All about Hibernate Framework

Hibernate

       

     1)      An ORM Tool. Class corresponds to a table and an Object corresponds to a row in the table.

     2)      Used in the data layer of applications

     3)      Implements JPA (Java Persistence API)

     4)      In short, provides a complete solution to implement DAO layer of your Java or JEE application.

Problems:

    1)     Mapping member variables to the column.

    2)     Mapping relationships

    3)     Handling data types.

    4)     Managing changes to object state.

To connect with hibernate, we need to

    1)     Include Hibernate jars and database jdbc jars

What we need to save an Object

    1)     JDBC Database – Hibernate configuration

    2)     Model Object - Annotations

    3)     Service method to create the model object- Hibernate API

    4)     Database design- Not needed

    5)     DAO method to save object using SQL queries- Not needed

Hibernate API

   1)      Create a Session factory – 1 object per application

   2)      Create a Session from the session factory

   3)      Use the Session to save model objects

Annotations used

@Entity(name="USER_DETAILS")

@Id

@GeneratedValue(strategy=GenerationType.AUTO)

IDENTITY-use identity feature of DB

SEQUENCE- Use hibernate sequence object

TABLE-separate table for generating primary key

@Column(name="USER_ID")

@Transient – Ignore field .No column will be created by Hibernate

@Temporal(TemporatlType.DATE) – Ignore timestamp, only store the Date

@Lob – Large objects. Telling hibernate that String field is very large, Examle Description

Natural and Surrogate Key

Serial number column, userId not serving any purpose is surrogate key. Hibernate can do the job for us.(Unique and mandatory )

Email ID address is helping to uniquely distinguish the data is primary key or natural key

Value Object and Entity

Entity has meaning on its own. Thus when it comes to Entity associated with another Entity, new table is created.

Address object doesn’t have meaning by alone, thus it’s a Value Object. No new table is created and address fields are embedded in same table.

@Embeddable – Embed value object to the same Entity. No new table creates.

Proxy Objects in hibernate

      

      1)      Proxy User Class is a dynamic subset of Original User Class.

      2)      When session.get(User.class,1) is called, hibernate returns Proxy User class which pulls only first level fields from DB . This is called lazy initialisation as hibernate isn’t returning Addresses in this case.

      3)    When user.getListOfAddresses() is called, hibernate gives call to Hibernate and fetches all the addresses.