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Spring Data JPA Many To Many Foreign Key Example

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Previously we have learnt how to do One To One and One To Many Mapping using Spring Data JPA, in this article, we will learn about Spring Data JPA Many to Many mapping. Let’s take the Example of Employee and Address, one Employee can have many Address and similarly, one Address can have many Employees. Let’s dig into the code.

In Many-to-Many relationship a mediator table is mandatory, this table stores the primary key of both tables (EMPLOYEE and ADDRESS) as a foreign key.

Creating table

Create EMPLOYEE and ADDRESS Tables, 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, 
 "NAME" VARCHAR2(255 CHAR), 
 
 PRIMARY KEY ("EMP_ID")
 );
 
 CREATE TABLE "ADDRESS" 
 ( 
 "ADDR_ID" NUMBER(10,0) NOT NULL ENABLE, 
 "STREET" VARCHAR2(255 CHAR), 
 "CITY" VARCHAR2(255 CHAR), 
 "STATE" VARCHAR2(255 CHAR), 
 "COUNTRY" VARCHAR2(255 CHAR), 

 PRIMARY KEY ("ADDR_ID")
 );
 
 CREATE TABLE "EMPLOYEE_ADDRESS" 
 ( 
 "EMP_ID" NUMBER(10,0) NOT NULL ENABLE, 
 "ADDR_ID" NUMBER(10,0) NOT NULL ENABLE, 
 
 PRIMARY KEY (EMP_ID , ADDR_ID),
 CONSTRAINT FK_EMP_ID FOREIGN KEY (EMP_ID) REFERENCES EMPLOYEE (EMP_ID),
 CONSTRAINT FK_ADDR_ID FOREIGN KEY (ADDR_ID) REFERENCES ADDRESS (ADDR_ID)
 );

Folder Structure:

Spring Data JPA Many To Many

  1. Create a simple Maven Project “SpringDataJPA” and create a package for our source files “com.javainterviewpoint” under  src/main/java 
  2. 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/maven-v4_0_0.xsd">
 <groupId>com.javainterviewpoint</groupId>
 <artifactId>SpringJPA</artifactId>
 <packaging>jar</packaging>
 <version>0.0.1-SNAPSHOT</version>
 <name>SpringJPA Maven Webapp</name>
 <url>http://maven.apache.org</url>
 <properties>
    <hibernate.version>4.2.0.Final</hibernate.version>
    <spring.version>4.3.5 RELEASE</spring.version>
 </properties>

 <dependencies>
    <!-- DB related dependencies -->

     <dependency>
        <groupId>org.hibernate.common</groupId>
        <artifactId>hibernate-commons-annotations</artifactId>
        <version>4.0.5.Final</version>
    </dependency>
    <dependency>
       <groupId>org.hibernate</groupId>
       <artifactId>hibernate-entitymanager</artifactId>
       <version>4.1.9.Final</version>
    </dependency>
    <dependency>
       <groupId>commons-dbcp</groupId>
       <artifactId>commons-dbcp</artifactId>
       <version>1.4</version>
    </dependency>
    <dependency>
       <groupId>javassist</groupId>
       <artifactId>javassist</artifactId>
       <version>3.12.1.GA</version>
    </dependency>
    <dependency>
       <groupId>org.hibernate.javax.persistence</groupId>
       <artifactId>hibernate-jpa-2.0-api</artifactId>
       <version>1.0.1.Final</version>
    </dependency>
    <dependency>
       <groupId>org.springframework.data</groupId>
       <artifactId>spring-data-jpa</artifactId>
       <version>1.11.3.RELEASE</version>
    </dependency>
    <dependency>
       <groupId>com.oracle</groupId>
       <artifactId>ojdbc14</artifactId>
       <version>11.2.0</version>
    </dependency>
    <dependency>
       <groupId>org.hibernate</groupId>
       <artifactId>hibernate-core</artifactId>
       <version>4.1.9.Final</version>
    </dependency>

    <!-- SPRING -->
    <dependency>
       <groupId>org.springframework</groupId>
       <artifactId>spring-tx</artifactId>
       <version>4.3.5.RELEASE</version>
    </dependency>
    <dependency>
       <groupId>org.springframework</groupId>
       <artifactId>spring-context</artifactId>
       <version>4.3.5.RELEASE</version>
    </dependency>
    <dependency>
       <groupId>org.springframework</groupId>
       <artifactId>spring-webmvc</artifactId>
       <version>4.3.5.RELEASE</version>
    </dependency>
    <dependency>
       <groupId>org.springframework</groupId>
       <artifactId>spring-core</artifactId>
       <version>4.3.5.RELEASE</version>
    </dependency>
    <dependency>
       <groupId>org.springframework</groupId>
       <artifactId>spring-tx</artifactId>
       <version>4.3.5.RELEASE</version>
    </dependency>
    <dependency>
       <groupId>org.springframework</groupId>
       <artifactId>spring-jdbc</artifactId>
       <version>4.3.5.RELEASE</version>
    </dependency>
    <dependency>
       <groupId>org.springframework</groupId>
       <artifactId>spring-orm</artifactId>
       <version>3.2.5.RELEASE</version>
    </dependency>

    <!-- CGLIB is required to process @Configuration classes -->
    <dependency>
       <groupId>cglib</groupId>
       <artifactId>cglib</artifactId>
       <version>2.2.2</version>
    </dependency>

    <!-- Servlet API and JSTL -->
    <dependency>
       <groupId>javax.servlet</groupId>
       <artifactId>javax.servlet-api</artifactId>
       <version>3.0.1</version>
       <scope>provided</scope>
    </dependency>
    <dependency>
       <groupId>jstl</groupId>
       <artifactId>jstl</artifactId>
       <version>1.2</version>
    </dependency>

    <!-- Test -->
    <dependency>
       <groupId>junit</groupId>
       <artifactId>junit</artifactId>
       <version>4.7</version>
       <scope>test</scope>
    </dependency>
    <dependency>
       <groupId>org.springframework</groupId>
       <artifactId>spring-test</artifactId>
       <version>4.3.5.RELEASE</version>
       <scope>test</scope>
    </dependency>
    <dependency>
       <groupId>org.springframework</groupId>
       <artifactId>spring-test-mvc</artifactId>
       <version>1.0.0.M1</version>
       <scope>test</scope>
    </dependency>
   </dependencies>
  <build>
     <finalName>SpringJPA</finalName>
 </build>
</project>
  3. Create the Java classes Employee.java, Address.java, EmployeeRepository.java, SaveLogic.java and RetrieveLogic.java under  com.javainterviewpoint folder.
  4. Place the SpringConfig.xml under the src/main/resources  directory

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Spring Data JPA Many To Many Foreign Key Example

Employee.java

Create a new Java file Employee.java under the package com.javainterviewpoint and add the following code

package com.javainterviewpoint;

import java.util.Set;

import javax.persistence.CascadeType;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.JoinTable;
import javax.persistence.ManyToMany;
import javax.persistence.Table;

@Entity
@Table(name="EMPLOYEE")
public class Employee
{
    @Id
    @GeneratedValue
    @Column(name="EMP_ID")
    private int empId;
    
    @Column(name="NAME")
    private String empName;

    @ManyToMany(cascade = CascadeType.ALL,fetch=FetchType.EAGER)
    @JoinTable(name="EMPLOYEE_ADDRESS", 
                joinColumns={@JoinColumn(name="EMP_ID")}, 
                inverseJoinColumns={@JoinColumn(name="ADDR_ID")})
    private Set<Address> address;
 
    public Employee()
    {
        super();
    }

    public Employee(int empId, String empName, Set<Address> address)
    {
        super();
        this.empId = empId;
        this.empName = empName;
        this.address = address;
    }

    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 Set<Address> getAddress()
    {
        return address;
    }

    public void setAddress(Set<Address> address)
    {
        this.address = address;
    }

    @Override
    public String toString()
    {
        return "Employee [empId=" + empId + ", empName=" + empName + ", address=" + address + "]";
    }
}

Our Employee class is a simple POJO class consisting of the getters and setters for the Employee properties (empId, empName, address).

In the POJO class, we have used the below JPA Annotations.

  1. @Entity – This annotation will mark our Employee class as an Entity Bean.
  2. @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.
  3. @Id –  The @Id annotation marks the particular field as the primary key of the Entity.
  4. @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
  5. @ManyToMany – This annotation specifies that there exists a many to many relationship between Employee and Address.
  6. @JoinTable – This annotation is used to define the Linking Table(Employee_Address). It should be defined by the relationship owner here our Employee Class is the relationship owner.
  7. @JoinColumn – This annotation defines the joining column in both the tables.
  8. @Column – This annotation maps the corresponding fields to their respective columns in the database table.

Address.java

Create a new Java file Address.java under the package com.javainterviewpoint and add the following code

package com.javainterviewpoint;

import java.io.Serializable;
import java.util.Set;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.ManyToMany;
import javax.persistence.Table;


@Entity
@Table(name="ADDRESS")
public class Address
{
    @Id
    @Column(name = "ADDR_ID")
    @GeneratedValue
    private int addrId;
    
    @Column(name="STREET")
    private String street;
    @Column(name="CITY")
    private String city;
    @Column(name="STATE")
    private String state;
    @Column(name="COUNTRY")
    private String country;
    
    @ManyToMany(mappedBy="address")
    private Set<Employee> employee;

    public Address()
    {
        super();
    }

    public Address(int addrId, String street, String city, String state, String country, Set<Employee> employee)
    {
        super();
        this.addrId = addrId;
        this.street = street;
        this.city = city;
        this.state = state;
        this.country = country;
        this.employee = employee;
    }

    public int getAddrId()
    {
        return addrId;
    }

    public void setAddrId(int addrId)
    {
        this.addrId = addrId;
    }

    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 getCountry()
    {
        return country;
    }

    public void setCountry(String country)
    {
        this.country = country;
    }

    public Set<Employee> getEmployee()
    {
        return employee;
    }

    public void setEmployee(Set<Employee> employee)
    {
        this.employee = employee;
    }

    @Override
    public String toString()
    {
        return "Address [addrId=" + addrId + ", street=" + street + ", city=" + city + ", state=" + state + ", country="
                + country + ", employee=" + employee + "]";
    }
}

SpringConfig.xml

Place the SpringConfig.xml file also under the src/main/resources folder

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:jdbc="http://www.springframework.org/schema/jdbc"
	xmlns:context="http://www.springframework.org/schema/context" xmlns:tx="http://www.springframework.org/schema/tx"
	xmlns:jpa="http://www.springframework.org/schema/data/jpa"
	xsi:schemaLocation="http://www.springframework.org/schema/jdbc		http://www.springframework.org/schema/jdbc/spring-jdbc-3.1.xsd
		http://www.springframework.org/schema/beans		http://www.springframework.org/schema/beans/spring-beans.xsd
		http://www.springframework.org/schema/tx/		http://www.springframework.org/schema/tx/spring-tx-3.2.xsd
		http://www.springframework.org/schema/context		http://www.springframework.org/schema/context/spring-context.xsd
		http://www.springframework.org/schema/mvc		http://www.springframework.org/schema/mvc/spring-mvc.xsd
		http://www.springframework.org/schema/data/jpa		http://www.springframework.org/schema/data/jpa/spring-jpa-1.2.xsd">


 <context:component-scan base-package="com.javainterviewpoint"></context:component-scan>
 <jpa:repositories base-package="com.javainterviewpoint"
 entity-manager-factory-ref="entityManagerFactoryBean"></jpa:repositories>
 
 <bean id="saveLogic" class="com.javainterviewpoint.SaveLogic" />
 <bean id="retrieveLogic" class="com.javainterviewpoint.RetrieveLogic" />

 <!--EntityManagerFactory -->
 <bean id="entityManagerFactoryBean"
 class="org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean">
   <property name="dataSource" ref="dataSource" />
   <!-- Now /META-INF/persistence.xml is no longer needed -->
   <property name="packagesToScan" value="com.javainterviewpoint" />
   <property name="jpaVendorAdapter">
      <bean class="org.springframework.orm.jpa.vendor.HibernateJpaVendorAdapter" />
   </property>
   <property name="jpaProperties">
     <props>
       <prop key="hibernate.hbm2ddl.auto">update</prop>
       <prop key="hibernate.dialect">org.hibernate.dialect.Oracle10gDialect</prop>
     </props>
   </property>
 </bean>

 <bean id="dataSource"
 class="org.springframework.jdbc.datasource.DriverManagerDataSource">
   <property name="driverClassName" value="oracle.jdbc.driver.OracleDriver" />
   <property name="url" value="jdbc:oracle:thin:@rsh2:40051:mydb" />
   <property name="username" value="root" />
   <property name="password" value="root" />
 </bean>

 <bean id="transactionManager" class="org.springframework.orm.jpa.JpaTransactionManager">
    <property name="entityManagerFactory" ref="entityManagerFactoryBean" />
 </bean>
</beans>

We have defined the below beans in our SpringConfig file.

  • dataSource : This bean holds all the database related configurations such as driverClassName, url, username, password.
  • entityManagerFactoryBean: This is the important bean where in which we will be passing the datasource reference and set values to the properties jpaVendorAdapter, jpaProperties
  • transactionManager: We are using the JpaTransactionManager for managing the transactions for our application, we will be passing the entityManagerFactoryBean reference to it.

EmployeeRepository.java

Our EmployeeRepository interface extends the JpaRepository interface. The JpaRepository interface contains the basic methods for performing CRUD Operations over an entity. Learn more about the list of methods here.

package com.javainterviewpoint;

import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.stereotype.Component;

public interface EmployeeRepository extends JpaRepository<Employee,Integer>
{

}

SaveLogic.java

package com.javainterviewpoint;

import java.util.ArrayList;
import java.util.HashSet;
import java.util.List;
import java.util.Set;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.support.ClassPathXmlApplicationContext;
import org.springframework.stereotype.Component;

@Component
public class SaveLogic
{
    private static SaveLogic saveLogic;

    @Autowired
    private EmployeeRepository employeeRepository;

    public static void main(String[] args)
    {
        // Reading the Configuration file
        ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext("springConfig.xml");

        // Get the SaveLogic bean
        saveLogic = (SaveLogic) context.getBean("saveLogic");

        saveLogic.saveEmployee();

        context.close();
    }

    public void saveEmployee()
    {
        //Create a new Employee object employee1
        Employee employee1 = new Employee();
        employee1.setEmpName("JIP1");
        
        //Create a new Employee object employee2
        Employee employee2 = new Employee();
        employee2.setEmpName("JIP2");
        
        //Create a new Address object address1
        Address address1 = new Address();
        address1.setStreet("Street 1");
        address1.setCity("City 1");
        address1.setCountry("Country 1");
        address1.setState("State 1");

        //Create a new Address object address2
        Address address2 = new Address();
        address2.setStreet("Street 2");
        address2.setCity("City 2");
        address2.setCountry("Country 2");
        address2.setState("State 2");

        //Adding address1 and address2 to addressSet
        Set<Address> addressSet = new HashSet<Address>();
        addressSet.add(address1);
        addressSet.add(address2);
       
        employee1.setAddress(addressSet);
        employee2.setAddress(addressSet);
        
        //Add both employee object to a list
        List<Employee> empList= new ArrayList<Employee>();
        empList.add(employee1);
        empList.add(employee2);
        
        //Saving the empList
        employeeRepository.save(empList);
        
        System.out.println("Employee and Employee Address saved successfully!!");
    }
}
  • In our SaveLogic class, we have read the Configuration file(SpringConfig.xml) and get all the bean definition through ClassPathXmlApplicationContext
ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext("springConfig.xml");
  • Get the SaveLogic Class instance by calling the getBean() method over the context created.
saveLogic = (SaveLogic)context.getBean("saveLogic");
  • Call the saveEmployee() method
saveLogic.saveEmployee();
  • Set the values for the Properties of two Employee instances (employee1 & employee2)and Address (address1 & address2)class
  • Instead of calling the save() method twice for saving two employee instances we have created a list of employee and pass it to the save() method [save() method is already implemented by JpaRepository ]

Console:

INFO: HHH000261: Table found: ADDRESS
Jun 30, 2017 3:52:31 PM org.hibernate.tool.hbm2ddl.TableMetadata <init>
INFO: HHH000037: Columns: [street, state, addr_id, country, city]
Jun 30, 2017 3:52:31 PM org.hibernate.tool.hbm2ddl.TableMetadata <init>
INFO: HHH000108: Foreign keys: []
Jun 30, 2017 3:52:31 PM org.hibernate.tool.hbm2ddl.TableMetadata <init>
INFO: HHH000126: Indexes: [sys_c0016002]
Jun 30, 2017 3:52:34 PM org.hibernate.tool.hbm2ddl.TableMetadata <init>
INFO: HHH000261: Table found: EMPLOYEE
Jun 30, 2017 3:52:34 PM org.hibernate.tool.hbm2ddl.TableMetadata <init>
INFO: HHH000037: Columns: [name, emp_id]
Jun 30, 2017 3:52:34 PM org.hibernate.tool.hbm2ddl.TableMetadata <init>
INFO: HHH000108: Foreign keys: []
Jun 30, 2017 3:52:34 PM org.hibernate.tool.hbm2ddl.TableMetadata <init>
INFO: HHH000126: Indexes: [sys_c0016004]
Jun 30, 2017 3:52:36 PM org.hibernate.tool.hbm2ddl.TableMetadata <init>
INFO: HHH000261: Table found: EMPLOYEE_ADDRESS
Jun 30, 2017 3:52:36 PM org.hibernate.tool.hbm2ddl.TableMetadata <init>
INFO: HHH000037: Columns: [emp_id, addr_id]
Jun 30, 2017 3:52:36 PM org.hibernate.tool.hbm2ddl.TableMetadata <init>
INFO: HHH000108: Foreign keys: [fk_emp_id, fk_addr_id]
Jun 30, 2017 3:52:36 PM org.hibernate.tool.hbm2ddl.TableMetadata <init>
INFO: HHH000126: Indexes: [sys_c0016007]
Jun 30, 2017 3:52:36 PM org.hibernate.tool.hbm2ddl.SchemaUpdate execute
INFO: HHH000232: Schema update complete
Employee and Employee Address saved successfully!!

RetrieveLogic.java

package com.javainterviewpoint;

import java.util.List;
import java.util.Set;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.support.ClassPathXmlApplicationContext;
import org.springframework.stereotype.Component;

@Component
public class RetrieveLogic
{
    private static RetrieveLogic retrieveLogic;

    @Autowired
    private EmployeeRepository employeeRepository;

    public static void main(String[] args)
    {
        // Reading the Configuration file
        ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext("springConfig.xml");

        // Get the RetrieveLogic bean
        retrieveLogic = (RetrieveLogic) context.getBean("retrieveLogic");

        retrieveLogic.retrieveEmployee();

        context.close();
    }
    public void retrieveEmployee()
    {
        // Get list of all Employee & Address
        List<Employee> employeeList = employeeRepository.findAll();

        // Displaying the Employee details
        for (Employee employee : employeeList)
        {
            System.out.println("*** Employee Details ***");

            System.out.println("Employee Id   : " + employee.getEmpId());
            System.out.println("Employee Name : " + employee.getEmpName());

            System.out.println("*** Employee Address Details ***");
            Set<Address> empAddressSet = employee.getAddress();
            for (Address employeeAddress : empAddressSet)
            {
                System.out.println("Street  : " + employeeAddress.getStreet());
                System.out.println("City    : " + employeeAddress.getCity());
                System.out.println("State   : " + employeeAddress.getState());
                System.out.println("Country : " + employeeAddress.getCountry());
            }
        }
    }
}
  • In our RetrieveLogic class, we have read the Configuration file(SpringConfig.xml) and get all the bean definition through ClassPathXmlApplicationContext
ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext("springConfig.xml");
  • Get the SaveLogic Class instance by calling the getBean() method over the context created.
retrieveLogic= (retrieveLogic)context.getBean("saveLogic");
  • Call the retrieveEmployee() method
retrieveLogic.retrieveEmployee ();
  • Call the findAll() method over the employeeRepository instance [findAll() method is already implemented by JpaRepository ]

Output:

*** Employee Details ***
Employee Id : 137
Employee Name : JIP1
*** Employee Address Details ***
Street : Street 1
City : City 1
State : State 1
Country : Country 1
Street : Street 2
City : City 2
State : State 2
Country : Country 2
*** Employee Details ***
Employee Id : 140
Employee Name : JIP2
*** Employee Address Details ***
Street : Street 1
City : City 1
State : State 1
Country : Country 1
Street : Street 2
City : City 2
State : State 2
Country : Country 2

   Download Source Code

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