TOP Hibernate Interview Questions and Answers

Read Latest Hibernate Interview Questions and Answers for Freshers, 2+ Years Experienced Q and A with Explanation PDF.

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.

What is ORM?

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

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

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

What is a pure relational ORM?

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

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.

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.

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.

What are the benefits of ORM and Hibernate?

There are many benefits from these. Out of which the following are the most important 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.

How does hibernate code looks like?

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

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
<class name=”sample.MyPersistanceClass” table=”MyPersitaceTable”>
<id name=”id” column=”MyPerId”> <generator class=”increment”/>
<property name=”text” column=”Persistance_message”/>
<many-to-one name=”nxtPer” cascade=”all” column=”NxtPerId”/>
Everything should be included under <hibernate-mapping> tag. This is the main tag for an xml mapping document.

Explain the general flow of Hibernate communication with RDBMS

The general flow of Hibernate communication with RDBMS is :
• The Hibernate configuration is to be loaded and creation of configuration object is done. The mapping of all hbm files will be performed automatically.
• Creation of session factory from the configuration object.
• Obtain a session from the session factory.
• Creation of HQL Query
• Execution of the query in order to get the list of containing java objects.

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.

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 certain kinds of generic functionality.

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.

What are the Extension interfaces that are there in hibernate?

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

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.

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.

What do you create a SessionFactory?

Configuration cfg = new Configuration();
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().

What is meant by Method chaining?

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()
.setProperties( System.getProperties() )


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