL} acl An instance of AV.ACL.
         * @param {Object} options Optional Backbone-like options object to be
         *     passed in to set.
         * @return {Boolean} Whether the set passed validation.
         * @see AV.Object#set
         */
        setACL: function(acl, options) {
          return this.set("ACL", acl, options);
        },

        disableBeforeHook: function() {
          this.ignoreHook('beforeSave');
          this.ignoreHook('beforeUpdate');
          this.ignoreHook('beforeDelete');
        },

        disableAfterHook: function() {
          this.ignoreHook('afterSave');
          this.ignoreHook('afterUpdate');
          this.ignoreHook('afterDelete');
        },

        ignoreHook: function(hookName) {
          if (!_.contains(['beforeSave', 'afterSave', 'beforeUpdate', 'afterUpdate', 'beforeDelete', 'afterDelete'], hookName)) {
            console.trace('Unsupported hookName: ' + hookName);
          }

          if (!AV.hookKey) {
            console.trace('ignoreHook required hookKey');
          }

          if (!this._flags.__ignore_hooks) {
            this._flags.__ignore_hooks = [];
          }

          this._flags.__ignore_hooks.push(hookName);
        }
      });

       /**
        * Creates an instance of a subclass of AV.Object for the give classname
        * and id.
        * @param  {String} className The name of the AV class backing this model.
        * @param {String} id The object id of this model.
        * @return {AV.Object} A new subclass instance of AV.Object.
        */
       AV.Object.createWithoutData = function(className, id, hasData){
         var result = AV.Object._create(className, undefined, undefined, /* noDefaultACL*/ true);
         result.id = id;
         result._hasData = hasData;
         return result;
       };
       /**
        * Delete objects in batch.
        * @param {AV.Object[]} objects The <code>AV.Object</code> array to be deleted.
        * @param {AuthOptions} options
        * @return {Promise} A promise that is fulfilled when the save
        *     completes.
        */
       AV.Object.destroyAll = function(objects, options = {}){
          if (!objects || objects.length === 0){
    		    return AV.Promise.resolve();
          }
          const objectsByClassNameAndFlags = _.groupBy(objects, object => JSON.stringify({
            className: object.className,
            flags: object._flags
          }));
          const body = {
            requests: _.map(objectsByClassNameAndFlags, objects => {
              const ids = _.map(objects, 'id').join(',');
              return {
                method: 'DELETE',
                path: `/1.1/classes/${objects[0].className}/${ids}`,
                body: objects[0]._flags
              }
            })
          };
          return AVRequest('batch', null, null, 'POST', body, options);
       };

      /**
       * Returns the appropriate subclass for making new instances of the given
       * className string.
       * @private
       */
      AV.Object._getSubclass = function(className) {
        if (!_.isString(className)) {
          throw new Error('AV.Object._getSubclass requires a string argument.');
        }
        var ObjectClass = AV.Object._classMap[className];
        if (!ObjectClass) {
          ObjectClass = AV.Object.extend(className);
          AV.Object._classMap[className] = ObjectClass;
        }
        return ObjectClass;
      };

      /**
       * Creates an instance of a subclass of AV.Object for the given classname.
       * @private
       */
      AV.Object._create = function(className, attributes, options, noDefaultACL) {
        var ObjectClass = AV.Object._getSubclass(className);
        return new ObjectClass(attributes, options, noDefaultACL);
      };

      // Set up a map of className to class so that we can create new instances of
      // AV Objects from JSON automatically.
      AV.Object._classMap = {};

      AV.Object._extend = AV._extend;

      /**
       * Creates a new model with defined attributes,
       * It's the same with
       * <pre>
       *   new AV.Object(attributes, options);
       *  </pre>
       * @param {Object} attributes The initial set of data to store in the object.
       * @param {Object} options A set of Backbone-like options for creating the
       *     object.  The only option currently supported is "collection".
       * @return {AV.Object}
       * @since v0.4.4
       * @see AV.Object
       * @see AV.Object.extend
       */
      AV.Object['new'] = function(attributes, options){
        return new AV.Object(attributes, options);
      };

      /**
       * Creates a new subclass of AV.Object for the given AV class name.
       *
       * <p>Every extension of a AV class will inherit from the most recent
       * previous extension of that class. When a AV.Object is automatically
       * created by parsing JSON, it will use the most recent extension of that
       * class.</p>
       *
       * <p>You should call either:<pre>
       *     var MyClass = AV.Object.extend("MyClass", {
       *         <i>Instance properties</i>
       *     }, {
       *         <i>Class properties</i>
       *     });</pre>
       * or, for Backbone compatibility:<pre>
       *     var MyClass = AV.Object.extend({
       *         className: "MyClass",
       *         <i>Other instance properties</i>
       *     }, {
       *         <i>Class properties</i>
       *     });</pre></p>
       *
       * @param {String} className The name of the AV class backing this model.
       * @param {Object} protoProps Instance properties to add to instances of the
       *     class returned from this method.
       * @param {Object} classProps Class properties to add the class returned from
       *     this method.
       * @return {Class} A new subclass of AV.Object.
       */
      AV.Object.extend = function(className, protoProps, classProps) {
        // Handle the case with only two args.
        if (!_.isString(className)) {
          if (className && _.has(className, "className")) {
            return AV.Object.extend(className.className, className, protoProps);
          } else {
            throw new Error(
                "AV.Object.extend's first argument should be the className.");
          }
        }

        // If someone tries to subclass "User", coerce it to the right type.
        if (className === "User") {
          className = "_User";
        }

        var NewClassObject = null;
        if (_.has(AV.Object._classMap, className)) {
          var OldClassObject = AV.Object._classMap[className];
          // This new subclass has been told to extend both from "this" and from
          // OldClassObject. This is multiple inheritance, which isn't supported.
          // For now, let's just pick one.
          if (protoProps || classProps) {
            NewClassObject = OldClassObject._extend(protoProps, classProps);
          } else {
            return OldClassObject;
          }
        } else {
          protoProps = protoProps || {};
          protoProps._className = className;
          NewClassObject = this._extend(protoProps, classProps);
        }
        // Extending a subclass should reuse the classname automatically.
        NewClassObject.extend = function(arg0) {
          if (_.isString(arg0) || (arg0 && _.has(arg0, "className"))) {
            return AV.Object.extend.apply(NewClassObject, arguments);
          }
          var newArguments = [className].concat(_.toArray(arguments));
          return AV.Object.extend.apply(NewClassObject, newArguments);
        };
        NewClassObject['new'] = function(attributes, options){
          return new NewClassObject(attributes, options);
        };
        AV.Object._classMap[className] = NewClassObject;
        return NewClassObject;
      };

      // ES6 class syntax support
      Object.defineProperty(AV.Object.prototype, 'className', {
        get: function(){
          const className = this._className || this.constructor._LCClassName || this.constructor.name;
          // If someone tries to subclass "User", coerce it to the right type.
          if (className === "User") {
            return "_User";
          }
          return className;
        },
      });

      /**
       * Register a class.
       * If a subclass of <code>AV.Object</code> is defined with your own implement
       * rather then <code>AV.Object.extend</code>, the subclass must be registered.
       * @param {Function} klass A subclass of <code>AV.Object</code>
       * @param {String} [name] Specify the name of the class. Useful when the class might be uglified.
       * @example
       * class Person extend AV.Object {}
       * AV.Object.register(Person);
       */
      AV.Object.register = (klass, name) => {
        if (!(klass.prototype instanceof AV.Object)) {
          throw new Error('registered class is not a subclass of AV.Object');
        }
        const className = name || klass.name;
        if (!className.length) {
          throw new Error('registered class must be named');
        }
        if (name) {
          klass._LCClassName = name;
        }
        AV.Object._classMap[className] = klass;
      };

      AV.Object._findUnsavedChildren = function(object, children, files) {
        AV._traverse(object, function(object) {
          if (object instanceof AV.Object) {
            object._refreshCache();
            if (object.dirty()) {
              children.push(object);
            }
            return;
          }

          if (object instanceof AV.File) {
            if (!object.url() && !object.id) {
              files.push(object);
            }
            return;
          }
        });
      };

      AV.Object._canBeSerializedAsValue = function(object) {
        var canBeSerializedAsValue = true;

        if (object instanceof AV.Object || object instanceof AV.File) {
          canBeSerializedAsValue = !!object.id;

        } else if (_.isArray(object)) {
          AV._arrayEach(object, function(child) {
            if (!AV.Object._canBeSerializedAsValue(child)) {
              canBeSerializedAsValue = false;
            }
          });

        } else if (_.isObject(object)) {
          AV._objectEach(object, function(child) {
            if (!AV.Object._canBeSerializedAsValue(child)) {
              canBeSerializedAsValue = false;
            }
          });
        }

        return canBeSerializedAsValue;
      };

      AV.Object._deepSaveAsync = function(object, model, options) {
        var unsavedChildren = [];
        var unsavedFiles = [];
        AV.Object._findUnsavedChildren(object, unsavedChildren, unsavedFiles);
        if(model) {
          unsavedChildren = _.filter(unsavedChildren, function(object) {
            return object != model;
          });
        }

        var promise = AV.Promise.resolve();
        _.each(unsavedFiles, function(file) {
          promise = promise.then(function() {
            return file.save();
          });
        });

        var objects = _.uniq(unsavedChildren);
        var remaining = _.uniq(objects);

        return promise.then(function() {
          return AV.Promise._continueWhile(function() {
            return remaining.length > 0;
          }, function() {

            // Gather up all the objects that can be saved in this batch.
            var batch = [];
            var newRemaining = [];
            AV._arrayEach(remaining, function(object) {
              // Limit batches to 20 objects.
              if (batch.length > 20) {
                newRemaining.push(object);
                return;
              }

              if (object._canBeSerialized()) {
                batch.push(object);
              } else {
                newRemaining.push(object);
              }
            });
            remaining = newRemaining;

            // If we can't save any objects, there must be a circular reference.
            if (batch.length === 0) {
              return AV.Promise.reject(
                new AVError(AVError.OTHER_CAUSE,
                                "Tried to save a batch with a cycle."));
            }

            // Reserve a spot in every object's save queue.
            var readyToStart = AV.Promise.resolve(_.map(batch, function(object) {
              return object._allPreviousSaves || AV.Promise.resolve();
            }));

            // Save a single batch, whether previous saves succeeded or failed.
            const bathSavePromise = readyToStart.then(() =>
              AVRequest("batch", null, null, "POST", {
                requests: _.map(batch, function(object) {
                  var json = object._getSaveJSON();
                  _.extend(json, object._flags);
                  var method = "POST";

                  var path = "/1.1/classes/" + object.className;
                  if (object.id) {
                    path = path + "/" + object.id;
                    method = "PUT";
                  }

                  object._startSave();

                  return {
                    method: method,
                    path: path,
                    body: json
                  };
                })

              }, options).then(function(response) {
                var error;
                AV._arrayEach(batch, function(object, i) {
                  if (response[i].success) {
                    object._finishSave(
                      object.parse(response[i].success));
                  } else {
                    error = error || response[i].error;
                    object._cancelSave();
                  }
                });
                if (error) {
                  return AV.Promise.reject(
                    new AVError(error.code, error.error));
                }

              })
            );
            AV._arrayEach(batch, function(object) {
              object._allPreviousSaves = bathSavePromise;
            });
            return bathSavePromise;
          });
        }).then(function() {
          return object;
        });
      };

    };