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About Yatin

Yatin
The author is graduated in Electronics & Telecommunication. During his studies, he has been involved with a significant number of projects ranging from programming and software engineering to telecommunications analysis. He works as a technical lead in the information technology sector where he is primarily involved with projects based on Java/J2EE technologies platform and novel UI technologies.

Hibernate Enum Type Mapping Example

In hibernate; developers can map the Java Enum type to a column in the database. In this tutorial, we will explore how a Java Enum type is stored in the database.

1. Introduction

  • Object-Relational Mapping or ORM is the programming technique to map application domain model objects to the relational database tables
  • Hibernate is a Java-based ORM tool that provides the framework for mapping application domain objects to the relational database tables and vice versa. It provides the reference implementation of Java Persistence API that makes it a great choice as an ORM tool with benefits of loose coupling
  • A Framework that an option to map plain old Java objects to the traditional database tables with the use of JPA annotations as well as XML based configuration
Hibernate Enum Type Mapping - Hibernate Overview

Fig. 1: Hibernate Overview

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1.1 Hibernate Annotations

  • Hibernate annotations are the newest way to define mappings without the use of an XML file
  • Developers use annotations to provide metadata configuration along with the Java code. Thus, making the code easy to understand
  • XML provides the ability to change the configuration without building the project. Thus, annotations are less powerful than the XML configuration and should only be used for table and column mappings
  • Annotations are preconfigured with sensible default values, which reduce the amount of coding required. For e.g., Class name defaults to Table name and Field names default to Column names

1.2 Using @Enumerated annotation

An enum type is mapped to a column in the database via the @javax.persistence.Enumerated annotation. This annotation accepts either of the below types to store the enum values i.e.

  • @Enumerated(EnumType.ORDINAL): If the column type is an integer, the ORDINAL parameter is used to insert the values in a numeric format. For e.g. if mobile is the first constant then 0 will be inserted; if landline is the second constant then 1 will be inserted and so on
  • @Enumerated(EnumType.STRING): If the column type is a string, the STRING parameter is used to insert the values in a string format. For e.g. the framework will insert the enum constant name i.e. MOBILE and LANDLINE to the database

Always remember, the default value is EnumType.ORDINAL.

1.3 Download and Install Hibernate

You can read this tutorial in order to download and install Hibernate in the Eclipse IDE.

1.4 Download and Install MySQL

You can watch this video in order to download and install the MySQL database on your Windows operating system.

Now, open up the Eclipse IDE and let us see how to implement this annotation in the hibernate framework!

2. Hibernate Enum Type Mapping Example

Here is a systematic guide for implementing this tutorial in the hibernate framework.

2.1 Tools Used

We are using Eclipse Kepler SR2, JDK 8, MySQL database and Maven. Having said that, we have tested the code against JDK 1.7 and it works well.

2.2 Project Structure

Firstly, let us review the final project structure, in case you are confused about where you should create the corresponding files or folder later!

Hibernate Enum Type Mapping - Application Project Structure

Fig. 2: Application Project Structure

2.3 Project Creation

This section will demonstrate how to create a Java-based Maven project with Eclipse. In Eclipse IDE, go to File -> New -> Maven Project.

Hibernate Enum Type Mapping - Create a Maven Project

Fig. 3: Create a Maven Project

In the New Maven Project window, it will ask you to select the project location. By default, ‘Use default workspace location’ will be selected. Select the ‘Create a simple project (skip archetype selection)’ checkbox and just click on the next button to proceed.

Hibernate Enum Type Mapping - Project Details

Fig. 4: Project Details

It will ask you to ‘Enter the group and the artifact id for the project’. We will input the details as shown in the below image. The version number will be by default: 0.0.1-SNAPSHOT.

Hibernate Enum Type Mapping - Archetype Parameters

Fig. 5: Archetype Parameters

Click on Finish and the creation of a maven project is completed. If you observe, it has downloaded the maven dependencies and a pom.xml file will be created. It will have the following code:

pom.xml

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
	<modelVersion>4.0.0</modelVersion>
	<groupId>com.hibernate</groupId>
	<artifactId>HibernateEnumMapping</artifactId>
	<version>0.0.1-SNAPSHOT</version>
	<name>Hibernate Enum Type Mapping Example</name>
	<packaging>jar</packaging>
</project>

We can start adding the dependencies that developers want like Hibernate, MySQL etc. Let us start building the application!

3. Application Building

Below are the steps involved in developing this application.

3.1 Database and Table Creation

The following script creates a database called enumdb with a table: employee. Open MySQL terminal and execute the script.

CREATE DATABASE IF NOT EXISTS enumdb;

USE enumdb;

CREATE TABLE employee (
	id INT(50) NOT NULL AUTO_INCREMENT, 
	name VARCHAR(200) DEFAULT NULL, 
	designation VARCHAR(200) DEFAULT NULL,
	addr VARCHAR(255) DEFAULT NULL,
	phone INT(10) DEFAULT NULL,
	PRIMARY KEY (id)
);

If everything goes well, the table will be created.

Hibernate Enum Type Mapping - Database and Table Creation

Fig. 6: Database and Table Creation

3.2 Maven Dependencies

Here, we specify the dependencies for the Hibernate framework and the MySQL connector. Maven will automatically resolve the rest dependencies such as Hibernate Core, MySQL etc. The updated file will have the following code:

pom.xml

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
	<modelVersion>4.0.0</modelVersion>
	<groupId>com.hibernate</groupId>
	<artifactId>HibernateEnumMapping</artifactId>
	<version>0.0.1-SNAPSHOT</version>
	<name>Hibernate Enum Type Mapping Example</name>
	<description>A project on enum type mapping in hibernate</description>
	<dependencies>
		<!-- https://mvnrepository.com/artifact/org.hibernate/hibernate-core -->
		<dependency>
			<groupId>org.hibernate</groupId>
			<artifactId>hibernate-core</artifactId>
			<version>5.2.17.Final</version>
		</dependency>
		<!-- https://mvnrepository.com/artifact/mysql/mysql-connector-java -->
		<dependency>
			<groupId>mysql</groupId>
			<artifactId>mysql-connector-java</artifactId>
			<version>8.0.11</version>
		</dependency>
	</dependencies>
	<build>
		<finalName>${project.artifactId}</finalName>
	</build>
</project>

3.3 Java Class Creation

Let us write the Java classes involved in this application.

3.3.1 Implementation of Address enum

Add the following code to the address enum.

Address.java

package com.hibernate.enumModel;

public enum Address {

	PERMANENT, COMMUNICATION
}

3.3.2 Implementation of Phone enum

Add the following code to the phone enum.

Phone.java

package com.hibernate.enumModel;

public enum Phone {

	MOBILE, LANDLINE
}

3.3.3 Implementation of Model

Add the following code to the model definition to map the attributes with the column names.

Employee.java

package com.hibernate.model;

import javax.persistence.Entity;
import javax.persistence.EnumType;
import javax.persistence.Enumerated;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.NamedQuery;
import javax.persistence.Table;

import com.hibernate.enumModel.Address;
import com.hibernate.enumModel.Phone;

@Entity  
@Table(name= "employee")
@NamedQuery(name= "findEmployees", query="from Employee e")
public class Employee {

	@Id
	@GeneratedValue(strategy= GenerationType.IDENTITY)
	private int id;
	private String name;
	private String designation;
	@Enumerated(EnumType.STRING)
	private Address addr;
	@Enumerated(EnumType.ORDINAL)
	private Phone phone;

	public int getId() {
		return id;
	}
	public void setId(int id) {
		this.id = id;
	}
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	public String getDesignation() {
		return designation;
	}
	public void setDesignation(String designation) {
		this.designation = designation;
	}
	public Address getAddr() {
		return addr;
	}
	public void setAddr(Address addr) {
		this.addr = addr;
	}
	public Phone getPhone() {
		return phone;
	}
	public void setPhone(Phone phone) {
		this.phone = phone;
	}

	@Override
	public String toString() {
		return "Employee [id=" + id + ", name=" + name + ", designation=" + designation + ", addr=" + addr + ", phone="
				+ phone + "]";
	}
}

3.3.4 Implementation of Utility class

Add the following code to the implementation class for testing the @Enumerated annotation.

AppMain.java

package com.hibernate.util;

import java.util.List;

import org.hibernate.Session;
import org.hibernate.cfg.Configuration;

import com.hibernate.enumModel.Address;
import com.hibernate.enumModel.Phone;
import com.hibernate.model.Employee;

public class AppMain {

	@SuppressWarnings("unchecked")
	public static void main(String[] args) {		

		// Creating the config instance & passing the hibernate config file.
		Configuration config = new Configuration();
		config.configure("hibernate.cfg.xml");

		// Hibernate session object to start the db transaction.
		Session session = config.buildSessionFactory().openSession();

		session.beginTransaction();

		Employee emp1 = new Employee();
		emp1.setName("Mike");
		emp1.setDesignation("Software Developer");
		emp1.setAddr(Address.COMMUNICATION);
		emp1.setPhone(Phone.MOBILE);

		session.save(emp1);

		Employee emp2 = new Employee();
		emp2.setName("Peter");
		emp2.setDesignation("Manager");
		emp2.setAddr(Address.PERMANENT);
		emp2.setPhone(Phone.LANDLINE);

		session.save(emp2);

		session.getTransaction().commit();

		System.out.println("\n===================\n");

		List list = session.getNamedQuery("findEmployees").getResultList();

		for(Employee myemp : list) {
			System.out.println(myemp.toString());
		}

		// Closing the session object.
		session.close();
	}
}

3.4. Hibernate Configuration File

In the configuration file, we will include the database and the mapping class details.

hibernate.cfg.xml

<?xml version="1.0" encoding="UTF-8"?>
<!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>
		<!-- Database connection settings -->
		<property name="hibernate.connection.driver_class">com.mysql.cj.jdbc.Driver</property>
		<property name="hibernate.connection.url">jdbc:mysql://localhost:3306/enumdb</property>
		<property name="hibernate.connection.username">root</property>
		<property name="hibernate.connection.password" />

		<!-- Validation of the database schema -->
		<property name="hibernate.hbm2ddl.auto">validate</property>

		<!-- Sql dialect -->
		<property name="hibernate.dialect">org.hibernate.dialect.MySQLDialect</property>

		<!-- Printing the sql queries to the console -->
		<property name="show_sql">true</property>

		<!-- Model class -->
		<mapping class="com.hibernate.model.Employee" />
	</session-factory>
</hibernate-configuration>

Important points:

  • Here, we instructed Hibernate to connect to a MySQL database named enumdb and the mapping class to be loaded
  • We have also instructed the Hibernate framework to use MySQLDialect i.e. Hibernate will optimize the generated SQL statements for MySQL
  • This configuration will be used to create a hibernate SessionFactory object
  • show_sql tag will instruct the hibernate framework to log all the SQL statements on the console

4. Run the Application

To run the Hibernate application, Right-click on the AppMain class -> Run As -> Java Application. Developers can debug the example and see what happens after every step!

Hibernate Enum Type Mapping - Run Application

Fig. 7: Run Application

5. Project Demo

The code shows the following logs as the output of this tutorial.

Oct 30, 2018 7:39:56 AM org.hibernate.hql.internal.QueryTranslatorFactoryInitiator initiateService
INFO: HHH000397: Using ASTQueryTranslatorFactory

Hibernate: insert into employee (addr, designation, name, phone) values (?, ?, ?, ?)
Hibernate: insert into employee (addr, designation, name, phone) values (?, ?, ?, ?)

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

Hibernate: select employee0_.id as id1_0_, employee0_.addr as addr2_0_, employee0_.designation as designat3_0_, employee0_.name as name4_0_, employee0_.phone as phone5_0_ from employee employee0_
Employee [id=1, name=Mike, designation=Software Developer, addr=COMMUNICATION, phone=MOBILE]
Employee [id=2, name=Peter, designation=Manager, addr=PERMANENT, phone=LANDLINE]

The result can also be seen using the MySQL console as shown in Fig. 8.

Hibernate Enum Type Mapping - Console output

Fig. 8: Console output

That is all for this tutorial and I hope the article served you whatever you were looking for. Happy Learning and do not forget to share!

6. Conclusion

This post defines the implementation of the @Enumerated annotation in the Hibernate framework and helps developers understand the basic configuration required to achieve this. Developers can download the sample application as an Eclipse project in the Downloads section.

7. Download the Eclipse Project

This was an example of the Hibernate Enum Type Mapping for beginners.

Download
You can download the full source code of this example here: HibernateEnumMapping
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