I'm quite new to sencha touch and trying to figure out how to use select form fields with composite models. I have two stores for entities A and B. With A having a field of type B.

Ext.regModel('A', { 
    fields: [ 
        { name: "b", type: "B" }
The final goal is to use a select field to display all entities of B from the (B-)store as choices and set the selected entity on A. I'm currently at a loss how to accomplish this. It sure seems like a pretty basic and common problem, but I can't find the proper way to configure the select field...

items: [{
    xtype: 'selectfield',
    name: 'b',
    store: 'bStore',
    displayField: 'name' // a property of B
    // valueField: accepts only String/Integer, how do I return the "whole" selected (B-)entity?
Thanks for any input/pointers on the proper way to do something like this...