Fetch Data using Many To Many Relationship in Hibernate 5

Java Libraries

Copy JAR files which are listed below:

antlr-2.7.7.jar
classmate-1.3.4.jar
commons-lang3-3.6.jar
commons-logging-1.1.3.jar
dom4j-1.6.1.jar
ehcache-core-2.6.11.jar
geolatte-geom-1.1.0.jar
hibernate-commons-annotations-5.0.1.Final.jar
hibernate-core-5.2.11.Final.jar
hibernate-ehcache-5.2.12.Final.jar
hibernate-ejb3-persistence.jar
hibernate-enhance-maven-plugin-4.3.7.Final.jar
hibernate-entitymanager.jar
hibernate-java8-5.2.11.Final.jar
hibernate-jpa-2.1-api-1.0.0.Final.jar
hibernate-spatial-5.2.11.Final.jar
hibernate-validator-6.0.2.Final.jar
javassist-3.16.1-GA.jar
jboss-logging-3.3.1.Final.jar
jboss-transaction-api_1.1_spec-1.0.1.Final.jar
jts-1.11.jar
mysql-connector-java-5.1.36.jar
slf4j-api-1.7.21.jar

Create Database

Create a database with the name is hibernate5. This database have 3 tables: Category table, Product table and Category_Product table. Category table and Product table have a Many to Many. One category can have many products and One product can have many categories.

--
-- Table structure for table `category`
--

CREATE TABLE `category` (
  `id` int(11) NOT NULL PRIMARY KEY AUTO_INCREMENT,
  `name` varchar(250) COLLATE utf8_unicode_ci NOT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci;

--
-- Dumping data for table `category`
--

INSERT INTO `category` (`name`) VALUES('Category 1');
INSERT INTO `category` (`name`) VALUES('Category 2');
INSERT INTO `category` (`name`) VALUES('Category 3');
INSERT INTO `category` (`name`) VALUES('Category 4');

--
-- Table structure for table `product`
--

CREATE TABLE `product` (
  `id` int(11) NOT NULL PRIMARY KEY AUTO_INCREMENT,
  `name` varchar(250) COLLATE utf8_unicode_ci NOT NULL,
  `price` decimal(10,2) NOT NULL,
  `quantity` int(11) NOT NULL,
  `description` text COLLATE utf8_unicode_ci NOT NULL,
  `active` tinyint(1) NOT NULL,
  `creationDate` date NOT NULL,
  `categoryId` int(11) NOT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci;

--
-- Dumping data for table `product`
--

INSERT INTO `product` (`name`, `price`, `quantity`, `description`, `active`, `creationDate`, `categoryId`) VALUES('Laptop 2', '1000.00', 2, 'good', 1, '2016-06-10', 1);
INSERT INTO `product` (`name`, `price`, `quantity`, `description`, `active`, `creationDate`, `categoryId`) VALUES('Laptop 3', '200.00', 5, 'good', 1, '2015-06-15', 1);
INSERT INTO `product` (`name`, `price`, `quantity`, `description`, `active`, `creationDate`, `categoryId`) VALUES('Laptop 4', '500.00', 8, 'good', 0, '2015-06-24', 1);
INSERT INTO `product` (`name`, `price`, `quantity`, `description`, `active`, `creationDate`, `categoryId`) VALUES('Computer 1', '560.00', 10, 'good', 0, '2015-02-25', 2);
INSERT INTO `product` (`name`, `price`, `quantity`, `description`, `active`, `creationDate`, `categoryId`) VALUES('Computer 2', '520.00', 4, 'good', 0, '2015-06-28', 2);
INSERT INTO `product` (`name`, `price`, `quantity`, `description`, `active`, `creationDate`, `categoryId`) VALUES('Computer 3', '720.00', 5, 'good', 1, '2015-08-25', 2);
INSERT INTO `product` (`name`, `price`, `quantity`, `description`, `active`, `creationDate`, `categoryId`) VALUES('Laptop 1', '110.00', 19, 'good', 0, '2016-07-12', 2);
INSERT INTO `product` (`name`, `price`, `quantity`, `description`, `active`, `creationDate`, `categoryId`) VALUES('Mobile 1', '222.00', 5, 'good', 1, '2015-03-16', 3);
INSERT INTO `product` (`name`, `price`, `quantity`, `description`, `active`, `creationDate`, `categoryId`) VALUES('Mobile 2', '1000.00', 4, 'good', 1, '2015-06-27', 3);
INSERT INTO `product` (`name`, `price`, `quantity`, `description`, `active`, `creationDate`, `categoryId`) VALUES('Mobile 3', '1000.00', 4, 'good', 1, '2015-06-27', 3);

--
-- Table structure for table `category_product`
--

CREATE TABLE `category_product` (
  	`category_id` int(11) NOT NULL,
  	`product_id` int(11) NOT NULL,
   	PRIMARY KEY (`category_id`,`product_id`),
	FOREIGN KEY (`category_id`) REFERENCES `category` (`id`),
	FOREIGN KEY (`product_id`) REFERENCES `product` (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci;

--
-- Dumping data for table `category_product`
--

INSERT INTO `category_product` (`category_id`, `product_id`) VALUES(1, 1);
INSERT INTO `category_product` (`category_id`, `product_id`) VALUES(1, 2);
INSERT INTO `category_product` (`category_id`, `product_id`) VALUES(1, 3);
INSERT INTO `category_product` (`category_id`, `product_id`) VALUES(2, 1);
INSERT INTO `category_product` (`category_id`, `product_id`) VALUES(2, 4);
INSERT INTO `category_product` (`category_id`, `product_id`) VALUES(3, 1);
INSERT INTO `category_product` (`category_id`, `product_id`) VALUES(3, 7);

Structure of Category Table

Category Table

Structure of Product Table

Product Table

Structure of Category_Product Table

Category_Product Table

Entities Class

Create two entities classes – Category.java and Product.java, to represent the above tables

Category.java

package entities;

import java.util.HashSet;
import java.util.Set;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.GeneratedValue;
import static javax.persistence.GenerationType.IDENTITY;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.JoinTable;
import javax.persistence.ManyToMany;
import javax.persistence.Table;

@Entity
@Table(name = "category")
public class Category implements java.io.Serializable {

	private Integer id;
	private String name;
	private Set<Product> products = new HashSet<Product>(0);

	public Category() {
	}

	public Category(String name) {
		this.name = name;
	}

	public Category(String name, Set<Product> products) {
		this.name = name;
		this.products = products;
	}

	@Id
	@GeneratedValue(strategy = IDENTITY)
	@Column(name = "id", unique = true, nullable = false)
	public Integer getId() {
		return this.id;
	}

	public void setId(Integer id) {
		this.id = id;
	}

	@Column(name = "name", nullable = false, length = 250)
	public String getName() {
		return this.name;
	}

	public void setName(String name) {
		this.name = name;
	}

	@ManyToMany(fetch = FetchType.LAZY)
	@JoinTable(name = "category_product", catalog = "abc", joinColumns = {
			@JoinColumn(name = "category_id", nullable = false, updatable = false) }, 	inverseJoinColumns = { @JoinColumn(name = "product_id", nullable = false, updatable = false) })
	public Set<Product> getProducts() {
		return this.products;
	}

	public void setProducts(Set<Product> products) {
		this.products = products;
	}

}

Product.java

package entities;

import java.math.BigDecimal;
import java.util.Date;
import java.util.HashSet;
import java.util.Set;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.GeneratedValue;
import static javax.persistence.GenerationType.IDENTITY;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.JoinTable;
import javax.persistence.ManyToMany;
import javax.persistence.Table;
import javax.persistence.Temporal;
import javax.persistence.TemporalType;

@Entity
@Table(name = "product")
public class Product implements java.io.Serializable {

	private Integer id;
	private String name;
	private BigDecimal price;
	private int quantity;
	private String description;
	private boolean active;
	private Date creationDate;
	private Set<Category> categories = new HashSet<Category>(0);

	public Product() {
	}

	public Product(String name, BigDecimal price, int quantity, String description, boolean active, Date creationDate) {
		this.name = name;
		this.price = price;
		this.quantity = quantity;
		this.description = description;
		this.active = active;
		this.creationDate = creationDate;
	}

	public Product(String name, BigDecimal price, int quantity, String description, boolean active, Date creationDate, Set<Category> categories) {
		this.name = name;
		this.price = price;
		this.quantity = quantity;
		this.description = description;
		this.active = active;
		this.creationDate = creationDate;
		this.categories = categories;
	}

	@Id
	@GeneratedValue(strategy = IDENTITY)
	@Column(name = "id", unique = true, nullable = false)
	public Integer getId() {
		return this.id;
	}

	public void setId(Integer id) {
		this.id = id;
	}

	@Column(name = "name", nullable = false, length = 250)
	public String getName() {
		return this.name;
	}

	public void setName(String name) {
		this.name = name;
	}

	@Column(name = "price", nullable = false, precision = 10)
	public BigDecimal getPrice() {
		return this.price;
	}

	public void setPrice(BigDecimal price) {
		this.price = price;
	}

	@Column(name = "quantity", nullable = false)
	public int getQuantity() {
		return this.quantity;
	}

	public void setQuantity(int quantity) {
		this.quantity = quantity;
	}

	@Column(name = "description", nullable = false, length = 65535)
	public String getDescription() {
		return this.description;
	}

	public void setDescription(String description) {
		this.description = description;
	}

	@Column(name = "active", nullable = false)
	public boolean isActive() {
		return this.active;
	}

	public void setActive(boolean active) {
		this.active = active;
	}

	@Temporal(TemporalType.DATE)
	@Column(name = "creationDate", nullable = false, length = 10)
	public Date getCreationDate() {
		return this.creationDate;
	}

	public void setCreationDate(Date creationDate) {
		this.creationDate = creationDate;
	}

	@ManyToMany(fetch = FetchType.LAZY)
	@JoinTable(name = "category_product", catalog = "abc", joinColumns = {
			@JoinColumn(name = "product_id", nullable = false, updatable = false) }, inverseJoinColumns = { @JoinColumn(name = "category_id", nullable = false, updatable = false) })
	public Set<Category> getCategories() {
		return this.categories;
	}

	public void setCategories(Set<Category> categories) {
		this.categories = categories;
	}

}

Hibernate Configuration File

Puts Category.java and Product.java in your Hibernate configuration file, and also MySQL connection details.

<?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="hibernate.enable_lazy_load_no_trans">true</property>
		<property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property>
		<property name="hibernate.connection.password">123456</property>
		<property name="hibernate.connection.url">jdbc:mysql://localhost:3306/hibernate5</property>
		<property name="hibernate.connection.username">root</property>
		<property name="hibernate.dialect">org.hibernate.spatial.dialect.mysql.MySQLSpatialDialect</property>
		<property name="hibernate.current_session_context_class">thread</property>
		<mapping class="entities.Category" />
		<mapping class="entities.Product" />
	</session-factory>
</hibernate-configuration>

Create HibernateUtil class

The HibernateUtil class helps in creating the SessionFactory from the Hibernate configuration file. The SessionFactory is threadsafe, so it is not necessary to obtain one for each thread.

package fetch_data;

import org.hibernate.*;
import org.hibernate.boot.*;
import org.hibernate.boot.registry.*;

public class HibernateUtil {

	private static final SessionFactory sessionFactory;

	static {
		try {
			StandardServiceRegistry standardRegistry = new
					StandardServiceRegistryBuilder()
					.configure("hibernate.cfg.xml")
					.build();
			Metadata metaData = new MetadataSources(
					standardRegistry)
					.getMetadataBuilder()
					.build();
			sessionFactory = metaData.getSessionFactoryBuilder().build();
		} catch (Throwable th) {
			throw new ExceptionInInitializerError(th);
		}
	}

	public static SessionFactory getSessionFactory() {
		return sessionFactory;

	}
}

Create CategoryModel class

The CategoryModel class contains methods to interact with the database.

package fetch_data;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import entities.Category;

public class CategoryModel {

	private SessionFactory sessionFactory = HibernateUtil.getSessionFactory();

	public Category find(int id) {
		Category category = null;
		Session session = null;
		Transaction transaction = null;
		try {
			session = sessionFactory.openSession();
			transaction = session.beginTransaction();
			org.hibernate.query.Query query = session.createQuery("from Category where id = :id");
			query.setParameter("id", id);
			category = (Category) query.uniqueResult();
			transaction.commit();
		} catch (Exception e) {
			category = null;
			if (transaction != null) {
				transaction.rollback();
			}
		} finally {
			session.close();
		}
		return category;
	}

}

Create ProductModel class

The ProductModel class contains methods to interact with the database.

package fetch_data;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import entities.Product;

public class ProductModel {

	private SessionFactory sessionFactory = HibernateUtil.getSessionFactory();

	public Product find(int id) {
		Product product = null;
		Session session = null;
		Transaction transaction = null;
		try {
			session = sessionFactory.openSession();
			transaction = session.beginTransaction();
			org.hibernate.query.Query query = session.createQuery("from Product where id = :id");
			query.setParameter("id", id);
			product = (Product) query.uniqueResult();
			transaction.commit();
		} catch (Exception e) {
			product = null;
			if (transaction != null) {
				transaction.rollback();
			}
		} finally {
			session.close();
		}
		return product;
	}

}

Run It

package fetch_data;

import entities.Category;
import entities.Product;

public class Main {

	public static void main(String[] args) {

		ProductModel productModel = new ProductModel();
		CategoryModel categoryModel = new CategoryModel();

		System.out.println("********* Product Info with id is 1 *********");
		Product product = productModel.find(1);
		System.out.println("Id: " + product.getId());
		System.out.println("Name: " + product.getName());
		System.out.println("Price: " + product.getPrice());
		System.out.println("List of categories of this product");
		for(Category category : product.getCategories()) {
			System.out.println("\tCategory Id: " + category.getId());
			System.out.println("\tCategory Name: " + category.getName());
			System.out.println("\t---------------------------");
		}

		System.out.println("********* Category Info with id is 2 *********");
		Category category = categoryModel.find(2);
		System.out.println("Id: " + category.getId());
		System.out.println("Name: " + category.getName());
		System.out.println("List of products of this category");
		for(Product p : category.getProducts()) {
			System.out.println("\tProduct Id: " + p.getId());
			System.out.println("\tProduct Name: " + p.getName());
			System.out.println("\tPice: " + p.getPrice());
			System.out.println("\t---------------------------");
		}

	}

}

Output

********* Product Info with id is 1 *********
Id: 1
Name: Laptop 2
Price: 1000.00
List of categories of this product
	Category Id: 1
	Category Name: Category 1
	---------------------------
	Category Id: 2
	Category Name: Category 2
	---------------------------
	Category Id: 3
	Category Name: Category 3
	---------------------------

********* Category Info with id is 2 *********
Id: 2
Name: Category 2
List of products of this category
	Product Id: 4
	Product Name: Computer 1
	Pice: 560.00
	---------------------------
	Product Id: 1
	Product Name: Laptop 2
	Pice: 1000.00
	---------------------------