Best Hibernate Interview Questions And Answers for 2022 Preparation
Tejasvee Sharma
Feb 13, 2022
Hibernate is the most popular open-source object-relational mapping (ORM) library for Java, which allows developers to write Java code that interacts with relational databases. This article was written to help you improve your knowledge of Hibernate interview questions and answers. This content is meant for people who are looking forward to securing a job in the field of Java, in particular. Hibernate is said to be used by more than 50% of Java developers. We recommend you read the below content that covers all the Hibernate interview questions and answers.
About Hibernate: Hibernate is a Java persistence framework that provides an object-relational mapping (ORM) solution for Java applications. An Object Relational Mapping specifies how to convert persistent in-memory objects into plain old data representation and vice versa. Object-relational mapping is a feature of modern database systems that bridges the gap between objects and tables. The idea is to create a set of objects that represent the conceptual structure of your data and then let the system automatically manage the translation between objects and tables.
Hibernate is an open-source implementation of a lightweight object/relational mapping software engine for Java that uses XML files to store the mapping information. Objects are mapped to tables in a database after which they are persisted by Java and handled using objects.
2. Explain ORM?
ORM (Object Relational Mapping) is the key concept behind the Hibernate framework which creates a bridge between a database and object-oriented programming languages by mapping the database tables with Java classes. It provides a great number of APIs to perform different operations on the data tables.
3. How does Hibernate map the properties of a class to the database columns?
Mapping properties with columns of database tables is possible through XML.
4. What is the use of Configuration Interface in Hibernate?
Hibernate configuration is quite simple; to bootstrap a hibernate application, we need to use its configuration interface. Mapping documents of hibernating areas are found using this interface.
5. What are some ways to improve upon the functionality of built-in interfaces of hibernate?
We can use extensions interfaces in order to add any extra functionality that is not supported by the built-in interfaces.
6. Does all the mapping files of Hibernate have .hbm.xml file extensions to work correctly?
The filename of an HBM file does not need to end in “.hbm.xml”. We can choose any number of extensions for these mapping files.
7. Explain POJOs and their significance?
Plain Old Java Objects (POJOs) are Java objects that have all of the standard getter and setter methods for each property. POJO can be faster and easier to code than Java classes.
8. Explain HQL?
Hibernate is an ORM framework that uses an SQL-like language called HQL (query language) for controlling database access. The HQL language simplifies working with a database and is often compared to plain old SQL.
9. What are the criteria of the API?
Criteria are a simple yet powerful API of Hibernate that provides a mechanism to retrieve entities using the composition of queries.
10. What are the benefits of using Hibernate?
The closing session was automated.
Interaction with hibernate sessions is simplified.
Exception handling is automatic. .
11. What are the two kinds of hibernation?
There are two kinds of hibernation that are:
· Sorted Collection
· Order Collection
12. How do session.save() and session.saveOrUpdate() methods in Hibernate work?
Sessionsave() method inserts a new record only if it’s unique with respect to its primary key and will fail to insert if the primary key is already present. This method can either insert a new record or update an existing record based on the return value of the primary key’s uniqueness.
13. What the benefits are of hibernating over JDBC?
a. Hibernate is one of the most popular object-relational mapping frameworks in the market. Although JDBC allows developers to create databases-specific SQL code, Hibernate requires developers to define what needs updating through XML file so that they don’t have to deal with such programming hassles.
b. Using hibernate, developer doesn’t need to be an expert of writing complex queries as HQL simplifies query writing process. But with JDBC, its the task of developer to write and tune queries.
c. Whenever a pool is not used, it’s destroyed by Java. Hibernate supports that, and so does JDBC.
14. How can we collect hibernate statistics?
We can get hibernate statistics using getStatistics() method of SessionFactory class as shown in the following code:
SessionFactory.getStatistics()
15. What is the transient instance state in Hibernate?
If a context is not active or not persistent for some time, it’s said to be in a transient state.
16. How to reduce DB access time with Hibernate?
Hibernate supports dirty checking, a feature that can reduce the size of your database writes and speed up your queries. Dirty checking looks at every field of an object before it’s changed in the database, to determine if any of them need updating.
17. What is the use of callback interfaces in hibernate?
Hibernating is a function that places an object into a sleep mode that stops it from executing instructions in the processor. The state of an object in the sleep mode is equivalent to that of a hibernated CPU. As such, an event can be triggered when an object resumes normal processing, such as when it’s loaded from the database.
18. Does an instance go to the detached state in hibernation?
If you stop working with an instance that was previously associated with some persistent context (e.g. a table), the instance is said to be in a detached state.
19. What are the four hibernate levels of ORM?
Following are the four ORM levels in hibernate:
a. Medium Object Mapping
b. Pure Relational
c. Full Object Mapping
d. Light Object Mapping
20. How do you set up hibernate on your Mac?
There are two ways to hibernate.
a. XML based configuration ( using hibernate.cfg.xml file)
b. Programmatic configuration ( Using code logic)
21. What is the default cache service of Hibernate?
Hibernate supports multiple cache systems like Ehcache, OSCache, SWARMCache and TreeCache as well as the default cache system is EHCache.
22. Which two are the mapping associations used in hibernation?
There are two types of mappings between entities: Entity-Entity and Entity-Entity To-One.
a. One-to-One Association
b. Many-to-Many Association
23. What is the use of the Hibernate
Hibernate’s QBC (Query By Criteria) API enables the creation of queries by manipulating criteria objects at runtime.
24. How can I re-attach detached objects in Hibernate?
Once a record is removed, it’s impossible to associate that record with an entity in the session, and it can’t be associated again using the merge() method.
25. How does hibernate make its primary key?
The Hibernate mapping XML file (hbm.xml) defines a single, unique column as the primary key of the database table that corresponds to the entity class. It is possible to declare a composite primary key by using multiple columns in the XML file.
26. How many ways can we fetch objects from database with hibernate?
Hibernate has following four ways to get objects from database:
a. Using HQL
b. Using identifier
c. Using Criteria API
d. Using Standard SQL
27. How can we remove hibernation from our system?
Hibernate second level cache can be disabled using one of the following ways :
a. By setting use_second_level_cache as false.
b. By using CACHEMODE.IGNORE
c. Using cache provider as org.hibernate.cache.NoCacheProvider
28. What are ORM metadata?
All of the mapping from the objects to tables, properties to fields, and Java types to SQL types are defined in the ORM metadata.
29. What is the default transaction factory in Hibernate?
When using hibernate 3.2, the default transaction factory is JDBCTransactionFactory.
30. What's the function of JMX in hibernate?
Java applications and components can be monitored using a standard API for Java called the JMX API. This API allows developers to make sure that their applications are running efficiently and robustly over the network
31. How can we bind hibernate session factory to JNDI?
An XML document used by the Hibernate framework is stored in the hibernate.cfg file . The configuration parameters of the file defines how the session factory is bound to JNDI.
32. How many ways are objects identifiable in Hibernate?
Three ways of identifying an object in hibernation are by sight, touch and smell.
a. Using Object Identity: Using == operator.
b. Using Object Equality: Using equals() method.
c. Using database identity: Relational database objects can be identified if they represent the same row.
33. What different fetching methods do they have?
There are many fetching strategies to follow when hibernating:
Join Fetching
Batch Fetching
Select Fetching
Sub-select Fetching
34. How are Java objects mapped to database tables?
We need to use the same column names in a Java bean and database table, to match up the fields that are mapped. If you need a mapping file for your configuration, one is located at the root of the jar file
35. What are the derived properties of a hibernating animal ?
Properties of derived tables may be evaluated and retrieved as necessary. Derived tables should be used only when the SQL statement cannot be written using conventional means.
36. What does the term named SQL query mean in hibernate?
SQL queries are used to communicate with database systems. SQL queries are those queries that are written in the SQL file and are executed wherever they are placed. In hibernate, Named SQL Queries are those queries that are written in a file separate from configuration XML files but referenced there later (HBM mapping can also have this option.).
