How to do JPA OneToOne relationship insert only one side of the relation

[Raul De Villa]

Hi folks.

In this moment I'm having a problem with my JPA implementation. I have two Entities as following:

Entity Position

package com.test;

import java.io.Serializable;

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

@Entity(name = "tbl_positions")
public class Position implements Serializable {
        private static final long serialVersionUID = 1L;

        @Id
        @Column(name = "posid")
        private long id;

        @Column(name = "posname")
        private String name;

        public long getId() {
                return id;
        }

        public void setId(long id) {
                this.id = id;
        }

        public String getName() {
                return name;
        }

        public void setName(String name) {
                this.name = name;
        }

}

Entity Employee

package com.test;

import java.io.Serializable;

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


@Entity(name = "tbl_employee")
public class Employee implements Serializable {
        private static final long serialVersionUID = 1L;

        @Id
        @Column(name = "empid")
        private long id;

        @Column(name = "empname")
        private String name;

        @OneToOne(cascade = CascadeType.ALL, fetch = FetchType.EAGER)
        @JoinColumn(name = "emppositionid")
        private Position position;


        public long getId() {
                return id;
        }

        public void setId(long id) {
                this.id = id;
        }

        public String getName() {
                return name;
        }

        public void setName(String name) {
                this.name = name;
        }

       public Position getPosition() {
                return position;
        }

        public void setPosition(Position position) {
                this.position = position;
        }

}

In the other hand I have this Session Bean:

Remote Interface

package com.test;

import javax.ejb.Remote;

@Remote
public interface EmployeeServiceRemote {
        public void createEmployee(Employee employee);
}

Remote Interface Implementation

package com.test;

import javax.ejb.Stateless;
import javax.persistence.EntityManager;
import javax.persistence.PersistenceContext;

@Stateless
public class EmployeeServiceImpl implements EmployeeServiceRemote {

        @PersistenceContext(unitName = "MyPersistenceUnit")
        private EntityManager entityManager;

        public EmployeeServiceImpl() {
        }

        public void createEmployee(Employee employee) {
			Sequence sequence = new Sequence(this.entityManager);
			long nextValue = sequence.getNextValue(SequenceName.EMPLOYEES);
			employee.setId(nextValue);
			this.entityManager.persist(employee);
        }

}

The previous code includes the class Sequence. By the moment it only generates a secuential value for using as primary key for the entity Employee.

This is the content of the file persistence.xml

<?xml version="1.0" encoding="UTF-8"?> <persistence version="2.0" xmlns="http://java.sun.com/xml/ns/persistence" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/persistence http://java.sun.com/xml/ns/persistence/persistence_2_0.xsd"> <persistence-unit name="MyPersistenceUnit"> <jta-data-source>java:/TESTDS</jta-data-source> <class>com.test.PositionEntity</class> <class>com.test.Employee</class> <properties> <property name="hibernate.show_sql" value="true"/> <property name="hibernate.dialect" value="org.hibernate.dialect.MySQLDialect" /> </properties> </persistence-unit> </persistence>

This is my test class:

package com.test;

import javax.naming.Context;

import org.junit.Before;
import org.junit.Test;

public class EmployeeTest {

	private static Employee getNewEmployee() {
		Position position = new Position();
		position.setId(1);
		position.setName("ENGINEER");
		
		Employee employee = new Employee();

		employee.setName("Jhon Doe");
		employee.setPosition(position);
		
		return employee;
	}
	
	private static EmployeeServiceRemote lookUpService() throws Exception {
		EmployeeServiceRemote service = null;
		//Do lookup ...
		return service;
	}
	
	@Test
	public void testCreateEmployee() throws Exception {
		Employee employee = getNewEmployee();
		EmployeeServiceRemote service = lookUpService();
		service.createEmployee(employee);
		System.out.println("Finish !");
	}

}

And finally, this is the database script:
create table tbl_positions ( posid numeric(10) not null, posname varchar(255) not null, primary key(posid) ); create table tbl_employee ( empid numeric(10) not null, empname varchar(255) not null, emppositionid numeric(10) not null, primary key(empid) ); alter table tbl_employee add constraint fk_emp_pos foreign key (emppositionid) references tbl_positions (posid);

Before I executed test class EmployeeTest, I inserted one row in the table tbl_positions like this:
insert into tbl_positions (posid, posname) values (1, 'ENGINEER');

Because tbl_positions is a catalog and it most not be created when I create an Employee.

My problem arise when I executed the test class EmployeeTest. When I invoke the method service.createEmployee(employee), I get the exception: Duplicate entry '1' for key 'PRIMARY' referencing the table tbl_positions. This is a problem for me because what I need is that if a Position already exists, it only creates the Employee. Even better, for business constraints when I create an Employee, all the Positions must exist.

Thanks for any help about it !!

Best tegards,
RADE

[James Boswell]

Your problem is because of the cascade type:

@OneToOne(cascade = CascadeType.ALL, fetch = FetchType.EAGER)  
@JoinColumn(name = "emppositionid")  
private Position position;

So when you attempt to create an Employee with position 1, it cascades this and attempts to create a Position with ID 1 which breaks the primary key constraint as there is already a row with this ID.
Try this instead:

@OneToOne(cascade = CascadeType.REFRESH, fetch = FetchType.EAGER)  
@JoinColumn(name = "emppositionid")  
private Position position;

[Raul De Villa]

Excellent James !!... this solves my problem !

Thank you very much !

[E Armitage]

Why are you assigning some Ids manually?
Better let the persistence provider take care of persistence Ids.