Session in ATG

Question

Hi,
  For what functionality session is used in ATG, i.e what is the use of session in ATG. and how is it achieved in ATG????
Components : session scoped
Repository : Transient properties  
Session cookies: ????
Regards

Answer 1

Repository transient properties are session scoped . the values stored in Transient Properties are available only till a particular session exists. Once the session has expired all the transient properties values will be gone.
When and why are transient properties should be used.???
Why cant we use HttpSession session=session = request.getSession(true); instead of transient properties????
By default the transient property values are not stored in session but stored in the repository item level caches. Even if you disable the caching for an item, ATG internally caches its property values during a transaction.
We access repository properties through RepositoryItem object instances and for any given item-descriptor in a repository there can be many RepositoryItem objects each having its own state (property values). So same property (transient or persistent) can have same or different value as the RepositoryItem object instance is going to be different. Now imagine if a transient property value was stored in session then how it would handle the different values for a given transient property for different items within a same session unless that property holds something session specific.
Having said this you must also know that there are couple of custom property descriptor classes provided OOTB: atg.repository.SessionPropertyDescriptor and atg.repository.SessionEnumPropertyDescriptor each of which uses HttpSession to store property values. So if your transient property is declared with the property-type attribute specifying any of these custom property descriptor classes then only that property value would be stored as a session attribute. Also note that you would have to pass the session attribute name from your repository definition something like below:
<item-descriptor name="myItem" ...>
  <property name="myProperty" data-type="string" property-type="atg.repository.SessionPropertyDescriptor" ...>
    <attribute name="sessionAttributeName" value="myProp"/>
  </property>
</item-descriptor>
I don't remember exactly from which version but SessionPropertyDescriptor has now been deprecated so if you plan to use it you have to do it at your own risk. The other class SessionEnumPropertyDescriptor can be used only for enumerated proeprties and is used in the securityStatus property of user profile. Refer this
Oracle ATG Web Commerce - Security Status
Does cookie play a role in ATG for maintaining session.   Profile and Order data is stored in cookies right???
Whenever a request comes in without a session-id in the cookie or in the URL, the application server would create a new session for the particular web-app that is being requested. And like any typical web-app ATG also uses cookies to recognize a returning user. ATG uses cookies for different scenarios like identifying anonymous users on subsequent visits, auto-login for registered users, if a user is automatically logged in and if there were any items in his cart in the previous visit then load them back to the current cart etc. Of course there some configuration changes required to get these scenarios working in ATG.
Remember cookies can be blocked or deleted by the user so why would you store any important data in them? Cookies store a small piece of information (usually an id) which browser can send to the server with every request and they do not hold any explicit profile or order data.
Hope it helps and clarifies your concerns.