When an entity instance of an immutable class is made persistent, Hibernate automatically makes it read-only.

An entity of an immutable class can created and deleted the same as an entity of a mutable class.

Hibernate treats a persistent entity of an immutable class the same way as a read-only persistent entity of a mutable class. The only exception is that Hibernate will not allow an entity of an immutable class to be changed so it is not read-only.

To change the default behavior so Hibernate loads entity instances of mutable classes into the session and automatically makes them read-only, call:

Session.setDefaultReadOnly( true );

To change the default back so entities loaded by Hibernate are not made read-only, call:

Session.setDefaultReadOnly( false );

You can determine the current setting by calling:

Session.isDefaultReadOnly();

If Session.isDefaultReadOnly() returns true, entities loaded by the following are automatically made read-only:

If Session.isDefaultReadOnly() returns false (the default) when an HQL query or criteria executes, then entities and proxies of mutable classes loaded by the query will not be read-only.

You can override this behavior so that entities and proxies loaded by an HQL query or criteria are automatically made read-only.

For an HQL query, call:

Query.setReadOnly( true );

Query.setReadOnly( true ) must be called before Query.list(), Query.uniqueResult(), Query.scroll(), or Query.iterate()

For an HQL criteria, call:

Criteria.setReadOnly( true );

Criteria.setReadOnly( true ) must be called before Criteria.list(), Criteria.uniqueResult(), or Criteria.scroll()

Entities and proxies that exist in the session before being returned by an HQL query or criteria are not affected.

Uninitialized persistent collections returned by the query are not affected. Later, when the collection is initialized, entities loaded into the session will be read-only if Session.isDefaultReadOnly() returns true.

Using Query.setReadOnly( true ) or Criteria.setReadOnly( true ) works well when a single HQL query or criteria loads all the entities and intializes all the proxies and collections that the application needs to be read-only.

When it is not possible to load and initialize all necessary entities in a single query or criteria, you can temporarily change the session default to load entities as read-only before the query is executed. Then you can explicitly initialize proxies and collections before restoring the session default.

Session session = factory.openSession();
Transaction tx = session.beginTransaction();
 
setDefaultReadOnly( true );
Contract contract = 
   ( Contract ) session.createQuery(
           "from Contract where customerName = 'Sherman'" )
           .uniqueResult();
Hibernate.initialize( contract.getPlan() );
Hibernate.initialize( contract.getVariations() );
Hibernate.initialize( contract.getNotes() );
setDefaultReadOnly( false );
...
tx.commit();
session.close();

If Session.isDefaultReadOnly() returns true, then you can use Query.setReadOnly( false ) and Criteria.setReadOnly( false ) to override this session setting and load entities that are not read-only.

To make a persistent entity or proxy read-only, call:

Session.setReadOnly(entityOrProxy, true)

To change a read-only entity or proxy of a mutable class so it is no longer read-only, call:

Session.setReadOnly(entityOrProxy, false)

To throw away non-flushed changes and make the persistent entity consistent with its database representation, call:

session.refresh( entity );

To flush changes made before or while the entity was read-only and make the database representation consistent with the current state of the persistent entity:

// evict the read-only entity so it is detached
session.evict( entity );

// make the detached entity (with the non-flushed changes) persistent
session.update( entity );

// now entity is no longer read-only and its changes can be flushed
s.flush();

When a persistent object is read-only, Hibernate does not dirty-check simple properties.

Hibernate will not synchronize simple property state changes to the database. If you have automatic versioning, Hibernate will not increment the version if any simple properties change.

Session session = factory.openSession();
Transaction tx = session.beginTransaction();

// get a contract and make it read-only
Contract contract = ( Contract ) session.get( Contract.class, contractId );
session.setReadOnly( contract, true );

// contract.getCustomerName() is "Sherman"
contract.setCustomerName( "Yogi" );
tx.commit();

tx = session.beginTransaction();

contract = ( Contract ) session.get( Contract.class, contractId );
// contract.getCustomerName() is still "Sherman"
...
tx.commit();
session.close();