Is it possible to get related ExtJs 6 data not by idProperty?

Question

ExtJS/Sencha

Good time of the day!
I started developing a new application on ExtJs 6, and again faced with the fact that there are irreparable changes in the API (compared to version 5, and even more so 4). I've read all the change logs and found nothing.

1. The documentation constantly imposes getting links in models through the declaration of the reference property, in Ext.data.field.Field. The documentation directly says that the connection will be received through the field specified in idProperty. Description ManyToOne sends back, foreignKey property cut out. How to get related models using a field other than idProperty?
   
2. Similar question, only about associationKey? Where is it now configured and how?