Hibernate – Many-to-Many example (Annotation)

In this tutorial, it will reuse the entire infrastructure of the previous “Hibernate many to many example – XML mapping” tutorial, enhance it to support Hibernare / JPA annotation.

Project Structure

Review the new project structure of this tutorial.

1. “Many-to-many” table relationship

See the previous many to many table relationship again.

2. Hibernate Model Class

Update previous model classes –

Stock.java

and

Category.java

, and define new annotation code inside.

File :

Stock.java

package com.mkyong.stock;

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.CascadeType;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.JoinTable;
import javax.persistence.ManyToMany;
import javax.persistence.Table;
import javax.persistence.UniqueConstraint;

@Entity
@Table(name = "stock", catalog = "mkyongdb", uniqueConstraints = {
@UniqueConstraint(columnNames = "STOCK_NAME"),
@UniqueConstraint(columnNames = "STOCK_CODE") })
public class Stock implements java.io.Serializable {

private Integer stockId;
private String stockCode;
private String stockName;
private Set<Category> categories = new HashSet<Category>(0);

public Stock() {
}

public Stock(String stockCode, String stockName) {
this.stockCode = stockCode;
this.stockName = stockName;
}

public Stock(String stockCode, String stockName, Set<Category> categories) {
this.stockCode = stockCode;
this.stockName = stockName;
this.categories = categories;
}

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

public void setStockId(Integer stockId) {
this.stockId = stockId;
}

@Column(name = "STOCK_CODE", unique = true, nullable = false, length = 10)
public String getStockCode() {
return this.stockCode;
}

public void setStockCode(String stockCode) {
this.stockCode = stockCode;
}

@Column(name = "STOCK_NAME", unique = true, nullable = false, length = 20)
public String getStockName() {
return this.stockName;
}

public void setStockName(String stockName) {
this.stockName = stockName;
}

@ManyToMany(fetch = FetchType.LAZY, cascade = CascadeType.ALL)
@JoinTable(name = "stock_category", catalog = "mkyongdb", joinColumns = {
@JoinColumn(name = "STOCK_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;
}

}

File :

Category.java

package com.mkyong.stock;

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.ManyToMany;
import javax.persistence.Table;

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

private Integer categoryId;
private String name;
private String desc;
private Set<Stock> stocks = new HashSet<Stock>(0);

public Category() {
}

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

public Category(String name, String desc, Set<Stock> stocks) {
this.name = name;
this.desc = desc;
this.stocks = stocks;
}

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

public void setCategoryId(Integer categoryId) {
this.categoryId = categoryId;
}

@Column(name = "NAME", nullable = false, length = 10)
public String getName() {
return this.name;
}

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

@Column(name = "DESC", nullable = false)
public String getDesc() {
return this.desc;
}

public void setDesc(String desc) {
this.desc = desc;
}

@ManyToMany(fetch = FetchType.LAZY, mappedBy = "categories")
public Set<Stock> getStocks() {
return this.stocks;
}

public void setStocks(Set<Stock> stocks) {
this.stocks = stocks;
}

}

3. Hibernate Configuration File

Puts annotated classes

Stock.java

and

Category.java

in

hibernate.cfg.xml

like this :

File :

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>
<property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property>
<property name="hibernate.connection.url">jdbc:mysql://localhost:3306/mkyongdb</property>
<property name="hibernate.connection.username">root</property>
<property name="hibernate.connection.password">password</property>
<property name="hibernate.dialect">org.hibernate.dialect.MySQLDialect</property>
<property name="show_sql">true</property>
<mapping class="com.mkyong.stock.Stock" />
<mapping class="com.mkyong.stock.Category" />
</session-factory>
</hibernate-configuration>

4. Run It

Run it, the result is self-explanatory.

File :

App.java

package com.mkyong;

import java.util.HashSet;
import java.util.Set;
import org.hibernate.Session;
import com.mkyong.stock.Category;
import com.mkyong.stock.Stock;
import com.mkyong.util.HibernateUtil;

public class App {
public static void main(String[] args) {

System.out.println("Hibernate many to many (Annotation)");
Session session = HibernateUtil.getSessionFactory().openSession();

session.beginTransaction();

Stock stock = new Stock();
stock.setStockCode("7052");
stock.setStockName("PADINI");

Category category1 = new Category("CONSUMER", "CONSUMER COMPANY");
Category category2 = new Category("INVESTMENT", "INVESTMENT COMPANY");

Set<Category> categories = new HashSet<Category>();
categories.add(category1);
categories.add(category2);

stock.setCategories(categories);

session.save(stock);

session.getTransaction().commit();
System.out.println("Done");
}
}

Output

Hibernate many to many (Annotation)
Hibernate:
insert
into
mkyongdb.stock
(STOCK_CODE, STOCK_NAME)
values
(?, ?)
Hibernate:
insert
into
mkyongdb.category
(`DESC`, NAME)
values
(?, ?)
Hibernate:
insert
into
mkyongdb.category
(`DESC`, NAME)
values
(?, ?)
Hibernate:
insert
into
mkyongdb.stock_category
(STOCK_ID, CATEGORY_ID)
values
(?, ?)
Hibernate:
insert
into
mkyongdb.stock_category
(STOCK_ID, CATEGORY_ID)
values
(?, ?)

Done