The source code

    /**
     * @class Ext.data.DataReader
     * Abstract base class for reading structured data from a data source and converting
     * it into an object containing {@link Ext.data.Record} objects and metadata for use
     * by an {@link Ext.data.Store}.  This class is intended to be extended and should not
     * be created directly. For existing implementations, see {@link Ext.data.ArrayReader},
     * {@link Ext.data.JsonReader} and {@link Ext.data.XmlReader}.
     * @constructor Create a new DataReader
     * @param {Object} meta Metadata configuration options (implementation-specific).
     * @param {Array/Object} recordType
     * Either an Array of {@link Ext.data.Field Field} definition objects (which
     * will be passed to {@link Ext.data.Record#create}, or a {@link Ext.data.Record Record}
     * constructor created using {@link Ext.data.Record#create}.
     */
    Ext.data.DataReader = function(meta, recordType){
        /**
         * This DataReader's configured metadata as passed to the constructor.
         * @type Mixed
         * @property meta
         */
        this.meta = meta;
        /**
         * @cfg {Array/Object} fields
         * Either an Array of {@link Ext.data.Field Field} definition objects (which
         * will be passed to {@link Ext.data.Record#create}, or a {@link Ext.data.Record Record}
         * constructor created from {@link Ext.data.Record#create}.
         */
        this.recordType = Ext.isArray(recordType) ?
            Ext.data.Record.create(recordType) : recordType;

        // make sure extraction functions are defined.
        this.buildExtractors();
    };

    Ext.data.DataReader.prototype = {

        /**
         * Abstract method, overridden in {@link Ext.data.JsonReader}
         */
        buildExtractors : Ext.emptyFn,

        /**
         * Used for un-phantoming a record after a successful database insert.  Sets the records pk along with new data from server.
         * You must return at least the database pk using the idProperty defined in your DataReader configuration.  The incoming
         * data from server will be merged with the data in the local record.
         * In addition, you must return record-data from the server in the same order received.
         * Will perform a commit as well, un-marking dirty-fields.  Store's "update" event will be suppressed.
         * @param {Record/Record[]} record The phantom record to be realized.
         * @param {Object/Object[]} data The new record data to apply.  Must include the primary-key from database defined in idProperty field.
         */
        realize: function(rs, data){
            if (Ext.isArray(rs)) {
                for (var i = rs.length - 1; i >= 0; i--) {
                    // recurse
                    if (Ext.isArray(data)) {
                        this.realize(rs.splice(i,1).shift(), data.splice(i,1).shift());
                    }
                    else {
                        // weird...rs is an array but data isn't??  recurse but just send in the whole invalid data object.
                        // the else clause below will detect !this.isData and throw exception.
                        this.realize(rs.splice(i,1).shift(), data);
                    }
                }
            }
            else {
                // If rs is NOT an array but data IS, see if data contains just 1 record.  If so extract it and carry on.
                if (Ext.isArray(data) && data.length == 1) {
                    data = data.shift();
                }
                if (!this.isData(data)) {
                    // TODO: Let exception-handler choose to commit or not rather than blindly rs.commit() here.
                    //rs.commit();
                    throw new Ext.data.DataReader.Error('realize', rs);
                }
                var values = this.extractValues(data, rs.fields.items, rs.fields.items.length);
                rs.phantom = false; // <-- That's what it's all about
                rs._phid = rs.id;  // <-- copy phantom-id -> _phid, so we can remap in Store#onCreateRecords
                rs.id = data[this.meta.idProperty];
                rs.data = values;
                rs.commit();
            }
        },

        /**
         * Used for updating a non-phantom or "real" record's data with fresh data from server after remote-save.
         * If returning data from multiple-records after a batch-update, you must return record-data from the server in
         * the same order received.  Will perform a commit as well, un-marking dirty-fields.  Store's "update" event will be
         * suppressed as the record receives fresh new data-hash
         * @param {Record/Record[]} rs
         * @param {Object/Object[]} data
         */
        update : function(rs, data) {
            if (Ext.isArray(rs)) {
                for (var i=rs.length-1; i >= 0; i--) {
                    if (Ext.isArray(data)) {
                        this.update(rs.splice(i,1).shift(), data.splice(i,1).shift());
                    }
                    else {
                        // weird...rs is an array but data isn't??  recurse but just send in the whole data object.
                        // the else clause below will detect !this.isData and throw exception.
                        this.update(rs.splice(i,1).shift(), data);
                    }
                }
            }
            else {
                // If rs is NOT an array but data IS, see if data contains just 1 record.  If so extract it and carry on.
                if (Ext.isArray(data) && data.length == 1) {
                    data = data.shift();
                }
                if (this.isData(data)) {
                    rs.data = this.extractValues(Ext.apply(rs.data, data), rs.fields.items, rs.fields.items.length);
                }
                rs.commit();
            }
        },

        /**
         * Returns true if the supplied data-hash looks and quacks like data.  Checks to see if it has a key
         * corresponding to idProperty defined in your DataReader config containing non-empty pk.
         * @param {Object} data
         * @return {Boolean}
         */
        isData : function(data) {
            return (data && Ext.isObject(data) && !Ext.isEmpty(data[this.meta.idProperty])) ? true : false;
        }
    };

    /**
     * @class Ext.data.DataReader.Error
     * @extends Ext.Error
     * General error class for Ext.data.DataReader
     */
    Ext.data.DataReader.Error = Ext.extend(Ext.Error, {
        constructor : function(message, arg) {
            this.arg = arg;
            Ext.Error.call(this, message);
        },
        name: 'Ext.data.DataReader'
    });
    Ext.apply(Ext.data.DataReader.Error.prototype, {
        lang : {
            'update': "#update received invalid data from server.  Please see docs for DataReader#update and review your DataReader configuration.",
            'realize': "#realize was called with invalid remote-data.  Please see the docs for DataReader#realize and review your DataReader configuration.",
            'invalid-response': "#readResponse received an invalid response from the server."
        }
    });