Skip to main content

Hibernate Object States

Hibernate defines and supports the following object states.


Transient - an object is transient if it has just been instantiated using the new operator, and it is not associated with a Hibernate Session. It has no persistent representation in the database and no identifier value has been assigned. Transient instances will be destroyed by the garbage collector if the application doesn't hold a reference anymore. Use the Hibernate Session to make an object persistent (and let Hibernate take care of the SQL statements that need to be executed for this transition.


Persistent - a persistent instance has a representation in the database and an identifier value. It might just have been saved or loaded, however, it is by definition in the scope of a Session. Hibernate will detect any changes made to an object in persistent state and synchronize the state with the database when the unit of work completes. Developers don't execute manual UPDATE statements, or DELETE statements when an object should be made transient.
Detached - a detached instance is an object that has been persistent, but its Session has been closed. The reference to the object is still valid, of course, and the detached instance might even be modified in this state. A detached instance can be reattached to a new Session at a later point in time, making it (and all the modifications) persistent again. This feature enables a programming model for long running units of work that require user think-time. We call them application transactions, i.e. a unit of work from the point of view of the user.
Labels:

Comments

Post a Comment

Popular posts from this blog

Advantages & Disadvantages of Synchronous / Asynchronous Communications?

  Asynchronous Communication Advantages: Requests need not be targeted to specific server. Service need not be available when request is made. No blocking, so resources could be freed.  Could use connectionless protocol Disadvantages: Response times are unpredictable. Error handling usually more complex.  Usually requires connection-oriented protocol.  Harder to design apps Synchronous Communication Advantages: Easy to program Outcome is known immediately  Error recovery easier (usually)  Better real-time response (usually) Disadvantages: Service must be up and ready. Requestor blocks, held resources are “tied up”.  Usually requires connection-oriented protocol
Post a Comment
Continue Reading >>>>

WebSphere MQ Interview Questions

What is MQ and what does it do? Ans. MQ stands for MESSAGE QUEUEING. WebSphere MQ allows application programs to use message queuing to participate in message-driven processing. Application programs can communicate across different platforms by using the appropriate message queuing software products. What is Message driven process? Ans . When messages arrive on a queue, they can automatically start an application using triggering. If necessary, the applications can be stopped when the message (or messages) have been processed. What are advantages of the MQ? Ans. 1. Integration. 2. Asynchrony 3. Assured Delivery 4. Scalability. How does it support the Integration? Ans. Because the MQ is independent of the Operating System you use i.e. it may be Windows, Solaris,AIX.It is independent of the protocol (i.e. TCP/IP, LU6.2, SNA, NetBIOS, UDP).It is not required that both the sender and receiver should be running on the same platform What is Asynchrony? Ans. With messag
11 comments
Continue Reading >>>>

XML Binding with JAXB 2.0 - Tutorial

Java Architecture for XML Binding (JAXB) is an API/framework that binds XML schema to Java representations. Java objects may then subsequently be used to marshal or unmarshal XML documents. Marshalling an XML document means creating an XML document from Java objects. Unmarshalling means creating creating a Java representation of an XML document (or, in effect, the reverse of marshaling). You retrieve the element and attribute values of the XML document from the Java representation. The JAXB 2.0 specification is implemented in JWSDP 2.0. JAXB 2.0 has some new features, which facilitate the marshalling and unmarshalling of an XML document. JAXB 2.0 also allows you to map a Java object to an XML document or an XML Schema. Some of the new features in JAXB 2.0 include: Smaller runtime libraries are required for JAXB 2.0, which require lesser runtime memory. Significantly, fewer Java classes are generated from a schema, compared to JAXB 1.0. For each top-level complexType, 2.0 generates a v
Post a Comment
Continue Reading >>>>