title: How to make an IntegerField/CharField be auto-incrementing field in Django as 1000001, 1000002
body: <p>I have a field "CharField" in a model, when user create a project, how to make a IntegerField/CharField be an default auto-incrementing field in Django as 1000001, 1000002? or <code>year</code> + 00001, 00002, 0003 etc, I cannot have more than one AutoField, and the field already has much data.</p>