Hibernate Composite Primary Key Tutorial

If a database table has more than one column as the primary key then we call it as composite primary key. In this Hibernate Composite Primary Key tutorial, we will learn how to define Composite Primary Key using <composite-id> tag and Annotations.

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), 
	PRIMARY KEY(EMP_ID,DEPARTMENT)
   );

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 and CompositeKey_Example.java under com.javainterviewpoint folder.
Place the employee.hbm.xml and hibernate.cfg.xml under the src/main/resources directory

Hibernate Composite Primary Key using <composite-id> XML Mapping

Employee.java

package com.javainterviewpoint;

import java.io.Serializable;

public class Employee implements Serializable
{
    private static final long serialVersionUID = 1L;
    
    private int empId;
    private String department;
    private String empName;
   
    public int getEmpId()
    {
        return empId;
    }
    public void setEmpId(int empId)
    {
        this.empId = empId;
    }
    public String getEmpName()
    {
        return empName;
    }
    public void setEmpName(String empName)
    {
        this.empName = empName;
    }
    public String getDepartment()
    {
        return department;
    }
    public void setDepartment(String department)
    {
        this.department = department;
    }
    @Override
    public String toString()
    {
        return "Employee [empId=" + empId + ", department=" + department + ", empName=" + empName + "]";
    }
    @Override
    public int hashCode()
    {
        final int prime = 31;
        int result = 1;
        result = prime * result + ((department == null) ? 0 : department.hashCode());
        result = prime * result + empId;
        return result;
    }
    @Override
    public boolean equals(Object obj)
    {
        if (this == obj)
            return true;
        if (obj == null)
            return false;
        if (getClass() != obj.getClass())
            return false;
        Employee other = (Employee) obj;
        if (department == null)
        {
            if (other.department != null)
                return false;
        } else if (!department.equals(other.department))
            return false;
        if (empId != other.empId)
            return false;
        return true;
    }
}

Our Employee class is a simple POJO class consisting of the getters and setters for the Employee class properties (empId, empName, department). In order to implement Composite Key in Hibernate we need to override the equals() and hashCode() method and also implement the Serializable interface.

employee.hbm.xml

Place the employee.hbm.xml file under the src/main/resources folder

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC
 "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
 "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

<hibernate-mapping package="com.javainterviewpoint">
 <class name="Employee" table="EMPLOYEE">
   <composite-id>
     <key-property name="empId" column="EMP_ID" />
     <key-property name="department" column="DEPARTMENT" />
   </composite-id>
   <property name="empName" column="EMP_NAME" />
 </class>
</hibernate-mapping>

The “employee.hbm.xml” tells hibernate to map “Employee.class” with the “EMPLOYEE” table in the database.
We have a new tag <composite-id> tag added which lets us map composite primary key in hibernate. This tag accepts <key-property> mapping, which holds the individual property which has to be marked as primary key. In our example, empId and department will jointly act as composite primary key.
The property empName is mapped with EMP_NAME column in the table.

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 resource file -->
 <mapping resource="employee.hbm.xml" />
</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 resource tag, we need to specify all the mapping file for which we need the table to be created or updated.

<mapping resource="employee.hbm.xml" />

CompositeKey_Example.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 CompositeKey_Example
{
           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 Employee object
            Employee employee = new Employee();
            //set value to its properties
            employee.setEmpId(1);
            employee.setDepartment("Blogging");
            employee.setEmpName("JavaInterviewPoint");
            
            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 Employee object and set values to its properties

Employee employee = new Employee();
employee.setEmpId(1);
employee.setDepartment("Blogging");
employee.setEmpName("JavaInterviewPoint");

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 01, 2017 5:00:10 PM org.hibernate.tool.hbm2ddl.TableMetadata 
INFO: HHH000037: Columns: [department, emp_name, emp_id]
Mar 01, 2017 5:00:10 PM org.hibernate.tool.hbm2ddl.TableMetadata 
INFO: HHH000108: Foreign keys: []
Mar 01, 2017 5:00:10 PM org.hibernate.tool.hbm2ddl.TableMetadata 
INFO: HHH000126: Indexes: [sys_c0015248]
Mar 01, 2017 5:00:10 PM org.hibernate.tool.hbm2ddl.SchemaUpdate execute
INFO: HHH000232: Schema update complete
Hibernate: insert into Employee (EMP_NAME, EMP_ID, DEPARTMENT) values (?, ?, ?)

Output

Hibernate Composite Primary Key using Annotations

We will be adding JPA Annotation to our Employe class.

package com.javainterviewpoint;

import java.io.Serializable;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.Id;

@Entity
public class Employee implements Serializable
{
    private static final long serialVersionUID = 1L;
    
    @Id
    @GeneratedValue
    @Column(name="EMP_ID")
    private int empId;
    @Id
    @Column(name="DEPARTMENT")
    private String department;
    @Column(name="EMP_NAME")
    private String empName;
   
    public int getEmpId()
    {
        return empId;
    }
    public void setEmpId(int empId)
    {
        this.empId = empId;
    }
    public String getEmpName()
    {
        return empName;
    }
    public void setEmpName(String empName)
    {
        this.empName = empName;
    }
    public String getDepartment()
    {
        return department;
    }
    public void setDepartment(String department)
    {
        this.department = department;
    }
    @Override
    public String toString()
    {
        return "Employee [empId=" + empId + ", department=" + department + ", empName=" + empName + "]";
    }
    @Override
    public int hashCode()
    {
        final int prime = 31;
        int result = 1;
        result = prime * result + ((department == null) ? 0 : department.hashCode());
        result = prime * result + empId;
        return result;
    }
    @Override
    public boolean equals(Object obj)
    {
        if (this == obj)
            return true;
        if (obj == null)
            return false;
        if (getClass() != obj.getClass())
            return false;
        Employee other = (Employee) obj;
        if (department == null)
        {
            if (other.department != null)
                return false;
        } else if (!department.equals(other.department))
            return false;
        if (empId != other.empId)
            return false;
        return true;
    }
}

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. In order to define a composite primary key, we have used @Id annotation twice(empId and department).
@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.

Hibernate Composite Primary Key Tutorial – Using composite-id tag & Annotations