In this example, we will learn about Component Mapping in Hibernate Using Annotations. Component Mapping represents the has-a relationship, the composition is stronger association where the contained object has no existence of its own. For example, Employee has an Address, an address cannot exist separately without Employee. Since the Employee and Address entities are strongly related, it is better to store them in a single table.
Creating table
Create EMPLOYEE Table, simply Copy and Paste the following SQL query in the query editor to get the table created.
CREATE TABLE "EMPLOYEE"
(
"EMP_ID" NUMBER(10,0) NOT NULL ENABLE,
"EMP_NAME" VARCHAR2(255 CHAR),
"DEPARTMENT" VARCHAR2(255 CHAR),
"STREET" VARCHAR2(255 CHAR),
"CITY" VARCHAR2(255 CHAR),
"STATE" VARCHAR2(255 CHAR),
PRIMARY KEY(EMP_ID)
);
Folder Structure:
- Create a simple Maven Project “HibernateTutorial” and create a package for our source files “com.javainterviewpoint” under src/main/java
- Now add the following dependency in the POM.xml
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"> <modelVersion>4.0.0</modelVersion> <groupId>HibernateTutorial</groupId> <artifactId>HibernateTutorial</artifactId> <version>0.0.1-SNAPSHOT</version> <properties> <hibernate.version>4.3.11.Final</hibernate.version> <oracle.connector.version>11.2.0</oracle.connector.version> </properties> <dependencies> <!-- Hibernate --> <dependency> <groupId>org.hibernate</groupId> <artifactId>hibernate-core</artifactId> <version>${hibernate.version}</version> </dependency> <!-- Oracle --> <dependency> <groupId>com.oracle</groupId> <artifactId>ojdbc14</artifactId> <version>${oracle.connector.version}</version> </dependency> </dependencies> <build> <sourceDirectory>src</sourceDirectory> <plugins> <plugin> <artifactId>maven-compiler-plugin</artifactId> <version>3.3</version> <configuration> <source>1.7</source> <target>1.7</target> </configuration> </plugin> </plugins> </build> </project> - Create the Java classes Employee.java, EmployeeAddress.java and ComponentMapping.java under com.javainterviewpoint folder.
- Place the hibernate.cfg.xml under the src/main/resources directory
Component Mapping in Hibernate Using Annotations
EmployeeAddress.java
import javax.persistence.Column;
import javax.persistence.Embeddable;
@Embeddable
public class EmployeeAddress
{
@Column(name="STREET")
private String street;
@Column(name="CITY")
private String city;
@Column(name="STATE")
private String state;
public EmployeeAddress()
{
super();
}
public EmployeeAddress(String street, String city, String state)
{
super();
this.street = street;
this.city = city;
this.state = state;
}
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;
}
@Override
public String toString()
{
return "Employee_Address [street=" + street + ", city=" + city + ", state=" + state + "]";
}
}
We have marked our EmployeeAddress class with @Embeddable annotation so that this class is eligible to be an embeddable class. @Embeddable annotation is used to specify that the EmployeeAddress class will be used as a component. EmployeeAddress cannot have a primary key of its own and it will be using Employee class primary key.
Employee.java
package com.javainterviewpoint;
import javax.persistence.Column;
import javax.persistence.Embedded;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.Table;
@Entity
@Table(name="EMPLOYEE")
public class Employee
{
@Id
@GeneratedValue
@Column(name="EMP_ID")
private int id;
@Column(name="EMP_NAME")
private String name;
@Embedded
private EmployeeAddress address;
public Employee()
{
super();
}
public Employee(int id, String name, EmployeeAddress address)
{
super();
this.id = id;
this.name = name;
this.address = address;
}
public int getId()
{
return id;
}
public void setId(int id)
{
this.id = id;
}
public String getName()
{
return name;
}
public void setName(String name)
{
this.name = name;
}
public EmployeeAddress getAddress()
{
return address;
}
public void setAddress(EmployeeAddress address)
{
this.address = address;
}
@Override
public String toString()
{
return "Employee [id=" + id + ", name=" + name + ", address=" + address + "]";
}
}
We have used the below JPA Annotations in our Employee class
- @Entity – This annotation will mark our Employee class as an Entity Bean.
- @Table – @Table annotation will map our class to the corresponding database table. You can also specify other attributes such as indexes, catalog, schema, uniqueConstraints. The @Table annotation is an optional annotation if this annotation is not provided then the class name will be used as the table name.
- @Id – The @Id annotation marks the particular field as the primary key of the Entity.
- @GeneratedValue – This annotation is used to specify how the primary key should be generated. Here SEQUENCE Strategy will be used as this the default strategy for Oracle
- @Column – This annotation maps the corresponding fields to their respective columns in the database table.
- @Embedded – @Embedded annotation is used to specify that the EmployeeAddress entity should be stored in the EMPLOYEE table as a component.
hibernate.cfg.xml
Place the hibernate.cfg.xml file also under the src/main/resources folder
<?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="hibernate.connection.driver_class">oracle.jdbc.driver.OracleDriver</property> <property name="hibernate.connection.username">root</property> <property name="hibernate.connection.password">root</property> <property name="hibernate.connection.url">jdbc:oracle:thin:@mydb:40051:dev</property> <!-- JDBC connection pool (use the built-in) --> <property name="connection.pool_size">1</property> <!-- SQL dialect --> <property name="hibernate.dialect">org.hibernate.dialect.Oracle10gDialect</property> <!-- Echo all executed SQL to stdout --> <property name="show_sql">true</property> <!-- Drop and re-create the database schema on startup --> <property name="hibernate.hbm2ddl.auto">update</property> <!-- Mapping class --> <mapping class="com.javainterviewpoint.Employee"/> </session-factory> </hibernate-configuration>
- First and foremost property is for specifying the JDBC Driver class, in my case it OracleDriver
<property name="hibernate.connection.driver_class">oracle.jdbc.driver.OracleDriver</property>
- Give the connection URL for connecting the database and provide username and password for connecting the above database
<property name="hibernate.connection.url">jdbc:oracle:thin:@mydb:40051:dev</property> <property name="hibernate.connection.username">root</property> <property name="hibernate.connection.password">root</property>
- Specify the connection pool size, this property limits the number of connections in the Hibernate connection pool.
<property name="connection.pool_size">1</property>
- Dialect Property makes the Hibernate generate the SQL for the corresponding database which is being used. In this example we are using Oracle database hence Oracle query will be generated. If you are using MySQL database then you need to change the dialect accordingly.
<property name="hibernate.dialect">org.hibernate.dialect.Oracle10gDialect</property>
- The show_sql property will print the executed sql in the console when set to true.
<property name="show_sql">true</property>
- If the property “hibernate.hbm2ddl.auto” is set to “create” This will drop and recreate the database schema on every execution. If it is set to “update” then the database schema will be updated every time rather than dropping and recreating.
<property name="hibernate.hbm2ddl.auto">update</property>
- Under the Mapping class tag, we need to specify all the mapping class for which we need the table to be created or updated.
<mapping class="com.javainterviewpoint.Employee"/>
ComponentMapping.java
package com.javainterviewpoint;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.boot.registry.StandardServiceRegistryBuilder;
import org.hibernate.cfg.Configuration;
import org.hibernate.service.ServiceRegistry;
public class ComponentMapping
{
public static void main(String args[])
{
//Reading the hibernate configuration file
Configuration configuration = new Configuration().configure("hibernate.cfg.xml");
StandardServiceRegistryBuilder regBuilber = new StandardServiceRegistryBuilder();
regBuilber.applySettings(configuration.getProperties());
ServiceRegistry serviceRegistry = regBuilber.build();
//Create SessionFacctory
SessionFactory sessionFactory = configuration.buildSessionFactory(serviceRegistry);
//Create Session from SessionFactory
Session session = sessionFactory.openSession();
//Begin the transaction
session.beginTransaction();
//Create a new EmployeeAddress object
EmployeeAddress address = new EmployeeAddress();
address.setStreet("Tharamani");
address.setCity("Chennai");
address.setState("TamilNadu");
//Create a new Employee object
Employee employee = new Employee();
//employee.setId(1);
employee.setName("JavaInterviewPoint");
employee.setAddress(address);
session.save(employee);
//Commit the changes
session.getTransaction().commit();
//Close the session
session.close();
}
}
- Create the Configuration object and read the configuration file using the configure() method.
Configuration configuration = new Configuration().configure("hibernate.cfg.xml");
- Get the SessionFactory object through the buildSessionFactory() method of the configuration object.
SessionFactory sessionFactory = configuration.buildSessionFactory(serviceRegistry);
- openSession() method opens up the new session and begin a new transaction
Session session = sessionFactory.openSession(); session.beginTransaction();
- Create EmployeeAddress and Employee object and set values to its properties
//Create a new EmployeeAddress object
EmployeeAddress address = new EmployeeAddress();
address.setStreet("Tharamani");
address.setCity("Chennai");
address.setState("TamilNadu");
//Create a new Employee object
Employee employee = new Employee();
//employee.setId(1);
employee.setName("JavaInterviewPoint");
employee.setAddress(address);
- save() method of the session object will persist the Employee object
session.save(employee);
- Finally get the transaction and commit the changes and close the session.
session.getTransaction().commit(); session.close();
Console
INFO: HHH000261: Table found: EMPLOYEE Mar 31, 2017 1:25:10 PM org.hibernate.tool.hbm2ddl.TableMetadata <init> INFO: HHH000037: Columns: [emp_name, street, emp_id, state, city] Mar 31, 2017 1:25:10 PM org.hibernate.tool.hbm2ddl.TableMetadata <init> INFO: HHH000108: Foreign keys: [] Mar 31, 2017 1:25:10 PM org.hibernate.tool.hbm2ddl.TableMetadata <init> INFO: HHH000126: Indexes: [sys_c0015424] Mar 31, 2017 1:25:10 PM org.hibernate.tool.hbm2ddl.SchemaUpdate execute INFO: HHH000232: Schema update complete Hibernate: select hibernate_sequence.nextval from dual Hibernate: insert into EMPLOYEE (CITY, STATE, STREET, EMP_NAME, EMP_ID) values (?, ?, ?, ?, ?)
Table
Leave a Reply