Experimental Feature - Freeze and detach beans (and attach)

[rbygrave]

• Frozen beans as ReadOnly + Unmodifiable collections

• Add Transaction.freezeAndDetach() returning FrozenBeans

• Add Transaction.attach( FrozenBeans )

• InterceptReadOnly now supports lazy loading

• Query.setReadOnly(true) now uses InterceptReadOnly [when it used to ALSO require Query.setDisableLazyLoading(true)}

• Add EntityBeanIntercept.errorOnLazyLoad (such that lazy loading on frozen bean is an error)

• BeanList, BeanSet, BeanMap are now freezable

• ModifyAwareList Set and Map are now freezable

• Adds FrozenBeans [marker] interface for the frozen and detached beans [which can then be attached to other transactions and used as cached/frozen beans to seed the persistence context]

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Expected use case

For performance reasons as a "caching mechanism" where there is good value in using unmodifable beans with potentially a significant amount of relationships and related data that is all infrequently changing.

These beans that are cached and used will often be graphs of related objects and represent some relatively infrequently changing "meta data".

Building frozen beans - freezeAndDetach()

  private FrozenBeans buildFrozenBeans() {
     try (Transaction txn = DB.beginTransaction()) {

       List<Customer> list = DB.find(Customer.class)
         .setReadOnly(true)
         .orderBy("id")
         .setMaxRows(3)
         .findList();

       // perform some lazy loading if we desire
       for (Customer customer : list) {
         customer.getContacts().size();
         Address billingAddress = customer.getBillingAddress();
         if (billingAddress != null) {
           Country country = billingAddress.getCountry();
           if (country != null) {
             country.getName();
           }
         }
       }

       return txn.freezeAndDetach();
     }
   }

Using frozen beans - attach()

  FrozenBeans frozenBeans = ...;

  try (Transaction txn = DB.beginTransaction()) {

    txn.attach(frozenBeans);

    List<Order> orders = DB.find(Order.class)
        .findList();
   ...
}