[SalesForce] Lightning -> Parent component retreive values from child components

Bob you've probably addressed this already but facing a similar problem, I have had success using the component.getReference() method rather than component.get() to set attribute values on dynamically created components. So instead of:

swapInThree : function(component, event, helper) {
    var acc=component.get("v.acc");
    var str=component.get("v.str");

you could try:

swapInThree : function(component, event, helper) {
    var acc=component.getReference("v.acc");
    var str=component.getReference("v.str");

I think that after spending few hours I found the answer for the above. Still not sure if it's a bug or a feature of the framework, but definately it has something to do with how secure objects are constructed.

You need to make sure all possible properties for the object are defined (even if null) when you call component.set("v.obj", obj); for the first time.

Here is example component & controller, with one simple attribute (initialized on init), and two buttons calling log & set functions of controller:

<aura:component >
    <aura:attribute name="testAtr" type="Object" access="global"/>
    <aura:handler name="init" value="{!this}" action="{!c.initialize}"/>
    <p><a onclick="{!c.logAtr}">Console Log Parent</a></p>
    <p><a onclick="{!c.setSth}">Set Something</a></p>
</aura:component>

({
    initialize : function(component, event, helper) {
        var obj = {};
        obj.data = 'test';
        // obj.someNewProperty = null;
        component.set("v.testAtr", obj);
    },
    logAtr : function(component, event, helper) {
        console.log(component.get("v.testAtr.someNewProperty"));
    },
    setSth : function(component, event, helper) {
        var testAtr = component.get("v.testAtr");
        testAtr.someNewProperty = 'New Property';
        component.set("v.testAtr", testAtr);
    },
})

If the line obj.someNewProperty = null; in initialize method is commented out, console.log returns undefined even if you call setSth method that actually sets value of obj.someNewProperty.

If the line obj.someNewProperty = null; in initialize method is present, console.log returns null before calling setSth method and 'New Property' after calling it.

EDIT: But this has some drawbacks. Let's imagine we have a simple form for sObject. You need to initialize object with all the possible properties. If you don't do this - no values will be kept. If these lines: acc.Name = null; acc.Phone = null; acc.Account_Status__c = null; are commented as in below example - value put in the input text is not bind to testAcc attribute.

<aura:component >
    <aura:attribute name="testAcc" type="Account" access="global"/>
    <aura:handler name="init" value="{!this}" action="{!c.initialize}"/>

    <p>Name: <ui:inputText value="{!v.testAcc.Name}"/></p>
    <p>Phone: <ui:inputText value="{!v.testAcc.Phone}"/></p>
    <p>Status: <ui:inputText value="{!v.testAcc.Account_Status__c}"/></p>
    <p><a onclick="{!c.logAcc}">Console Log Acc</a></p>
</aura:component>

({
    initialize : function(component, event, helper) {
        var acc = {};
        // acc.Name = null;
        // acc.Phone = null;
        // acc.Account_Status__c = null;
        component.set("v.testAcc", acc);
    },

    logAcc : function(component) {
        console.log(component.get("v.testAcc"));
    }
})