Hibernate Interview Questions And Answers - DoAnswers.com

Hibernate's primary feature is mapping from Java classes to database tables (and from Java data types to SQL data types). Hibernate also provides data query and retrieval facilities. Hibernate generates the SQL calls and relieves the developer from manual result set handling and object conversion, keeping the application portable to all SQL databases, with database portability delivered at very little performance overhead.

Hibernate provides transparent persistence for Plain Old Java Objects (POJOs). The only strict requirement for a persistent class is a no-argument constructor, not compulsorily public. (Proper behavior in some applications also requires special attention to the equals() and hashCode() methods.)

Hibernate provides a dirty checking feature that avoids unnecessary database write actions by performing SQL updates only on the modified fields of persistent objects.

Hibernate can be used both in standalone Java applications and in Java EE applications using servlets or EJB session beans.

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.

Those are .1 to many, many to many, many to one.. relations.

These relational mappings are done by using the hibernates utilities such as list, set, bags, object...

1. Get java.sql.Connection from Hibernate Session and then play with that connection by call callablestatement.

Connection con = null;

try {
con = session.connection();

CallableStatement st = con
.prepareCall("{call your_sp(?,?)}");
st.registerOutParameter(2, Types.INTEGER);
st.setString(1, "some_Seq");

st.executeUpdate();

3. By this process you can write hibernate procedure:

< sql-query name="selectAllEmployees_SP" callable="true">

{ ? = call selectAllEmployees() }

4. You can declare it as Named queries in one of your mapping files and give unique name.

Call it in your code. Sample code is below.

SQLQuery sq = (SQLQuery) session.getNamedQuery("findSearchResultsListSP");

sq.addEntity("documentTypeCode", documentTypeCode);

List results = sq.list();

10. What are the different approaches to represent an inheritance hierarchy?