1. Professional Open Source™
Conversations
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2. Session Per Request
Professional Open Source™
 The scope of the persistence context is often the same scope
 as the database transaction. This is also known as session-per-
request .
See the example in conversation project
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3. What is Conversation ?
Professional Open Source™
 Conversations are units of work that span user think-time.
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4. Propagation through thread-local
Professional Open Source™
 If sessionFactory.getCurrentSession() is called for the first time in the
current Java thread, a new Session is opened and returned—you get
a fresh persistence context.
 You can immediately begin a database transaction on this new
Session, with the Hibernate Transaction interface
 All the data-access code that calls getCurrentSession() on the global
shared SessionFactory gets access to the same current Session—if
it’s called in the same thread. The unit of work completes when the
Transaction is committed (or rolled back). Hibernate also flushes
and closes the current Session and its persistence context if you
commit or roll back the transaction.
 U should not close the session explicitly.
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5. Binding session to thread
Professional Open Source™
 Internally, Hibernate binds the current Session to the currently
running Java thread.
 In the Hibernate community, this is also known as the ThreadLocal
Session pattern.
 You have to enable this binding in your Hibernate configuration by
setting as follows :
 hibernate.current_session_context_class = thread.
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6. Propagation with JTA
Professional Open Source™
 The current Session is bound automatically to the current JTA system
transaction.
 When the transaction completes, either through commit or rollback,
the persistence context is flushed and the internally bound current
Session is closed.
 You have to enable this binding in your Hibernate configuration by
setting as follows :
 hibernate.current_session_context_class = jta
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7. Conversations with detached objects
Professional Open Source™
 Let us assume a conversation that has two steps: The first step loads
an object, and the second step makes changes to the loaded object
persistent.
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8. How is isolation guaranteed in this strategy ?
Professional Open Source™
 Isolation is guaranteed with optimistic locking.
 So, U need to enable Hibernate’s automatic versioning for all
persistent classes.
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9. How can u make the conversation atomic?
Professional Open Source™
 One solution is to not flush the persistence contexts on commit—that
is, to set a FlushMode.MANUAL on a Session that isn’t supposed to
persist modifications
 Another option is to use compensation actions that undo any step
that made permanent changes, and to call the appropriate
compensation actions when the user aborts the conversation. But this
requires a lot of work from the application developer
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10. Extending a Session for a conversation
Professional Open Source™
 The Hibernate Session has an internal persistence context. You can
implement a conversation that doesn’t involve detached objects by
extending the persistence context to span the whole conversation.
This is known as the session-per-conversation strategy, as shown
below :
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11. Extending a Session for a conversation
Professional Open Source™
 A new Session and persistence context are opened at the beginning
of a conversation.
 The Session is automatically disconnected from the underlying
 JDBC Connection as soon as you commit the database transaction.
 You can now hold on to this disconnected Session and its internal
persistence context during user think-time. As soon as the user
continues in the conversation and executes the next step, you
reconnect the Session to a fresh JDBC Connection by beginning
 a second database transaction.
 Any object that has been loaded in this conversation is in persistent
state: It’s never detached. Hence, all modifications you made to any
persistent object are flushed to the database as soon as you call
 flush() on the Session.
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12. Delaying insertion until flush-time
Professional Open Source™
 The save() method on the Session requires that the new database
identifier of the saved instance must be returned. So, the identifier
value has to be generated when the save() method is called. This is
no problem with most identifier generator strategies; for example,
Hibernate can call a sequence, do the in-memory increment, or ask
the hilo generator for a new value. Hibernate doesn’t have to execute
an SQL INSERT to return the identifier value on save() and assign it
to the now-persistent instance.
 The exceptions are identifier-generation strategies that are triggered
after the INSERT occurs. One of them is identity, the other is select;
both require that a row is inserted first. If you map a persistent class
with these identifier generators, an immediate INSERT is executed
when you call save()!
 So, we should avoid these identifier generation strategies .If we use,
we have to write the compensation actions when we rollback the
conversation .
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13. How to rollback a conversation ???
Professional Open Source™
 As we have enabled FlushMode.MANUAL , the changes made to
the persistent objects will not cause any DML statements until we
flush the session .
 Simply close the session with out flushing it. So, the changes made to
the persistent objects in this session will not be propagated to the
database.
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14. Managing the current Session
Professional Open Source™
 You have to enable the following setting :
 hibernate.current_session_context_class = managed.
 The Hibernate built-in implementation you just enabled is called
managed because it delegates the responsibility for managing the
scope, the start and end of the current Session, to you. You manage
the scope of the Session with three static methods:
 public class ManagedSessionContext implements
CurrentSessionContext {
 public static Session bind(Session session) { ... }
 public static Session unbind(SessionFactory factory) { ... }
 public static boolean hasBind(SessionFactory factory) { ... }
}
 U must write ur own interceptor or filter for this .
 See the example….
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