In
a one-to-many relationship, each row in the related table can be related to
many rows in the relating table.
For
example an employee object can be mapped to multiple address objects.
package myFirstHibernate; import javax.persistence.Entity; import javax.persistence.GeneratedValue; import javax.persistence.Id; @Entity public class Address { @Id @GeneratedValue private int id; private String street; private String city; private String state; private String PIN; private String country; public int getId() { return id; } public void setId(int id) { this.id = id; } public String getStreet() { return street; } public void setStreet(String street) { this.street = street; } public String getCity() { return city; } public void setCity(String city) { this.city = city; } public String getState() { return state; } public void setState(String state) { this.state = state; } public String getPIN() { return PIN; } public void setPIN(String pIN) { PIN = pIN; } public String getCountry() { return country; } public void setCountry(String country) { this.country = country; } }
package myFirstHibernate; import java.util.ArrayList; import java.util.List; import javax.persistence.CascadeType; import javax.persistence.Entity; import javax.persistence.GeneratedValue; import javax.persistence.Id; import javax.persistence.JoinTable; import javax.persistence.OneToMany; import javax.persistence.JoinColumn; @Entity public class Employee { @Id @GeneratedValue private int id; private String firstName; private String lastName; @OneToMany(cascade=CascadeType.ALL) @JoinTable( name = "emp_address_mapping", joinColumns = @JoinColumn(name = "emp_id"), inverseJoinColumns = @JoinColumn(name = "address_id") ) List<Address> addresses = new ArrayList<Address> (); public int getId() { return id; } public void setId(int id) { this.id = id; } public String getFirstName() { return firstName; } public void setFirstName(String firstName) { this.firstName = firstName; } public String getLastName() { return lastName; } public void setLastName(String lastName) { this.lastName = lastName; } public List<Address> getAddresses() { return addresses; } public void setAddresses(List<Address> addresses) { this.addresses = addresses; } }
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="connection.driver_class">com.mysql.jdbc.Driver</property> <property name="connection.url">jdbc:mysql://localhost/sample</property> <property name="connection.username">root</property> <property name="connection.password">tiger</property> <!-- Enable the logging of all the generated SQL statements to the console --> <property name="show_sql">true</property> <!-- Format the generated SQL statement to make it more readable, --> <property name="format_sql">false</property> <!-- Hibernate will put comments inside all generated SQL statements to hint what’s the generated SQL trying to do --> <property name="use_sql_comments">false</property> <!-- This property makes Hibernate generate the appropriate SQL for the chosen database. --> <property name="dialect">org.hibernate.dialect.MySQLDialect</property> <!-- Drop and re-create the database schema on startup --> <property name="hbm2ddl.auto">create</property> <!-- mappings for annotated classes --> <mapping class="myFirstHibernate.Employee" /> <mapping class="myFirstHibernate.Address" /> </session-factory> </hibernate-configuration>
package myFirstHibernate; import org.hibernate.Session; import org.hibernate.SessionFactory; import org.hibernate.boot.registry.StandardServiceRegistryBuilder; import org.hibernate.cfg.Configuration; public class TestEmployee { /* Step 1: Create session factory */ private static SessionFactory getSessionFactory() { Configuration configuration = new Configuration().configure(); StandardServiceRegistryBuilder builder = new StandardServiceRegistryBuilder(). applySettings(configuration.getProperties()); SessionFactory factory = configuration.buildSessionFactory(builder.build()); return factory; } public static void main(String args[]){ Employee emp1 = new Employee(); emp1.setFirstName("Hari Krishna"); emp1.setLastName("Gurram"); Address addr1 = new Address(); addr1.setCity("Bangalore"); addr1.setCountry("India"); addr1.setPIN("560037"); addr1.setState("Karnataka"); addr1.setStreet("Chowdeswari street"); Address addr2 = new Address(); addr2.setCity("Ongole"); addr2.setCountry("India"); addr2.setPIN("523169"); addr2.setState("Andhra Pradesh"); addr2.setStreet("Punuru"); emp1.getAddresses().add(addr1); emp1.getAddresses().add(addr2); /* To persist data */ SessionFactory sessionFactory = getSessionFactory(); Session session = sessionFactory.openSession(); session.beginTransaction(); session.save(emp1); session.getTransaction().commit(); session.close(); } }
Run
class TestEmployee, you will get output like below.
Hibernate: drop table if exists Address Hibernate: drop table if exists Employee Hibernate: drop table if exists emp_address_mapping Hibernate: create table Address (id integer not null auto_increment, PIN varchar(255), city varchar(255), country varchar(255), state varchar(255), street varchar(255), primary key (id)) Hibernate: create table Employee (id integer not null auto_increment, firstName varchar(255), lastName varchar(255), primary key (id)) Hibernate: create table emp_address_mapping (emp_id integer not null, address_id integer not null) Hibernate: alter table emp_address_mapping add constraint UK_h4s1v5ws5cxqr3eqd5sggdm9v unique (address_id) Hibernate: alter table emp_address_mapping add constraint FK_h4s1v5ws5cxqr3eqd5sggdm9v foreign key (address_id) references Address (id) Hibernate: alter table emp_address_mapping add constraint FK_56nsddme9y6h8uu4kcb127sas foreign key (emp_id) references Employee (id) Dec 21, 2014 2:06:28 PM org.hibernate.tool.hbm2ddl.SchemaExport execute INFO: HHH000230: Schema export complete Hibernate: insert into Employee (firstName, lastName) values (?, ?) Hibernate: insert into Address (PIN, city, country, state, street) values (?, ?, ?, ?, ?) Hibernate: insert into Address (PIN, city, country, state, street) values (?, ?, ?, ?, ?) Hibernate: insert into emp_address_mapping (emp_id, address_id) values (?, ?) Hibernate: insert into emp_address_mapping (emp_id, address_id) values (?, ?)
MySQL
structure looks like below.
mysql> select * from address; +----+--------+-----------+---------+----------------+--------------------+ | id | PIN | city | country | state | street | +----+--------+-----------+---------+----------------+--------------------+ | 1 | 560037 | Bangalore | India | Karnataka | Chowdeswari street | | 2 | 523169 | Ongole | India | Andhra Pradesh | Punuru | +----+--------+-----------+---------+----------------+--------------------+ 2 rows in set (0.00 sec) mysql> select * from employee; +----+--------------+----------+ | id | firstName | lastName | +----+--------------+----------+ | 1 | Hari Krishna | Gurram | +----+--------------+----------+ 1 row in set (0.00 sec) mysql> select * from emp_address_mapping; +--------+------------+ | emp_id | address_id | +--------+------------+ | 1 | 1 | | 1 | 2 | +--------+------------+ 2 rows in set (0.00 sec) mysql> describe employee; +-----------+--------------+------+-----+---------+----------------+ | Field | Type | Null | Key | Default | Extra | +-----------+--------------+------+-----+---------+----------------+ | id | int(11) | NO | PRI | NULL | auto_increment | | firstName | varchar(255) | YES | | NULL | | | lastName | varchar(255) | YES | | NULL | | +-----------+--------------+------+-----+---------+----------------+ 3 rows in set (0.01 sec) mysql> describe address; +---------+--------------+------+-----+---------+----------------+ | Field | Type | Null | Key | Default | Extra | +---------+--------------+------+-----+---------+----------------+ | id | int(11) | NO | PRI | NULL | auto_increment | | PIN | varchar(255) | YES | | NULL | | | city | varchar(255) | YES | | NULL | | | country | varchar(255) | YES | | NULL | | | state | varchar(255) | YES | | NULL | | | street | varchar(255) | YES | | NULL | | +---------+--------------+------+-----+---------+----------------+ 6 rows in set (0.01 sec) mysql> describe emp_address_mapping; +------------+---------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +------------+---------+------+-----+---------+-------+ | emp_id | int(11) | NO | MUL | NULL | | | address_id | int(11) | NO | PRI | NULL | | +------------+---------+------+-----+---------+-------+ 2 rows in set (0.01 sec)
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