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

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Q31. What are the disadvantages of Hibernate over native APIs ?

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Q32. Do you like Native SQL Apis like JDBC or JPA / Hibernate ?

Hibernate

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Q33. If you are given choice to avoid LazyInitializationException using any of the following measures, which are the ones you will choose and why ?

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

Hibernate

Ans. First resolution is a big No as it conveys no lazy loading in complete app. even second is advocating the same but for a particular mapping.

third one is most appropriate if loading and dependent entity property access is closer to each other in code and can be accomplished.

I don't mind using 4th too.

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Q34. What does the following exception means

org.hibernate.LazyInitializationException: could not initialize proxy - no Session

Hibernate

Ans. The error states that Hibernate is not able to initialize proxy / dependent entity objects as there is no session or transaction present. Very likely we are trying to load the dependent entities lazily but the call to dependent object property is not wrapped within the session or transaction.

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Q35. If we would like to load just the mapping id for the mapped entity in some cases and whole entity in some cases, because we would like to lazily initialize the dependent entity in some case and not load the entity at all in some case, how can we accomplish that.

For example -

Employee entity is mapped to department entity through department id. We want that when we load employee.getDepartment().getDepartmentId(), it shouldn't load the complete department object but just the Id.

Hibernate

Ans. a

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Q36. If we would like to load just the mapping id for the mapped entity, how can we accomplish that.

For example -

Employee entity is mapped to department entity through department id. We want that when we load employee.getDepartment().getDepartmentId(), it shouldn't load the complete department object but just the Id.

Hibernate

Ans. We can use

@AccessType("property") for getDepartmentId() method within Department class in that case.

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Q37. Can we have 2 entity fields mapped to the same column in Hibernate ?

Hibernate

Ans. No, it's not legal in hibernate. 1 column should be mapped to only one field in entity.

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Q38. What are the methods to connect to database in Java ?

Database

Ans. JDBC ( Java Database Connectivity ),ODBC (Open Database Connectivity), Hibernate, JPA ( Java Persistence API ), JOOQ,MyBatis

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Q39. What is a fetch mode in Hibernate ?

Hibernate

Ans. It specifies an association fetching strategy. It could be DEFAULT, JOIN or SELECT as following

@Fetch(FetchMode.SELECT)

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Q40. Difference between save and flush in Hibernate ?

Hibernate

Ans. Save is used to save the entity to the session whereas flush is to save the session content to DB.

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Q41. How does Lazy Initialization helps improving performance of an application ?

Hibernate

Ans. Lazy Initialization means , Load Dependencies when required. Which means less load on application resources as only required data is loaded upfront. It's not only good for better performance but for better resource utilization too.

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Q42. What are the points to be considered if we move from Eager initialization to Lazy Initialization in Hibernate ?

Hibernate

Ans. Make sure that the properties of dependent Hibernate entities are not accessed and if yes, better wrap the whole code within single transaction.

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Q43. How are DB transactions handled in Hibernate ?

Hibernate

Ans. // Non-managed environment idiom
Session sess = factory.openSession();
Transaction tx = null;
try {
tx = sess.beginTransaction();

// do some work
...

tx.commit();
}
catch (RuntimeException e) {
if (tx != null) tx.rollback();
throw e; // or display error message
}
finally {
sess.close();
}

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Q44. Can we have an entity in hibernate without primary Key ?

Hibernate

Ans. No, Every entity in hibernate needs to have a key, either primary or composite.

If we dont have a primary key on table, there are various ways this problem can be countered.

1. By using composite key on entity ( make sure that the appropriate unique constraint in defined on columns in Database )

2. By mapping Id in entity to ROWID of table.

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Q45. Difference between JDBC and Hibernate ?

Database

Ans. JDBC is a standard Java Api for Database communication whereas Hibernate is an ORM framework that uses JDBC to connect with Database.

Hibernate is another layer of object table mapping over JDBC that provide a database independent, object oriented and an efficient way of database communication.

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Q46. How to specify the or/and combination restrictions within Criteria in Hibernate ?

Hibernate

Ans. session.createCriteria(Employee.class).add( Restrictions.or(Restrictions.like("name", "A%"),Restrictions.like("name", "B%"))).list();

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Frequently asked question in companies using hibernate.

Q47. 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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Q48. 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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Q49. 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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Q50. 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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Q51. 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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Q52. What is Hibernate ?

Hibernate

Ans. Hibernate is a Java ORM Framework.

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Q53. 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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Q54. 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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Q55. 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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Q56. 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 )

Q57. 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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Q58. 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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Q59. 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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Q60. What are the Core Interfaces of Hibernate Framework ?

Hibernate

Ans. Configuration
SessionFactory
Session
Transaction
Query and Citeria

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