03 - Part-2-Writing-the-Model-Class-with-Annotations

Dialect: It is configuration by which hibernate knows what language needs to use to communication with DB.
Some of the databases have different SQLs to communicate with DB eg: Oracle and postGreSQL. Hibernate uses Dialect to write SQLs and execute queries.

 

* Below Dialect is used for PostgreSQL DB

<!-- SQL dialect -->

      <property name="dialect">

            org.hibernate.dialect.PostgreSQLDialect

      </property>  

 

* If table doesn’t present it will create the table in DB 

     <!-- Drop and re-create the database schema on startup -->

      <property name="hbm2ddl.auto">create</property> 

               

* We need to list out all the MODEL classes

     <!-- Names the annotated entity class -->

      <mapping class="org.yash.dto.UserDetails"/>      

 

@Entity -> It is used for Mapping annotation class

(@Entity declares the class as an entity (i.e. a persistent POJO class))

What is an Entity?

An entity is something that has a distinct, separate existence. An entity could be viewed as a set containing subsets. In philosophy, such sets are said to be abstract objects. In simple language it is Plain Old Java objects without any business logic inside it and mainly used as a Data carry object or value object with may represent the database tuple in form of an object.

Rules for Writing Entity

It is POGO with annotations mapping :-

1. It must have default constructors.
2. It should have getter/setters for all the fields.
3. It should not contain static or final fields.

@Id  -> It is used to define variable name as primary key in database.

(@Id declares the identifier property of this entity.)

 

right click->new file->hibernate.cfg.xml->finish

hibernate.cfg.xml

<?xml version='1.0' encoding='utf-8'?>

<!DOCTYPE hibernate-configuration PUBLIC

        "-//Hibernate/Hibernate Configuration DTD 3.0//EN"

        "http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">

<hibernate-configuration>

    <session-factory>

        <property name="connection.driver_class">

               org.postgresql.Driver

        </property>

        <property name="connection.url">

              jdbc:postgresql://localhost:5433/hibernated

        </property>

        <property name="connection.username">admin</property>

        <property name="connection.password">admin</property>

        <!-- JDBC connection pool (use the built-in) -->

        <property name="connection.pool_size">1</property>

        <!-- SQL dialect -->

        <property name="dialect">

            org.hibernate.dialect.PostgreSQLDialect

        </property>

        <!-- Enable Hibernate's automatic session context management -->

        <property name="current_session_context_class">thread</property>

        <property name="cache.use_query_cache">true</property>

        <property name="cache.use_second_level_cache">true</property>

        <property name="cache.use_structured_entries">true</property>

        <property name="cache.region.factory_class">

             org.hibernate.cache.EhCacheRegionFactory

        </property>

        <property name="net.sf.ehcache.configurationResourceName">

             /hibernate-config/ehcache.xml

        </property>

       

        <!-- Echo all executed SQL to stdout -->

        <property name="show_sql">true</property>

       

        <!-- Drop and re-create the database schema on startup -->

        <property name="hbm2ddl.auto">create</property> 

   

        <!-- Names the annotated entity class -->

        <mapping class="org.yash.dto.UserDetails"/>  

    </session-factory>

</hibernate-configuration>

UserDetails.java

package org.yash.dto;

import javax.persistence.Entity;

import javax.persistence.Id;

@Entity

public class UserDetails {

      @Id

      private int userId;

      private String userName;

      public void setUserId(int userId) {

            this.userId = userId;

      }

      public int getUserId() {

            return userId;

      }

      public void setUserName(String userName) {

            this.userName = userName;

      }

      public String getUserName() {

            return userName;

      }

}