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Hibernate Interview Question3

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1.         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 by

pass the setter method and access the instance variable directly while initializing a newly loaded object.

2.         What is the advantage of Hibernate over jdbc?

Hibernate Vs. JDBC :-

 

JDBC

Hibernate
With JDBC, developer has to write code to map an object model’s data representation to a relational data model and its corresponding database schema. 

 

Hibernate is flexible and powerful ORM solution to map Java classes to database tables. Hibernate itself takes care of this mapping using XML files so developer does not need to write code for this. 
With JDBC, the automatic mapping of Java objects with database tables and vice versa conversion is to be taken care of by the developer manually with lines of code. Hibernate provides transparent persistence and developer does not need to write code explicitly to map database tables tuples to application objects during interaction with RDBMS.
JDBC supports only native Structured Query Language (SQL). Developer has to find out the efficient way to access database, i.e. to select effective query from a number of queries to perform same task. Hibernate provides a powerful query language Hibernate Query Language (independent from type of database) that is expressed in a familiar SQL like syntax and includes full support for polymorphic queries. Hibernate also supports native SQL 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 written to map table data to application objects and vice versa is actually to map table fields to object properties. As table changed or database changed then it’s essential to change object structure as well as to change code written to map table-to-object/object-to-table. Hibernate provides this mapping itself. The actual mapping between tables and application objects is done in XML files. If there is change in Database or in any table then the only need to change XML file properties.
                           With JDBC, it is developer’s responsibility to handle JDBC result set and convert it to Java objects through code to use this persistent data in application. So with JDBC, mapping between Java objects and database tables is done manually. 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 performance if client application reads 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 user has updated data. This check has to be added by the developer. Hibernate enables developer to define version type field to application, due to this defined field Hibernate updates version 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

 

3.         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.

4.         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.

5.         What do you mean by fetching strategy ?

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.

6.         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.

7.         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.

8.         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.

9.         What are the types of Hibernate instance states ?

Three types of instance states:

•           Transient -The instance is not associated with any persistence context

•           Persistent -The instance is associated with a persistence context

•           Detached -The instance was associated with a persistence context which has been closed – currently not associated

 

10.       What are the differences between EJB 3.0 & Hibernate?

Hibernate Vs EJB 3.0 :-

Hibernate  EJB 3.0
Session- Cache or collection of loaded objects relating to a single unit of work Persistence Context-Set of entities that can be managed by a given EntityManager is defined by a persistence unit
XDoclet Annotations used to support Attribute Oriented Programming Java 5.0 Annotations used to support Attribute Oriented Programming
Defines HQL for expressing queries to the database Defines EJB QL for expressing queries
Supports Entity Relationships through mapping files and annotations in JavaDoc Support Entity Relationships through Java 5.0 annotations
Provides a Persistence Manager API exposed via the Session, Query, Criteria, and Transaction API Provides and Entity Manager Interface for managing CRUD operations for an Entity

Provides callback support through lifecycle, interceptor, and validatable interfaces

Provides callback support through Entity Listener and Callback methods
Entity Relationships are unidirectional. Bidirectional relationships are implemented by two unidirectional relationships Entity Relationships are bidirectional or unidirectional

 

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