1. What is ORM ?

ORM stands for object/relational mapping. ORM is the automated persistence of objects in a Java
application to the tables in a relational database.

2. What does ORM consists of ?

An ORM solution consists of the followig four pieces:

 API for performing basic CRUD operations

 API to express queries refering to classes
 Facilities to specify metadata
 Optimization facilities : dirty checking,lazy associations fetching

3. What are the ORM levels ?

The ORM levels are:

 Pure relational (stored procedure.)

 Light objects mapping (JDBC)
 Medium object mapping
 Full object Mapping (composition,inheritance, polymorphism, persistence by reachability)

4. What is Hibernate?
Hibernate is a pure Java object-relational mapping (ORM) and persistence framework that allows you to
map plain old Java objects to relational database tables using (XML) configuration files.Its purpose is to
relieve the developer from a significant amount of relational data persistence-related programming
tasks.

5. Why do you need ORM tools like hibernate?

The main advantage of ORM like hibernate is that it shields developers from messy SQL. Apart from
this, ORM provides following benefits:

 Improved productivity
o High-level object-oriented API
o Less Java code to write
o No SQL to write
 Improved performance
o Sophisticated caching
o Lazy loading
o Eager loading
 Improved maintainability
o A lot less code to write
 Improved portability
o ORM framework generates database-specific SQL for you

6.What Does Hibernate Simplify?

Hibernate simplifies:

Saving and retrieving your domain objects

Making database column and table name changes
Centralizing pre save and post retrieve logic
Complex joins for retrieving related items

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 Schema creation from object model

7.What is the need for Hibernate xml mapping file?

Hibernate mapping file tells Hibernate which tables and columns to use to load and store objects.
Typical mapping file look as follows:

8.What are the most common methods of Hibernate configuration?

The most common methods of Hibernate configuration are:

 Programmatic configuration
 XML configuration (hibernate.cfg.xml)

9.What are the important tags of hibernate.cfg.xml?

Following are the important tags of hibernate.cfg.xml:

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10. What are the Core interfaces are of Hibernate framework?

The five core interfaces are used in just about every Hibernate application. Using these
interfaces, you can store and retrieve persistent objects and control transactions.

 Session interface
 SessionFactory interface
 Configuration interface
 Transaction interface
 Query and Criteria interfaces

11.What role does the Session interface play in Hibernate?

The Session interface is the primary interface used by Hibernate applications. It is a single-
threaded, short-lived object representing a conversation between the application and the
persistent store. It allows you to create query objects to retrieve persistent objects.

Session session = sessionFactory.openSession();

Session interface role:

 Wraps a JDBC connection

 Factory for Transaction
 Holds a mandatory (first-level) cache of persistent objects, used when navigating the
object graph or looking up objects by identifier

 12.What role does the SessionFactory interface play in Hibernate?

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  The application obtains Session instances from a SessionFactory. There is typically a
single SessionFactory for the whole application—created during application
initialization. The SessionFactory caches generate SQL statements and other mapping
metadata that Hibernate uses at runtime. It also holds cached data that has been read
in one unit of work and may be reused in a future unit of work

SessionFactory sessionFactory = configuration.buildSessionFactory();

13. What is the general flow of Hibernate communication with RDBMS?

The general flow of Hibernate communication with RDBMS is :

 Load the Hibernate configuration file and create configuration object. It will
automatically load all hbm mapping files
 Create session factory from configuration object
 Get one session from this session factory
 Create HQL Query
 Execute query to get list containing Java objects

14. What is Hibernate Query Language (HQL)?

Hibernate offers a query language that embodies a very powerful and flexible mechanism to
query, store, update, and retrieve objects from a database. This language, the Hibernate
query Language (HQL), is an object-oriented extension to SQL.

15. How do you map Java Objects with Database tables?

 First we need to write Java domain objects (beans with setter and getter).
 Write hbm.xml, where we map java class to table and database columns to Java class
variables.

Example :
<hibernate-mapping>
  <class name="com.test.User"  table="user">
   <property  column="USER_NAME" length="255"
      name="userName" not-null="true"  type="java.lang.String"/>
   <property  column="USER_PASSWORD" length="255"
name="userPassword" not-null="true"  type="java.lang.String"/>
 </class>
</hibernate-mapping>

16.What’s the difference between load() and get()?

load() vs. get() :-

load()  get() 

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 If you are not sure that the object
Only use the load() method if you are sure
exists, then use one of the get()
that the object exists. 
methods. 

load() method will throw an exception if the get() method will return null if the
unique id is not found in the database.  unique id is not found in the database. 

load() just returns a proxy by default and

get() will hit the database
database won’t be hit until the proxy is first
immediately. 
invoked.  

17.What is the difference between and merge and update ?

Use update() if you are sure that the session does not contain an already persistent instance
with the same identifier, and merge() if you want to merge your modifications at any time
without consideration of the state of the session.

18.How do you define sequence generated primary key in hibernate?

Using <generator> tag.
Example:-
<id column="USER_ID" name="id" type="java.lang.Long">
<generator class="sequence">
<param name="table">SEQUENCE_NAME</param>
  <generator>
</id>

19.Define cascade and inverse option in one-many mapping?

cascade - enable operations to cascade to child entities.
cascade="all|none|save-update|delete|all-delete-orphan"

inverse - mark this collection as the "inverse" end of a bidirectional association.

inverse="true|false"
Essentially "inverse" indicates which end of a relationship should be ignored, so when
persisting a parent who has a collection of children, should you ask the parent for its list of
children, or ask the children who the parents are?

20.What do you mean by Named – SQL query?

Named SQL queries are defined in the mapping xml document and called wherever required.
Example:
<sql-query name = "empdetails">
   <return alias="emp" class="com.test.Employee"/>
      SELECT emp.EMP_ID AS {emp.empid},
                 emp.EMP_ADDRESS AS {emp.address},
                 emp.EMP_NAME AS {emp.name}

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 FROM Employee EMP WHERE emp.NAME LIKE :name
</sql-query>

Invoke Named Query :

List people = session.getNamedQuery("empdetails")

.setString("TomBrady", name)
.setMaxResults(50)
.list();

21.How do you invoke Stored Procedures?

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

<return alias="emp" class="employee">
  <return-property name="empid" column="EMP_ID"/>       

<return-property name="name" column="EMP_NAME"/>       

<return-property name="address" column="EMP_ADDRESS"/>
    { ? = call selectAllEmployees() }
</return>
</sql-query>

22.Explain Criteria API

Criteria is a simplified API for retrieving entities by composing Criterion objects. This is a very
convenient approach for functionality like "search" screens where there is a variable number
of conditions to be placed upon the result set.
Example :
List employees = session.createCriteria(Employee.class)
       .add(Restrictions.like("name", "a%") )
         .add(Restrictions.like("address", "Boston"))
.addOrder(Order.asc("name") )
.list();

23.Define HibernateTemplate?

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org.springframework.orm.hibernate.HibernateTemplate is a helper class which provides
different methods for querying/retrieving data from the database. It also converts checked
HibernateExceptions into unchecked DataAccessExceptions.

24.What are the benefits does HibernateTemplate provide?

The benefits of HibernateTemplate are :

 HibernateTemplate, a Spring Template class simplifies interactions with Hibernate

Session.
 Common functions are simplified to single method calls.
 Sessions are automatically closed.
 Exceptions are automatically caught and converted to runtime exceptions.
 25.How do you switch between relational databases without code changes?
 Using Hibernate SQL Dialects , we can switch databases. Hibernate will generate
appropriate hql queries based on the dialect defined.

26.If you want to see the Hibernate generated SQL statements on console, what
should we do?
 In Hibernate configuration file set as follows:
<property name="show_sql">true</property>

27.What are derived properties?
 The properties that are not mapped to a column, but calculated at runtime by
evaluation of an expression are called derived properties. The expression can be
defined using the formula attribute of the element.

28.What is component mapping in Hibernate?

 A component is an object saved as a value, not as a reference

 A component can be saved directly without needing to declare interfaces or identifier
properties
 Required to define an empty constructor
 Shared references not supported
 Example:

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 

29.What is the difference between sorted and ordered collection in hibernate?

 sorted collection vs. order collection :-

sorted collection  order collection 

A sorted collection is sorting a collection by
utilizing the sorting features provided by
Order collection is sorting a collection by
the Java collections framework. The sorting
specifying the order-by clause for sorting
occurs in the memory of JVM which running
this collection when retrieval. 
Hibernate, after the data being read from
database using java comparator. 

If your collection is not large, it will be If your collection is very large, it will be
more efficient way to sort it.  more efficient way to sort it . 
31.What is the advantage of Hibernate over jdbc?
Hibernate Vs. JDBC :-

JDBC  Hibernate 
With JDBC, developer has to write code to Hibernate is flexible and powerful ORM
map an object model's data representation solution to map Java classes to database
to a relational data model and its tables. Hibernate itself takes care of this
corresponding database schema.   mapping using XML files so developer does

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 not need to write code for this. 

Hibernate provides transparent persistence

With JDBC, the automatic mapping of Java
and developer does not need to write code
objects with database tables and vice versa
explicitly to map database tables tuples to
conversion is to be taken care of by the
application objects during interaction with
developer manually with lines of code.  
RDBMS.  

Hibernate provides a powerful query

language Hibernate Query Language
JDBC supports only native Structured Query (independent from type of database) that is
Language (SQL). Developer has to find out expressed in a familiar SQL like syntax and
the efficient way to access database, i.e. includes full support for polymorphic
to select effective query from a number of queries. Hibernate also supports native SQL
queries to perform same task.   statements. It also selects an effective way
to perform a database manipulation task
for an application.  

Application using JDBC to handle persistent

data (database tables) having database
specific code in large amount. The code Hibernate provides this mapping itself. The
written to map table data to application actual mapping between tables and
objects and vice versa is actually to map application objects is done in XML files. If
table fields to object properties. As table there is change in Database or in any table
changed or database changed then it’s then the only need to change XML file
essential to change object structure as well properties.  
as to change code written to map table-to-
object/object-to-table. 

Hibernate reduces lines of code by

With JDBC, it is developer’s responsibility
maintaining object-table mapping itself and
to handle JDBC result set and convert it to
returns result to application in form of Java
Java objects through code to use this
objects. It relieves programmer from
persistent data in application. So with
manual handling of persistent data, hence
JDBC, mapping between Java objects and
reducing the development time and
database tables is done manually.  
maintenance cost.  

Hibernate, with Transparent Persistence,

cache is set to application work space.
Relational tuples are moved to this cache
as a result of query. It improves
With JDBC, caching is maintained by hand- performance if client application reads
coding.   same data many times for same write.
Automatic Transparent Persistence allows
the developer to concentrate more on
business logic rather than this application
code.  

In JDBC there is no check that always every Hibernate enables developer to define
user has updated data. This check has to be version type field to application, due to
added by the developer.   this defined field Hibernate updates version

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 field of database table every time
relational tuple is updated in form of Java
class object to that table. So if two users
retrieve same tuple and then modify it and
one user save this modified tuple to
database, version is automatically updated
for this tuple by Hibernate. When other
user tries to save updated tuple to
database then it does not allow saving it
because this user does not have updated
data.  
32.What are the Collection types in Hibernate ?

 Bag
 Set
 List
 Array
 Map

33.What are the ways to express joins in HQL?

HQL provides four ways of expressing (inner and outer) joins:-

 An implicit association join

 An ordinary join in the FROM clause
 A fetch join in the FROM clause.
 A theta-style join in the WHERE clause.
 34.Define cascade and inverse option in one-many mapping?
 cascade - enable operations to cascade to child entities.
cascade="all|none|save-update|delete|all-delete-orphan"

inverse - mark this collection as the "inverse" end of a bidirectional association.

inverse="true|false"
Essentially "inverse" indicates which end of a relationship should be ignored, so when
persisting a parent who has a collection of children, should you ask the parent for its
list of children, or ask the children who the parents are?

35.What is Hibernate proxy?
 The proxy attribute enables lazy initialization of persistent instances of the class.
Hibernate will initially return CGLIB proxies which implement the named interface.
The actual persistent object will be loaded when a method of the proxy is invoked.

36.How can Hibernate be configured to access an instance variable directly and not
through a setter method ?
By mapping the property with access="field" in Hibernate metadata. This forces hibernate to
bypass the setter method and access the instance variable directly while initializing a newly
loaded object.

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37.How can a whole class be mapped as immutable?

Mark the class as mutable="false" (Default is true),. This specifies that instances of the class
are (not) mutable. Immutable classes, may not be updated or deleted by the application.

38.What is the use of dynamic-insert and dynamic-update attributes in a class mapping?

Criteria is a simplified API for retrieving entities by composing Criterion objects. This is a very
convenient approach for functionality like "search" screens where there is a variable number
of conditions to be placed upon the result set.

 dynamic-update (defaults to false): Specifies that UPDATE SQL should be generated

at runtime and contain only those columns whose values have changed
 dynamic-insert (defaults to false): Specifies that INSERT SQL should be generated
at runtime and contain only the columns whose values are not null.

39.What do you mean by fetching strategy ?

 A fetching strategy is the strategy Hibernate will use for retrieving associated objects
if the application needs to navigate the association. Fetch strategies may be declared
in the O/R mapping metadata, or over-ridden by a particular HQL or Criteria query.
 40.What is automatic dirty checking?
 Automatic dirty checking is a feature that saves us the effort of explicitly asking
Hibernate to update the database when we modify the state of an object inside a
transaction.

41.What is transactional write-behind?
 Hibernate uses a sophisticated algorithm to determine an efficient ordering that
avoids database foreign key constraint violations but is still sufficiently predictable to
the user. This feature is called transactional write-behind.
 42.What are Callback interfaces?
 Callback interfaces allow the application to receive a notification when something
interesting happens to an object—for example, when an object is loaded, saved, or
deleted. Hibernate applications don't need to implement these callbacks, but they're
useful for implementing certain kinds of generic functionality.

Q. How will you configure Hibernate?

Answer:
The configuration files hibernate.cfg.xml (or hibernate.properties) and mapping files
*.hbm.xml are used by the Configuration class to create (i.e. configure and bootstrap
hibernate) the SessionFactory, which in turn creates the Session instances. Session instances
are the primary interface for the persistence service.

" hibernate.cfg.xml (alternatively can use hibernate.properties): These two files are used to
configure the hibernate sevice (connection driver class, connection URL, connection
username, connection password, dialect etc). If both files are present in the classpath then

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hibernate.cfg.xml file overrides the settings found in the hibernate.properties file.

" Mapping files (*.hbm.xml): These files are used to map persistent objects to a relational
database. It is the best practice to store each object in an individual mapping file (i.e
mapping file per class) because storing large number of persistent classes into one mapping
file can be difficult to manage and maintain. The naming convention is to use the same name
as the persistent (POJO) class name. For example Account.class will have a mapping file
named Account.hbm.xml. Alternatively hibernate annotations can be used as part of your
persistent class code instead of the *.hbm.xml files.

Q. What is a SessionFactory? Is it a thread-safe object?

Answer:
SessionFactory is Hibernates concept of a single datastore and is threadsafe so that many
threads can access it concurrently and request for sessions and immutable cache of compiled
mappings for a single database. A SessionFactory is usually only built once at startup.
SessionFactory should be wrapped in some kind of singleton so that it can be easily accessed
in an application code.

SessionFactory sessionFactory = new Configuration().configure().buildSessionfactory();

Q. What is a Session? Can you share a session object between different theads?

Answer:
Session is a light weight and a non-threadsafe object (No, you cannot share it between
threads) that represents a single unit-of-work with the database. Sessions are opened by a
SessionFactory and then are closed when all work is complete. Session is the primary
interface for the persistence service. A session obtains a database connection lazily (i.e. only
when required). To avoid creating too many sessions ThreadLocal class can be used as shown
below to get the current session no matter how many times you make call to the
currentSession() method.

&
public class HibernateUtil {
&
public static final ThreadLocal local = new ThreadLocal();

public static Session currentSession() throws HibernateException {

Session session = (Session) local.get();
//open a new session if this thread has no session
if(session == null) {
session = sessionFactory.openSession();

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local.set(session);
}
return session;
}
}

It is also vital that you close your session after your unit of work completes. Note: Keep your
Hibernate Session API handy.

Q. What are the benefits of detached objects?

Answer:
Detached objects can be passed across layers all the way up to the presentation layer without
having to use any DTOs (Data Transfer Objects). You can later on re-attach the detached
objects to another session.

Q. What are the pros and cons of detached objects?

Answer:
Pros:
" When long transactions are required due to user think-time, it is the best practice to break
the long transaction up into two or more transactions. You can use detached objects from the
first transaction to carry data all the way up to the presentation layer. These detached
objects get modified outside a transaction and later on re-attached to a new transaction via
another session.

Cons
" In general, working with detached objects is quite cumbersome, and better to not clutter up
the session with them if possible. It is better to discard them and re-fetch them on
subsequent requests. This approach is not only more portable but also more efficient because
- the objects hang around in Hibernate's cache anyway.

" Also from pure rich domain driven design perspective it is recommended to use DTOs
(DataTransferObjects) and DOs (DomainObjects) to maintain the separation between Service
and UI tiers.

Q. How does Hibernate distinguish between transient (i.e. newly instantiated) and
detached objects?

Answer " Hibernate uses the version property, if there is one.

" If not uses the identifier value. No identifier value means a new object. This does work only

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for Hibernate managed surrogate keys. Does not work for natural keys and assigned (i.e. not
managed by Hibernate) surrogate keys.
" Write your own strategy with Interceptor.isUnsaved().

 How does hibernate code looks like?

 Show Hibernate overview?
 What are Callback interfaces?
 What are different environments to configure hibernate?
 What are Extension interfaces?
 What are managed associations and hibernate associations?
 What are POJOs?
 What are the benefits of ORM and Hibernate?
 What are the different approaches to represent an inheritance hierarchy?
 What are the different levels of ORM quality?
 What are the different methods of identifying an object?
 What are the Extension interfaces that are there in hibernate?
 What do you create a SessionFactory?
 What does an ORM solution comprises of?
 What does hibernate.properties file consist of?
 What is a hibernate xml mapping document and how does it look like?
 What is a meant by light object mapping?
 What is a meant by medium object mapping?
 What is a pure relational ORM?
 What is Attribute Oriented Programming?
 What is Hibernate?
 What is HQL?
 What is meant by full object mapping?
 What is meant by Method chaining?
 What is object/relational mapping metadata?
 What is ORM?
 What is the file extension you use for hibernate mapping file?
 What should SessionFactory be placed so that it can be easily accessed?
 What the Core interfaces are of hibernate framework?

1. What is Hibernate?
Hibernate is a powerful, high performance object/relational persistence and query service.This
lets the users to develop persistent classes following object-oriented principles such as
association, inheritance, polymorphism, composition, and collections.

2. What is ORM?
ORM stands for Object/Relational mapping. It is the programmed and translucent

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Hibernate
perseverance of objects in a Java application in to the tables of a relational database using the
metadata that describes the mapping between the objects and the database. It works by
transforming the data from one representation to another.

3. What does an ORM solution comprises of?

• It should have an API for performing basic CRUD (Create, Read, Update, Delete)
operations on objects of persistent classes
• Should have a language or an API for specifying queries that refer to the classes
and the properties of classes
• An ability for specifying mapping metadata
• It should have a technique for ORM implementation to interact with transactional
objects to perform dirty checking, lazy association fetching, and other optimization
functions

4. What are the different levels of ORM quality?

There are four levels defined for ORM quality.
i. Pure relational
ii. Light object mapping
iii. Medium object mapping
iv. Full object mapping

5. What is a pure relational ORM?

The entire application, including the user interface, is designed around the relational
model and SQL-based relational operations.

6. What is a meant by light object mapping?

The entities are represented as classes that are mapped manually to the relational tables. The
code is hidden from the business logic using specific design patterns. This approach is successful
for applications with a less number of entities, or applications with common, metadata-driven
data models. This approach is most known to all.

7. What is a meant by medium object mapping?

The application is designed around an object model. The SQL code is generated at build time.
And the associations between objects are supported by the persistence mechanism, and queries
are specified using an object-oriented expression language. This is best suited for medium-sized
applications with some complex transactions. Used when the mapping exceeds 25 different
database products at a time.

8. What is meant by full object mapping?

Full object mapping supports sophisticated object modeling: composition, inheritance,
polymorphism and persistence. The persistence layer implements transparent persistence;
persistent classes do not inherit any special base class or have to implement a special interface.
Efficient fetching strategies and caching strategies are implemented transparently to the
application.
9. What are the benefits of ORM and Hibernate?
There are many benefits from these. Out of which the following are the most important

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Hibernate
one. i. Productivity – Hibernate reduces the burden of developer by providing much of
the functionality and let the developer to concentrate on business logic.
ii. Maintainability – As hibernate provides most of the functionality, the LOC for the
application will be reduced and it is easy to maintain. By automated object/relational
persistence it even reduces the LOC.
iii. Performance – Hand-coded persistence provided greater performance than
automated one. But this is not true all the times. But in hibernate, it provides more
optimization that works all the time there by increasing the performance. If it is
automated persistence then it still increases the performance.
iv. Vendor independence – Irrespective of the different types of databases that are
there, hibernate provides a much easier way to develop a cross platform application.

10. How does hibernate code looks like?

Session session = getSessionFactory().openSession();
Transaction tx = session.beginTransaction();
MyPersistanceClass mpc = new MyPersistanceClass ("Sample App");
session.save(mpc);
tx.commit();
session.close();
The Session and Transaction are the interfaces provided by hibernate. There are many
other interfaces besides this.

11. What is a hibernate xml mapping document and how does it look like?
In order to make most of the things work in hibernate, usually the information is provided in an
xml document. This document is called as xml mapping document. The document defines,
among other things, how properties of the user defined persistence classes’ map to the columns
of the relative tables in database.
<?xml version="1.0"?> <!DOCTYPE hibernate-mapping PUBLIC
"http://hibernate.sourceforge.net/hibernate-mapping-2.0.dtd">
<hibernate-mapping>
<class name="sample.MyPersistanceClass" table="MyPersitaceTable">
<id name="id" column="MyPerId">
<generator class="increment"/>
</id>
<property name="text" column="Persistance_message"/>
<many-to-one name="nxtPer" cascade="all" column="NxtPerId"/>
</class>
</hibernate-mapping>
Everything should be included under <hibernate-mapping> tag. This is the main tag for
an xml mapping document.

12. Show Hibernate overview?

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Hibernate
13. What the Core interfaces are of hibernate framework?
There are many benefits from these. Out of which the following are the most important
one.
i. Session Interface – This is the primary interface used by hibernate applications.
The instances of this interface are lightweight and are inexpensive to create and destroy.
Hibernate sessions are not thread safe.
ii. SessionFactory Interface – This is a factory that delivers the session objects to
hibernate application. Generally there will be a single SessionFactory for the whole
application and it will be shared among all the application threads.
iii. Configuration Interface – This interface is used to configure and bootstrap
hibernate. The instance of this interface is used by the application in order to specify the
location of hibernate specific mapping documents.
iv. Transaction Interface – This is an optional interface but the above three interfaces
are mandatory in each and every application. This interface abstracts the code from any
kind of transaction implementations such as JDBC transaction, JTA transaction.
v. Query and Criteria Interface – This interface allows the user to perform queries
and also control the flow of the query execution.

14. What are Callback interfaces?

These interfaces are used in the application to receive a notification when some object
events occur. Like when an object is loaded, saved or deleted. There is no need to
implement callbacks in hibernate applications, but they’re useful for implementing
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certain kinds of generic functionality.

15. What are Extension interfaces?

When the built-in functionalities provided by hibernate is not sufficient enough, it
provides a way so that user can include other interfaces and implement those interfaces
for user desire functionality. These interfaces are called as Extension interfaces.

16. What are the Extension interfaces that are there in hibernate?
There are many extension interfaces provided by hibernate.
ı ProxyFactory interface - used to create proxies
ı ConnectionProvider interface – used for JDBC connection management
ı TransactionFactory interface – Used for transaction management
ı Transaction interface – Used for transaction management
ı TransactionManagementLookup interface – Used in transaction management.
ı Cahce interface – provides caching techniques and strategies
ı CacheProvider interface – same as Cache interface
ı ClassPersister interface – provides ORM strategies
ı IdentifierGenerator interface – used for primary key generation
ı Dialect abstract class – provides SQL support

17. What are different environments to configure hibernate?

There are mainly two types of environments in which the configuration of hibernate
application differs.
i. Managed environment – In this kind of environment everything from database
connections, transaction boundaries, security levels and all are defined. An example of
this kind of environment is environment provided by application servers such as JBoss,
Weblogic and WebSphere.
ii. Non-managed environment – This kind of environment provides a basic
configuration template. Tomcat is one of the best examples that provide this kind of
environment.

18. What is the file extension you use for hibernate mapping file?
The name of the file should be like this : filename.hbm.xml
The filename varies here. The extension of these files should be “.hbm.xml”.
This is just a convention and it’s not mandatory. But this is the best practice to follow this
extension.

19. What do you create a SessionFactory?

Configuration cfg = new Configuration();
cfg.addResource("myinstance/MyConfig.hbm.xml");
cfg.setProperties( System.getProperties() );
SessionFactory sessions = cfg.buildSessionFactory();
First, we need to create an instance of Configuration and use that instance to refer to the location
of the configuration file. After configuring this instance is used to create the
SessionFactory by calling the method buildSessionFactory().
20. What is meant by Method chaining?

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Hibernate
Method chaining is a programming technique that is supported by many hibernate
interfaces. This is less readable when compared to actual java code. And it is not
mandatory to use this format. Look how a SessionFactory is created when we use method
chaining.
SessionFactory sessions = new Configuration()
.addResource("myinstance/MyConfig.hbm.xml")
.setProperties( System.getProperties() )
.buildSessionFactory();

21. What does hibernate.properties file consist of?

This is a property file that should be placed in application class path. So when the
Configuration object is created, hibernate is first initialized. At this moment the
application will automatically detect and read this hibernate.properties file.
hibernate.connection.datasource = java:/comp/env/jdbc/AuctionDB
hibernate.transaction.factory_class =
net.sf.hibernate.transaction.JTATransactionFactory
hibernate.transaction.manager_lookup_class =
net.sf.hibernate.transaction.JBossTransactionManagerLookup
hibernate.dialect = net.sf.hibernate.dialect.PostgreSQLDialect

22. What should SessionFactory be placed so that it can be easily accessed?

As far as it is compared to J2EE environment, if the SessionFactory is placed in JNDI
then it can be easily accessed and shared between different threads and various
components that are hibernate aware. You can set the SessionFactory to a JNDI by
configuring a property hibernate.session_factory_name in the hibernate.properties file.

23. What are POJOs?

POJO stands for plain old java objects. These are just basic JavaBeans that have defined setter
and getter methods for all the properties that are there in that bean. Besides they can also have
some business logic related to that property. Hibernate applications works efficiently with
POJOs rather then simple java classes.

24. What is object/relational mapping metadata?

ORM tools require a metadata format for the application to specify the mapping between classes
and tables, properties and columns, associations and foreign keys, Java types and SQL types.
This information is called the object/relational mapping metadata. It defines the transformation
between the different data type systems and relationship representations.

25. What is HQL?

HQL stands for Hibernate Query Language. Hibernate allows the user to express queries in its
own portable SQL extension and this is called as HQL. It also allows the user to express in
native SQL.

26. What are the different types of property and class mappings?
• Typical and most common property mapping
<property name="description" column="DESCRIPTION" type="string"/>

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Hibernate
Or
<property name="description" type="string">
<column name="DESCRIPTION"/>
</property>
• Derived properties
<property name="averageBidAmount" formula="( select AVG(b.AMOUNT) from BID b
where b.ITEM_ID = ITEM_ID )" type="big_decimal"/>
• Typical and most common property mapping
<property name="description" column="DESCRIPTION" type="string"/>
• Controlling inserts and updates
<property name="name" column="NAME" type="string"
insert="false" update="false"/>

27. What is Attribute Oriented Programming?

XDoclet has brought the concept of attribute-oriented programming to Java. Until JDK
1.5, the Java language had no support for annotations; now XDoclet uses the Javadoc tag format
(@attribute) to specify class-, field-, or method-level metadata attributes. These attributes are
used to generate hibernate mapping file automatically when the application is built. This kind of
programming that works on attributes is called as Attribute Oriented Programming.

28. What are the different methods of identifying an object?

There are three methods by which an object can be identified.
i. Object identity –Objects are identical if they reside in the same memory location
in the JVM. This can be checked by using the = = operator.
ii. Object equality – Objects are equal if they have the same value, as defined by the
equals( ) method. Classes that don’t explicitly override this method inherit the
implementation defined by java.lang.Object, which compares object identity.
iii. Database identity – Objects stored in a relational database are identical if they
represent the same row or, equivalently, share the same table and primary key value.

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

i. Table per concrete class.
ii. Table per class hierarchy.
iii. Table per subclass.

30. What are managed associations and hibernate associations?

Associations that are related to container management persistence are called managed
associations. These are bi-directional associations. Coming to hibernate associations,
these are unidirectional.

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Hibernate