Hibernate Development Process :CRUD

To Do List

1. Add Hibernate Configuration file
2. Annotate Java Class
3. Develop Java Code to perform database operations

Hibernate uses JDBC in the background for communicating with the database

So the bulk of the information we will have in our config file is actually JDBC configuration (url, userid, password and so on … ), just to tell hibernate how to connect to the database.

In our Java project within src directory (root of the src directory/ actual class path of our application ) we will create a hibernate.cfg.xml file, which will contain below code:

Step 1: Add hibernate configuration file

=========================(hibernate.cfg.xml)=====================================

<!DOCTYPE hibernate-configuration PUBLIC

        “-//Hibernate/Hibernate Configuration DTD 3.0//EN”

        “http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd“>

<hibernate-configuration>

    <session-factory>

        <!– JDBC Database connection settings –>

        <property name=”connection.driver_class”>com.mysql.cj.jdbc.Driver</property>

        <property name=”connection.url”>jdbc:mysql://localhost:3306/dbname?useSSL=false&amp;serverTimezone=UTC</property>

        <property name=”connection.username”>username</property>

        <property name=”connection.password”>password</property>

        <!– JDBC connection pool settings … using built-in test pool –>

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

        <!– Select our SQL dialect –>

        <property name=”dialect”>org.hibernate.dialect.MySQLDialect</property>

        <!– Echo the SQL to stdout –>

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

<!– Set the current session context –>

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

    </session-factory>

</hibernate-configuration>

=======================================================================

Step 2: Annotate Java Class

Terminology

Entity Class : Java class that is mapped to a database table.

Its plain old java class (POJO) with fields and getters and setters methods and we simply add annotations on it to help with mapping it to a database table

We somehow need to tell Hibernate how to map this class to the actual table and also map fields to the actual columns

Two option for Mapping a class:

1. XML config file (legacy approach)
2. Java Annotations (modern, preferred)
   1. Map class to database table
   2. Map fields to database columns

• @Id is the primary key
• Field name may differ from the database name and in case if we have defined the @Column name then it must be same as the name of a column in the table.
• Also if the field names and the column names are the same there is no need to specify the @Column annotation/attribute as hibernate will automatically pick that up.

Step 3:

Map class to database table

Use below imports as these imports are from java persistence api, it is a standard interface that hibernate implements:

import javax.persistence.Entity;

import javax.persistence.Table;

FAQ: Why we are using JPA Annotation instead of Hibernate ?

QUESTION:

Why we are using JPA Annotation instead of Hibernate ?

For example, why we are not using this org.hibernate.annotations.Entity?

ANSWER:

JPA is a standard specification. Hibernate is an implementation of the JPA specification.

Hibernate implements all of the JPA annotations.

The Hibernate team recommends the use of JPA annotations as a best practice.

Hibernate CRUD Features

Create Object

Data inside MySql table

Note: Generally database generate a primary key (auto incremental ). Now if you wanna be explicit you can tell hibernate how to actually perform generation using given strategy to generate that id.

If we don’t specify anything by default it will use the appropriate strategy for that given database implementation.

@GeneratedValue is a hibernate annotation

Some other type of ID generation Strategies

Most commonly used for MySql is AUTO_INCREMENT which is GenerationType.IDENTITY. That’s a good one because it allows you to leverage the auto increment feature of mysql.

You can also define your own CUSTOM generation strategy.

Create implementation of org.hibernate.id.IdentifierGenerator.

Override the method: public serializable generator( add your custom business logic of incrementing primary key in a sequence ).

Retrieving a Java Object with Hibernate

Query on objects using hibernate

Hibernate Query Language (HQL)

• Query language for retrieving objects
• Similar in nature to SQL
  • Where, like, order by, join, in, etc …

Retrieve all Students

• List<Student> studentList = session.createQuery(“from <table_name>”).getResultList();

Retrieving Students: lastName  = ‘Kavtiyal’

• List<Student> studentList = session.createQuery(“from Student s where s.lastName=’kavtiyal'”).getResultList();

Retrieving Students using OR predicate

• List<Student> studentList = session.createQuery(“from Student s where s.lastName=’kavtiyal’ OR s.firstName=’Adarsh'”).getResultList();

Retrieving Students using LIKE predicate

• List<Student> studentList = session.createQuery(“from Student s where s.email LIKE ‘adarshkavtiyal@gmail.coml’ “).getResultList();

“student”: tableName

“s”: alias

“.lastName”: java object property name

Note: Below Hibernate v5.2 use “session.createQuery(“from Student”).list()” method as in above versions the method has been deprecated.

Update Object

Delete Object

Check out below git repo for a source code of this project:

https://github.com/AdarshKvT/hibernate-demo

Clone:

git clone https://github.com/AdarshKvT/hibernate-demo.git