hyber

• Hibernate Framework


  Java framework that simplifies the development of Java application to interact with the database

  
• Hibernate


  • Open source
  • Lightweight
  • ORM (Object Relational Mapping) tool
  • Implements the specifications of JPA (Java Persistence API) for data persistence

  
• ORM tool


  • Technique that maps the object stored in the database
  • Simplifies data creation, manipulation, and access
  • Internally uses the Java API to interact with the databases

  
• JPA


  • Defines a set of functionalities, standards, and concepts to the ORM tool
  • Available in the javax.persistence package
  • Allows interaction with the database by decreasing the line of codes for relational object management

  
• Why Hibernate


  • Overcomes the database dependency faced in the JDBC
  • Strengthens the object level relationship - eliminates the impedance mismatch problem
• Hibernate


  • Lightweight framework as it does not contains additional functionalities; it uses only those functionalities required for object-relational mapping
  • Uses persistent classes for data transfer between java application and databases

  
• Hibernate


  • ORM tool which helps in the interaction between the java classes and relational database
  • Solves the problem of data mismatch found in Java application and RDBMS

  
• Hibernate


  • Has its own query language, i.e., HQL (Hibernate Query Language) which is independent of the database
  • HQL is an object-oriented language similar to SQL, but it works with the persistent object and its properties

  
• Hibernate Features


  • Auto-Generation
  • Lazy Loading
  • Database Independent
• Auto-Generation


  Hibernate provides a feature of automatic table generation. It means a programmer need not worry about the query implementation, i.e., Hibernate does on its own.
• Lazy Loading


  • Hibernate supports a new concept called lazy loading. Lazy loading concept retrieves the only necessary object for execution.
  • It also improves the performance of an application.
• Database Independent


  • Hibernate is database-independent as it provides 'Database Dialect' so we need not write SQL queries.
  • It supports many databases such as Oracle, MySql, Sybase, etc.
• Hibernate Architecture


  • Layered architecture with 3 main layers: Application Layer, Hibernate Core Layer, Database Layer

  
• Core Objects of the Hibernate Framework


  • Configuration object
  • SessionFactory object
  • Session object
  • Transaction object
  • Query object
  • Criteria object
• Configuration object


  Consists the configuration file used by the hibernate. It mainly consist the information about database connection (hibernate.cfg.xml) and class mapping (.hbm.xml). Configuration object is used to create the object of SessionFactory.

  
• SessionFactory object


  Created from the Configuration object. It acts as a factory for session objects and client for ConnectionProvider.
• Session object


  Created from the SessionFactory object. It acts as a factory for Transaction, Query and Criteria. Session objects are not thread-safe. It maintains the first level cache.
• Transaction object


  Created from Session object. A transaction object represents an atomic unit of work.
• Query object


  Created from Session object. It uses SQL and HQL to perform database operations.
• Criteria object


  Created from the Session object. It is used to define and execute the object oriented criteria queries.
• First Hibernate Example


  1. Create the Persistent class

  2. Create the mapping file for Persistent class

  3. Create the Configuration file

  4. Create the class that retrieves or stores the persistent object

  5. Build and Run the application

  
• Persistent class


  • A no-arg constructor
  • Provide an identifier property
  • Declare getter and setter methods
• Mapping file name conventionally should be class_name.hbm.xml
• Elements of the mapping file


  • hibernate-mapping
  • class
  • id
  • generator
  • property

  
• Configuration file name conventionally should be hibernate.cfg.xml
• Configuration file contains information about the database and mapping file
• For MySQL database, the configuration file should use org.hibernate.dialect.MySQL5Dialect, com.mysql.jdbc.Driver, jdbc:mysql://localhost:3306, root, root

  
• Entity Association Mapping


  • Mapping of associations between entity classes and the relationships between tables
  • Hibernate provides 4 types of association mapping: One To One, One To Many, Many To One, Many To Many
  • The types of association mapping can be uni-directional or bi-directional