Hibernate - Interview Questions and Answers for 'Hibernate' | Search Interview Question

Hibernate - Interview Questions and Answers for 'Hibernate' - 92 question(s) found - Order By Newest

Frequently asked question in companies using Hibernate.

Q1. What is Lazy Initialization in Hibernate ?

Ans. It's a feature to lazily initialize dependencies , relationship and associations from the Database. Any related references marked as @OneToMany or @ManyToMany are loaded lazily i.e when they are accessed and not when the parent is loaded.

Sample Code for Lazy Initialization

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Q2. What are the ways to avoid LazyInitializationException ?

Hibernate

Ans. 1. Set lazy=false in the hibernate config file.

2. Set @Basic(fetch=FetchType.EAGER) at the mapping.

3. Make sure that we are accessing the dependent objects before closing the session.

4. Force initialization using Hibernate.initialize

5. Using Fetch Join in HQL.

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Frequently asked question in companies using hibernate.

Q3. Difference between first level and second level cache in hibernate ?

Hibernate

Ans. 1. First level cache is enabled by default whereas Second level cache needs to be enabled explicitly.

2. First level Cache came with Hibernate 1.0 whereas Second level cache came with Hibernate 3.0.

3. First level Cache is Session specific whereas Second level cache is shared by sessions that is why First level cache is considered local and second level cache is considered global.

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Q4. Which annotations are used in Hibernate ?

Hibernate

Ans. @Entity
@Table
@Id
@Column
@Temporal
@Basic
@Enumerated
@Access
@Embeddable
@Lob
@AttributeOverride
@Embedded
@GeneratedValue
@ElementCollection
@JoinTable
@JoinColumn
@CollectionId
@GenericGenerator
@OneToOne
@OneToMany
@ManyToOne
@ManyToMany
@NotFound

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Q5. What are the contents of Hibernate configuration file ( hibernate.cfg.xml ) ?

Hibernate

Ans. HBM Files ( Mapping )
DB Connection ( DB Connection String , User Name , Password , Pool Size )
SQL Dialect ( SQL variant to be generated )
Show SQL ( Show / No show SQL on Console )
Auto Commit ( True / False )

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Q6. What things you would care about to improve the performance of Application if its identified that its DB communication that needs to be improved ?

Solution

Ans. 1. Query Optimization ( Query Rewriting , Prepared Statements )

2. Restructuring Indexes.

3. DB Caching Tuning ( if using ORM )

4. Identifying the problems ( if any ) with the ORM Strategy ( If using ORM )

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Q7. How to configure second level cache in Hibernate ?

Hibernate

Ans. 1. Configure Provider class in Hibernate configuration file.

2. Add Cache usage tag ( read-only or read-write ) in mapping files ( hbm ).

3. Create an XML file called ehcache.xml and place in classpath which contains time settings and update settings, behavior of cache , lifetime and idletime of Pojos, how many objects are allowed.

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Q8. What is the use of @GeneratedValue annotation in Hibernate?

Hibernate

Ans. This annotation is added to the auto increment column with the strategy to increment the column value. Usually this is added to the surrogate primary key column and specified with the Database Sequence.

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Q9. What are the disadvantages of Hibernate over native APIs ?

Hibernate

^{This question is still unanswered. Can you please provide an answer.}

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Q10. What are the advantages of Hibernate ?

Hibernate

Ans. 1. No need to know SQL, RDBMS, and DB Schema.
2. Underlying Database can be changed without much effort by changing SQL dialect and DB connection.
3.Improved Performance by means of Caching.

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Q11. What is the purpose of dialect configured in Hibernate configuration file ?

Hibernate

Ans. It tells the framework which SQL varient to generate.

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Q12. Please specify in what sequence the objects of following classes will be created ?

Session , SessionFactory, Query , Configuration

Hibernate

Ans. Configuration -> SessionFactory -> Session -> Query

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Very frequently asked Hibernate interview question. Frequently asked in TCS ( based on 2 feedback )

Q13. What are different types of associations in Hibernate ?

Hibernate

Ans. There are 4 types of associations in Hibernate

One to One
One to Many
Many to One
Many to Many

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Q14. What are the configuration files in Hibernate ?

Hibernate

Ans. hibernate.cfg.xml ( Main Configuration File )

and *.hbm.xml files ( Mapping Files )

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Q15. What are the Core Interfaces of Hibernate Framework ?

Hibernate

Ans. Configuration
SessionFactory
Session
Transaction
Query and Citeria

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Q16. What are collection types in Hibernate ?

Hibernate

Ans. Bag, Set , List , Array, Map

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Very frequently asked if being interviewed for hibernate. Frequently asked in Tata Consultancy (TCS) and Overstock.com

Q17. Difference between load and get ?

Hibernate

Ans. If id doesnt exist in the DB load throws an exception whereas get returns null in that case.get makes the call to DB immediately whereas load makes the call to proxy.

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Q18. What is the way to rollback transaction if something goes wrong using hibernate API ?

Hibernate

Ans. We can have the code calling Hibernate API within try block and can have transaction.rollback within Catch.

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Q19. What are the restrictions for the entity classes ?

Hibernate

Ans. 1. Entity classes should have default constructor.

2. Entity classes should be declared non final.

3. All elements to be persisted should be declared private and should have public getters and setters in the Java Bean style.

4. All classes should have an ID that maps to Primary Key for the table.

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Q20. What are some differences between Spring caching and Hibernate caching?

Hibernate

Ans. Spring caching makes use of its intercepting capabilities to add caching to method calls. Therefore, the entire object is cached and reused. Hibernate, on the other hand, has more domain-specific knowledge of the Entity being cached and can handle the objects more appropriately.

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Q21. Do you like Native SQL Apis like JDBC or JPA / Hibernate ?

Hibernate

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Q22. What are the the methods to clear cache in Hibernate ?

Hibernate

Ans. Evict() and clear(). Evist is used to clear a particular object from the cache whereas clear clears the complete local cache.

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Q23. What are different types of second level cache ?

Hibernate

Ans. 1. EHCache ( Easy Hibernate )
2. OSCache ( Open Symphony )
3. Swarm Cache ( JBoss )
4. Tree Cache ( JBoss )

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Q24. Can we disable first level cache ? What should one do if we don't want an object to be cached ?

Hibernate

Ans. No.We can either call evict after the object retrieval or can use separate sessions.

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Q25. What is Hibernate ?

Hibernate

Ans. Hibernate is a Java ORM Framework.

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Q26. What are the different types of inheritance in Hibernate ?

Hibernate

Ans. Table Per Class , Table per Sub Class , Table per Concrete Class

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Q27. What is lazy fetching in Hibernate ?

Hibernate

Ans. Lazy fetching is the technique of not loading the child objects when parent objects are loaded. By default Hibernate does not load child objects. One can specify whether to load them or not while doing the association.

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Q28. Different types of Hibernate Instance States ?

Hibernate

Ans. Transient - In this state, an instance is not associated with any persistence context
Persistent - In this state, an instance is associated with a persistence context
Detached - This is a state for an instance which was previously associated with a persistence context an has been currently closed dissociated

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Q29. Which class elements are not persisted ?

Hibernate

Ans. Static and Transient.

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Q30. What entries we make in the hibernate config file if we are not using hbm files but Annotations ?

Hibernate

Ans. We configure Entity classes having annotated mappings.

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