How to modify data after load and before save in store?

I want to add some properties to all records after they are loaded from server.

Code:

Ext.define('Dms.proxy.CustomRestProxy', {


    alias: 'proxy.customRest',


    extend: 'Ext.data.proxy.Rest',


    afterRequest: function(request, success) {
        var records = request.getRecords();
        var jsonData = request.getJsonData();


        request.setRecords(records);
        request.setJsonData(jsonData);
    }
});

Ext.define('DocItemTree', {
    extend: 'Ext.data.Model',


    idProperty: 'Id',


    fields: [
        { name: 'Id', type: 'string' },
        { name: 'Name', type: 'string' }
    ],


    proxy: {
        type: 'customRest',
        url: '/api-ci/DocItemTree',
        // Use extra parameter to get only items which are corresponding to actual entity
        extraParams: {
            Entity: Dms.config.Runtime.getEntityFromUrl(),
            EntityType: Dms.config.Runtime.getEntityTypeFromUrl()
        }
    }
});

I have tried it with a custom proxy, but the getRecords() function and the getJsonData() function are returning no data



How to modify data after load and before save in store?