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