Many-To-Many Hibernate Mapping

Many to Many Mapping : A many-to-many relationship refers to a relationship between tables in a database when a parent row in one table contains several child rows in the second table, and vice versa. Many-to-many relationships are often tricky to represent.

Many-to-Many mapping is usually implemented in database using a Join Table, for example we can have Cart, Item table and Cart_Items table for many-to-many mapping. Every cart can have multiple items and every item can be part of multiple carts, so we have a many to many mapping here.
1. Create Database Name is manytomany and Three Table are item, cart_items and cart.
CREATE TABLE `Cart` ( `cart_id` int( 11 ) unsigned NOT NULL AUTO_INCREMENT , `cart_total` decimal( 10, 0 ) NOT NULL , PRIMARY KEY ( `cart_id` ) ) CREATE TABLE `Item` ( `item_id` int( 11 ) unsigned NOT NULL AUTO_INCREMENT , `item_desc` varchar( 20 ) NOT NULL , `item_price` decimal( 10, 0 ) NOT NULL , PRIMARY KEY ( `item_id` ) ) CREATE TABLE `Cart_Items` ( `cart_id` int( 11 ) unsigned NOT NULL , `item_id` int( 11 ) unsigned NOT NULL , PRIMARY KEY ( `cart_id` , `item_id` ) , CONSTRAINT `fk_cart` FOREIGN KEY ( `cart_id` ) REFERENCES `Cart` ( `cart_id` ) , CONSTRAINT `fk_item` FOREIGN KEY ( `item_id` ) REFERENCES `Item` ( `item_id` ) )
Open NetBeans See The Menu Bar go to the file Menu Click on the New Project(Ctrl+Shift+N) and Select Left site categories Java/java web and Project categories to Right Site Project java/web Application .You have to give The Program Name "manytomany". if you wont to save Project Location you can Browse and File save on the direction place and Gone a default Place and Now uncheck/check the check box and click on the next button, select server settings and select the frameworks like Hibernate and go to the finish.
2. hibernate.cfg.xml
<?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.dialect">org.hibernate.dialect.MySQLDialect</property> <property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property> <property name="hibernate.connection.url">jdbc:mysql://localhost:3306/manytomany?zeroDateTimeBehavior=convertToNull</property> <property name="hibernate.connection.username">root</property> <property name="hibernate.show_sql">true</property> <mapping resource="manon/HBM/java/file/Cart.hbm.xml"/> <mapping resource="manon/HBM/java/file/CartItems.hbm.xml"/> <mapping resource="manon/HBM/java/file/Item.hbm.xml"/> </session-factory> </hibernate-configuration>
3. hibernate.reveng.xml
<?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE hibernate-reverse-engineering PUBLIC "-//Hibernate/Hibernate Reverse Engineering DTD 3.0//EN" "http://hibernate.sourceforge.net/hibernate-reverse-engineering-3.0.dtd"> <hibernate-reverse-engineering> <schema-selection match-catalog="manytomany"/> <table-filter match-name="cart"/> <table-filter match-name="cart_items"/> <table-filter match-name="item"/> </hibernate-reverse-engineering>
4. Item.java package manon.HBM.java.file; import java.util.Set; public class Item implements java.io.Serializable { private Integer itemId; private String itemDesc; private long itemPrice; private Set<cart> carts; public Item() { } public Set<cart> getCarts() { return carts; } public void setCarts(Set<cart> carts) { this.carts = carts; } public Item(String itemDesc, long itemPrice) { this.itemDesc = itemDesc; this.itemPrice = itemPrice; } public Integer getItemId() { return this.itemId; } public void setItemId(Integer itemId) { this.itemId = itemId; } public String getItemDesc() { return this.itemDesc; } public void setItemDesc(String itemDesc) { this.itemDesc = itemDesc; } public long getItemPrice() { return this.itemPrice; } public void setItemPrice(long itemPrice) { this.itemPrice = itemPrice; } }
5. CartItems.java
package manon.HBM.java.file; public class CartItems implements java.io.Serializable { private CartItemsId id; public CartItems() { } public CartItems(CartItemsId id) { this.id = id; } public CartItemsId getId() { return this.id; } public void setId(CartItemsId id) { this.id = id; } }
6. CartItemsId.java
package manon.HBM.java.file; public class CartItemsId implements java.io.Serializable { private int cartId; private int itemId; public CartItemsId() { } public CartItemsId(int cartId, int itemId) { this.cartId = cartId; this.itemId = itemId; } public int getCartId() { return this.cartId; } public void setCartId(int cartId) { this.cartId = cartId; } public int getItemId() { return this.itemId; } public void setItemId(int itemId) { this.itemId = itemId; } public boolean equals(Object other) { if ( (this == other ) ) return true; if ( (other == null ) ) return false; if ( !(other instanceof CartItemsId) ) return false; CartItemsId castOther = ( CartItemsId ) other; return (this.getCartId()==castOther.getCartId()) && (this.getItemId()==castOther.getItemId()); } public int hashCode() { int result = 17; result = 37 * result + this.getCartId(); result = 37 * result + this.getItemId(); return result; } }
7. Cart.java
package manon.HBM.java.file; import java.util.Set; public class Cart implements java.io.Serializable { private Integer cartId; private long cartTotal; private Set<item> items; public Cart() { } public Set<item> getItems() { return items; } public void setItems(Set<item> items) { this.items = items; } public Cart(long cartTotal) { this.cartTotal = cartTotal; } public Integer getCartId() { return this.cartId; } public void setCartId(Integer cartId) { this.cartId = cartId; } public long getCartTotal() { return this.cartTotal; } public void setCartTotal(long cartTotal) { this.cartTotal = cartTotal; } }
8. Item.hbm.xml
<?xml version="1.0"?> <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd"> <!-- Generated May 29, 2016 10:33:38 AM by Hibernate Tools 4.3.1 --> <hibernate-mapping> <class name="manon.HBM.java.file.Item" table="item" catalog="manytomany" optimistic-lock="version"> <id name="itemId" type="java.lang.Integer"> <column name="item_id" /> <generator class="identity" /> </id> <property name="itemDesc" type="string"> <column name="item_desc" length="20" not-null="true" /> </property> <property name="itemPrice" type="long"> <column name="item_price" precision="10" scale="0" not-null="true" /> </property> <set name="carts" table="cart_items" fetch="select" cascade="all"> <key column="item_id" /> <many-to-many class="manon.HBM.java.file.Cart" column="cart_id" /> </set> </class> </hibernate-mapping>
9. CartItems.hbm.xml
<?xml version="1.0"?> <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd"> <!-- Generated May 29, 2016 10:33:38 AM by Hibernate Tools 4.3.1 --> <hibernate-mapping> <class name="manon.HBM.java.file.CartItems" table="cart_items" catalog="manytomany" optimistic-lock="version"> <composite-id name="id" class="manon.HBM.java.file.CartItemsId"> <key-property name="cartId" type="int"> <column name="cart_id" /> </key-property> <key-property name="itemId" type="int"> <column name="item_id" /> </key-property> </composite-id> </class> </hibernate-mapping>
10. Cart.hbm.xml
<?xml version="1.0"?> <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd"> <!-- Generated May 29, 2016 10:33:38 AM by Hibernate Tools 4.3.1 --> <hibernate-mapping> <class name="manon.HBM.java.file.Cart" table="cart" catalog="manytomany" optimistic-lock="version"> <id name="cartId" type="java.lang.Integer"> <column name="cart_id" /> <generator class="identity" /> </id> <property name="cartTotal" type="long"> <column name="cart_total" precision="10" scale="0" not-null="true" /> </property> <set name="items" table="cart_items" fetch="select" cascade="all"> <key column="cart_id" /> <many-to-many class="manon.HBM.java.file.Item" column="item_id" /> </set> </class> </hibernate-mapping>
11. ManyToMany.java
package manoj.main.file; import java.util.HashSet; import java.util.Set; import manon.HBM.java.file.Cart; import manon.HBM.java.file.Item; import org.hibernate.Session; import org.hibernate.SessionFactory; import org.hibernate.cfg.Configuration; public class ManyToMany { public static void main(String[] args) { Item iphone = new Item(); iphone.setItemPrice(100); iphone.setItemDesc("iPhone5s"); Item ipod = new Item(); ipod.setItemPrice(50); ipod.setItemDesc("iPod5s"); Set<item> items = new HashSet<item>(); items.add(iphone); items.add(ipod); Cart cart = new Cart(); cart.setItems(items); cart.setCartTotal(50); Cart cart1 = new Cart(); Set<item> items1 = new HashSet<item>(); items1.add(iphone); items1.add(ipod); cart1.setItems(items1); cart1.setCartTotal(100); SessionFactory sessionFactory = null; try{ Configuration cf=new Configuration(); cf.configure("hibernate.cfg.xml"); SessionFactory factory = cf.buildSessionFactory(); Session session1=factory.openSession(); session1.getTransaction().begin(); session1.save(cart); session1.save(cart1); System.out.println("Before committing transaction"); session1.getTransaction().commit(); session1.close(); System.out.println("Cart ID="+cart.getCartId()); System.out.println("Cart1 ID="+cart1.getCartId()); System.out.println("Item1 ID="+iphone.getItemId()); System.out.println("Item2 ID="+ipod.getItemId()); }catch(Exception e){ e.printStackTrace(); } } }
OUTPUT:
Hibernate: insert into manytomany.cart (cart_total) values (?) Hibernate: insert into manytomany.item (item_desc, item_price) values (?, ?) Hibernate: insert into manytomany.item (item_desc, item_price) values (?, ?) Hibernate: insert into manytomany.cart (cart_total) values (?) Before committing transaction Hibernate: insert into cart_items (cart_id, item_id) values (?, ?) Hibernate: insert into cart_items (cart_id, item_id) values (?, ?) Hibernate: insert into cart_items (cart_id, item_id) values (?, ?) Hibernate: insert into cart_items (cart_id, item_id) values (?, ?) Cart ID=7 Cart1 ID=8 Item1 ID=5 Item2 ID=6