In EXT JS 4 there still is a chance to pass only the fields and data directly to the DataStore when you construct it, instead of passing a model. Ext JS is then creating an internal model from the fields passed. Now, the problem is that Ext JS is going to append an identifier field ‘id’, if there is no field given with that name. If our identifier field has other name, like ‘customID’, then it causes a lot of trouble when it comes to getting the record with a given identifier (getById). Unfortunately there is no way to specify which field we’d like to use as identifier in this case.