Interacting with legacy Has One associations in Extjs 5.1.1 - extjs

Question

I had to upgrade from 4.1.2 to 5.1.1 for the sole sake of widget columns. I'm having trouble getting hasone associations to work.
I've got a model that looks like this:
Ext.define('PP.model.LM.FOOModel', {
extend: 'Ext.data.Model',
requires: [
'Ext.data.field.Field'
],
fields: [
{
name: 'ID'
},
//Boatload of simple fields
],
hasOne: {
model: 'PP.model.LM.FOO1Model',
name: 'FOO1',
associationKey: 'FOO1'
}
});
When I interact with the model, there is no getter \ setter methods, and FOO1Model's data is only present as an object that can be accessed by
record.get('FOO1');
Could someone please point out what exactly am I doing wrong?
I tried doing it with the new approach - creating a field with a reference to the desired model. It works fine when I call setFoo1, and then do a get. But.
When I make an Ajax request, and try reading received JSON using Ext.data.reader.Json, it seems to fail to understand that a certain property in the object is in fact an associated model. The data in Foo1 appears in the model as an object in Foo1 property. The reqest returns an array of models that have many FooModels.
The Json looks like this:
{
"root": [{
"ID": 4241,
"Foos": [{
ID: 2237,
"Foo1": {
"ID": 1216
}
}]
}],
"success": true
}

Answer 1

It seems that hasOne doesn't exist in ExtJS 5.1 it is now done like this:
fields: [{
name: 'addressId',
reference: 'Address',
unique: true
}]
Check Model api for more info.

Answer 2

Had to debug the Ext.data.reader.Json to understand. The key was passing associationKey in reference config. Unless it's specified the reader will assume that the data for the association resides under '_foo1' field in JSON.
Is it mentioned anywhere in sencha docs? I don't think so. Am I supposed to feel like an imbecile for not guessing that?
Sample for unfortunate poor sods like me, who might encounter the problem in future:
{
name: 'Foo1',
reference: {
type: 'FOO1Model',
association: 'Foo1',
associationKey: 'Foo1'
},
unique: true
}