The source code

    /*!
     * Ext JS Library 3.4.0
     * Copyright(c) 2006-2011 Sencha Inc.
     * licensing@sencha.com
     * http://www.sencha.com/license
     */
    /**
     * @class Ext.data.Record
     * Instances of this class encapsulate both Record definition information, and Record
     * value information for use in {@link Ext.data.Store} objects, or any code which needs
     * to access Records cached in an {@link Ext.data.Store} object.
     * Constructors for this class are generated by passing an Array of field definition objects to {@link #create}.
     * Instances are usually only created by {@link Ext.data.Reader} implementations when processing unformatted data
     * objects.
     * Note that an instance of a Record class may only belong to one {@link Ext.data.Store Store} at a time.
     * In order to copy data from one Store to another, use the {@link #copy} method to create an exact
     * copy of the Record, and insert the new instance into the other Store.
     * When serializing a Record for submission to the server, be aware that it contains many private
     * properties, and also a reference to its owning Store which in turn holds references to its Records.
     * This means that a whole Record may not be encoded using {@link Ext.util.JSON.encode}. Instead, use the
     * {@link #data} and {@link #id} properties.
     * Record objects generated by this constructor inherit all the methods of Ext.data.Record listed below.
     * @constructor
     * This constructor should not be used to create Record objects. Instead, use {@link #create} to
     * generate a subclass of Ext.data.Record configured with information about its constituent fields.
     * The generated constructor has the same signature as this constructor.
     * @param {Object} data (Optional) An object, the properties of which provide values for the new Record's
     * fields. If not specified the {@link Ext.data.Field#defaultValue defaultValue}
     * for each field will be assigned.
     * @param {Object} id (Optional) The id of the Record. The id is used by the
     * {@link Ext.data.Store} object which owns the Record to index its collection
     * of Records (therefore this id should be unique within each store). If an
     * id is not specified a {@link #phantom}
     * Record will be created with an {@link #Record.id automatically generated id}.
     */
    Ext.data.Record = function(data, id){
        // if no id, call the auto id method
        this.id = (id || id === 0) ? id : Ext.data.Record.id(this);
        this.data = data || {};
    };

    /**
     * Generate a constructor for a specific Record layout.
     * @param {Array} o An Array of {@link Ext.data.Field Field} definition objects.
     * The constructor generated by this method may be used to create new Record instances. The data
     * object must contain properties named after the {@link Ext.data.Field field}
     * {@link Ext.data.Field#name}s.  Example usage:
    // create a Record constructor from a description of the fields
    var TopicRecord = Ext.data.Record.create([ // creates a subclass of Ext.data.Record
        {{@link Ext.data.Field#name name}: 'title', {@link Ext.data.Field#mapping mapping}: 'topic_title'},
        {name: 'author', mapping: 'username', allowBlank: false},
        {name: 'totalPosts', mapping: 'topic_replies', type: 'int'},
        {name: 'lastPost', mapping: 'post_time', type: 'date'},
        {name: 'lastPoster', mapping: 'user2'},
        {name: 'excerpt', mapping: 'post_text', allowBlank: false},
        // In the simplest case, if no properties other than name are required,
        // a field definition may consist of just a String for the field name.
        'signature'
    ]);

    // create Record instance
    var myNewRecord = new TopicRecord(
        {
            title: 'Do my job please',
            author: 'noobie',
            totalPosts: 1,
            lastPost: new Date(),
            lastPoster: 'Animal',
            excerpt: 'No way dude!',
            signature: ''
        },
        id // optionally specify the id of the record otherwise {@link #Record.id one is auto-assigned}
    );
    myStore.{@link Ext.data.Store#add add}(myNewRecord);

     * @method create
     * @return {Function} A constructor which is used to create new Records according
     * to the definition. The constructor has the same signature as {@link #Record}.
     * @static
     */
    Ext.data.Record.create = function(o){
        var f = Ext.extend(Ext.data.Record, {});
        var p = f.prototype;
        p.fields = new Ext.util.MixedCollection(false, function(field){
            return field.name;
        });
        for(var i = 0, len = o.length; i < len; i++){
            p.fields.add(new Ext.data.Field(o[i]));
        }
        f.getField = function(name){
            return p.fields.get(name);
        };
        return f;
    };

    Ext.data.Record.PREFIX = 'ext-record';
    Ext.data.Record.AUTO_ID = 1;
    Ext.data.Record.EDIT = 'edit';
    Ext.data.Record.REJECT = 'reject';
    Ext.data.Record.COMMIT = 'commit';

    /**
     * Generates a sequential id. This method is typically called when a record is {@link #create}d
     * and {@link #Record no id has been specified}. The returned id takes the form:
     * {PREFIX}-{AUTO_ID}.
     * PREFIX : StringExt.data.Record.PREFIX
     * (defaults to 'ext-record')
     * AUTO_ID : StringExt.data.Record.AUTO_ID
     * (defaults to 1 initially)
     *
     * @param {Record} rec The record being created.  The record does not exist, it's a {@link #phantom}.
     * @return {String} auto-generated string id, "ext-record-i++';
     */
    Ext.data.Record.id = function(rec) {
        rec.phantom = true;
        return [Ext.data.Record.PREFIX, '-', Ext.data.Record.AUTO_ID++].join('');
    };

    Ext.data.Record.prototype = {
        /**
         * This property is stored in the Record definition's prototype
         * A MixedCollection containing the defined {@link Ext.data.Field Field}s for this Record.  Read-only.
         * @property fields
         * @type Ext.util.MixedCollection
         */
        /**
         * An object hash representing the data for this Record. Every field name in the Record definition
         * is represented by a property of that name in this object. Note that unless you specified a field
         * with {@link Ext.data.Field#name name} "id" in the Record definition, this will not contain
         * an id property.
         * @property data
         * @type {Object}
         */
        /**
         * The unique ID of the Record {@link #Record as specified at construction time}.
         * @property id
         * @type {Object}
         */
        /**
         * Only present if this Record was created by an {@link Ext.data.XmlReader XmlReader}.
         * The XML element which was the source of the data for this Record.
         * @property node
         * @type {XMLElement}
         */
        /**
         * Only present if this Record was created by an {@link Ext.data.ArrayReader ArrayReader} or a {@link Ext.data.JsonReader JsonReader}.
         * The Array or object which was the source of the data for this Record.
         * @property json
         * @type {Array|Object}
         */
        /**
         * Readonly flag - true if this Record has been modified.
         * @type Boolean
         */
        dirty : false,
        editing : false,
        error : null,
        /**
         * This object contains a key and value storing the original values of all modified
         * fields or is null if no fields have been modified.
         * @property modified
         * @type {Object}
         */
        modified : null,
        /**
         * true when the record does not yet exist in a server-side database (see
         * {@link #markDirty}).  Any record which has a real database pk set as its id property
         * is NOT a phantom -- it's real.
         * @property phantom
         * @type {Boolean}
         */
        phantom : false,

        // private
        join : function(store){
            /**
             * The {@link Ext.data.Store} to which this Record belongs.
             * @property store
             * @type {Ext.data.Store}
             */
            this.store = store;
        },

        /**
         * Set the {@link Ext.data.Field#name named field} to the specified value.  For example:
         *
    // record has a field named 'firstname'
    var Employee = Ext.data.Record.{@link #create}([
        {name: 'firstname'},
        ...
    ]);

    // update the 2nd record in the store:
    var rec = myStore.{@link Ext.data.Store#getAt getAt}(1);

    // set the value (shows dirty flag):
    rec.set('firstname', 'Betty');

    // commit the change (removes dirty flag):
    rec.{@link #commit}();

    // update the record in the store, bypass setting dirty flag,
    // and do not store the change in the {@link Ext.data.Store#getModifiedRecords modified records}
    rec.{@link #data}['firstname'] = 'Wilma'; // updates record, but not the view
    rec.{@link #commit}(); // updates the view
         *
         * Notes:
         * If the store has a writer and autoSave=true, each set()
         * will execute an XHR to the server.
         * Use {@link #beginEdit} to prevent the store's update
         * event firing while using set().
         * Use {@link #endEdit} to have the store's update
         * event fire.
         *
         * @param {String} name The {@link Ext.data.Field#name name of the field} to set.
         * @param {String/Object/Array} value The value to set the field to.
         */
        set : function(name, value){
            var encode = Ext.isPrimitive(value) ? String : Ext.encode;
            if(encode(this.data[name]) == encode(value)) {
                return;
            }
            this.dirty = true;
            if(!this.modified){
                this.modified = {};
            }
            if(this.modified[name] === undefined){
                this.modified[name] = this.data[name];
            }
            this.data[name] = value;
            if(!this.editing){
                this.afterEdit();
            }
        },

        // private
        afterEdit : function(){
            if (this.store != undefined && typeof this.store.afterEdit == "function") {
                this.store.afterEdit(this);
            }
        },

        // private
        afterReject : function(){
            if(this.store){
                this.store.afterReject(this);
            }
        },

        // private
        afterCommit : function(){
            if(this.store){
                this.store.afterCommit(this);
            }
        },

        /**
         * Get the value of the {@link Ext.data.Field#name named field}.
         * @param {String} name The {@link Ext.data.Field#name name of the field} to get the value of.
         * @return {Object} The value of the field.
         */
        get : function(name){
            return this.data[name];
        },

        /**
         * Begin an edit. While in edit mode, no events (e.g.. the update event)
         * are relayed to the containing store.
         * See also: {@link #endEdit} and {@link #cancelEdit}.
         */
        beginEdit : function(){
            this.editing = true;
            this.modified = this.modified || {};
        },

        /**
         * Cancels all changes made in the current edit operation.
         */
        cancelEdit : function(){
            this.editing = false;
            delete this.modified;
        },

        /**
         * End an edit. If any data was modified, the containing store is notified
         * (ie, the store's update event will fire).
         */
        endEdit : function(){
            this.editing = false;
            if(this.dirty){
                this.afterEdit();
            }
        },

        /**
         * Usually called by the {@link Ext.data.Store} which owns the Record.
         * Rejects all changes made to the Record since either creation, or the last commit operation.
         * Modified fields are reverted to their original values.
         * Developers should subscribe to the {@link Ext.data.Store#update} event
         * to have their code notified of reject operations.
         * @param {Boolean} silent (optional) True to skip notification of the owning
         * store of the change (defaults to false)
         */
        reject : function(silent){
            var m = this.modified;
            for(var n in m){
                if(typeof m[n] != "function"){
                    this.data[n] = m[n];
                }
            }
            this.dirty = false;
            delete this.modified;
            this.editing = false;
            if(silent !== true){
                this.afterReject();
            }
        },

        /**
         * Usually called by the {@link Ext.data.Store} which owns the Record.
         * Commits all changes made to the Record since either creation, or the last commit operation.
         * Developers should subscribe to the {@link Ext.data.Store#update} event
         * to have their code notified of commit operations.
         * @param {Boolean} silent (optional) True to skip notification of the owning
         * store of the change (defaults to false)
         */
        commit : function(silent){
            this.dirty = false;
            delete this.modified;
            this.editing = false;
            if(silent !== true){
                this.afterCommit();
            }
        },

        /**
         * Gets a hash of only the fields that have been modified since this Record was created or commited.
         * @return Object
         */
        getChanges : function(){
            var m = this.modified, cs = {};
            for(var n in m){
                if(m.hasOwnProperty(n)){
                    cs[n] = this.data[n];
                }
            }
            return cs;
        },

        // private
        hasError : function(){
            return this.error !== null;
        },

        // private
        clearError : function(){
            this.error = null;
        },

        /**
         * Creates a copy (clone) of this Record.
         * @param {String} id (optional) A new Record id, defaults to the id
         * of the record being copied. See {@link #id}.
         * To generate a phantom record with a new id use:
    var rec = record.copy(); // clone the record
    Ext.data.Record.id(rec); // automatically generate a unique sequential id
         *
         * @return {Record}
         */
        copy : function(newId) {
            return new this.constructor(Ext.apply({}, this.data), newId || this.id);
        },

        /**
         * Returns true if the passed field name has been {@link #modified}
         * since the load or last commit.
         * @param {String} fieldName {@link Ext.data.Field.{@link Ext.data.Field#name}
         * @return {Boolean}
         */
        isModified : function(fieldName){
            return !!(this.modified && this.modified.hasOwnProperty(fieldName));
        },

        /**
         * By default returns false if any {@link Ext.data.Field field} within the
         * record configured with {@link Ext.data.Field#allowBlank} = false returns
         * true from an {@link Ext}.{@link Ext#isEmpty isempty} test.
         * @return {Boolean}
         */
        isValid : function() {
            return this.fields.find(function(f) {
                return (f.allowBlank === false && Ext.isEmpty(this.data[f.name])) ? true : false;
            },this) ? false : true;
        },

        /**
         * Marks this Record as {@link #dirty}.  This method
         * is used interally when adding {@link #phantom} records to a
         * {@link Ext.data.Store#writer writer enabled store}.
         *
    Marking a record {@link #dirty} causes the phantom to
         * be returned by {@link Ext.data.Store#getModifiedRecords} where it will
         * have a create action composed for it during {@link Ext.data.Store#save store save}
         * operations.
         */
        markDirty : function(){
            this.dirty = true;
            if(!this.modified){
                this.modified = {};
            }
            this.fields.each(function(f) {
                this.modified[f.name] = this.data[f.name];
            },this);
        }
    };