JPA : How to convert a native query result set to POJO class collection

Question

I am using JPA in my project.

I came to a query in which I need to make join operation on five tables. So I created a native query which returns five fields.

Answer 1

See example below for using a POJO as pseudo entity to retrieve result from native query without using complex SqlResultSetMapping. Just need two annotations, a bare @Enity and a dummy @Id in your POJO. @Id can be used on any field of your choice, an @Id field can have duplicate keys but not null values.

Since @Enity does not map to any physical table, so this POJO is called a pseudo entity.

Environment: eclipselink 2.5.0-RC1, jpa-2.1.0, mysql-connector-java-5.1.14

You can download complete maven project here

Native query is based on mysql sample employees db http://dev.mysql.com/doc/employee/en/employees-installation.html

persistence.xml

    org.moonwave.jpa.model.pojo.Employee
    
        
        
        
        
    

Employee.java

package org.moonwave.jpa.model.pojo;

@Entity
public class Employee {

@Id
protected Long empNo;

protected String firstName;
protected String lastName;
protected String title;

public Long getEmpNo() {
    return empNo;
}
public void setEmpNo(Long empNo) {
    this.empNo = empNo;
}
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 String getTitle() {
    return title;
}
public void setTitle(String title) {
    this.title = title;
}
public String toString() {
    StringBuilder sb = new StringBuilder();
    sb.append("empNo: ").append(empNo);
    sb.append(", firstName: ").append(firstName);
    sb.append(", lastName: ").append(lastName);
    sb.append(", title: ").append(title);
    return sb.toString();
}
}

EmployeeNativeQuery.java

public class EmployeeNativeQuery {
private EntityManager em;
private EntityManagerFactory emf;

public void setUp() throws Exception {
    emf=Persistence.createEntityManagerFactory("jpa-mysql");
    em=emf.createEntityManager();
}
public void tearDown()throws Exception {
    em.close();
    emf.close();
}

@SuppressWarnings("unchecked")
public void query() {
    Query query = em.createNativeQuery("select e.emp_no as empNo, e.first_name as firstName, e.last_name as lastName," + 
            "t.title from employees e join titles t on e.emp_no = t.emp_no", Employee.class);
    query.setMaxResults(30);
    List list = (List) query.getResultList();
    int i = 0;
    for (Object emp : list) {
        System.out.println(++i + ": " + emp.toString());
    }
}

public static void main( String[] args ) {
    EmployeeNativeQuery test = new EmployeeNativeQuery();
    try {
        test.setUp();
        test.query();
        test.tearDown();
    } catch (Exception e) {
        System.out.println(e);
    }
}
}