handle multiple rows in Spring batch

Question

I ma new to spring batch, I just want to ask how can I retrieve data from multiple rows of result set. I have the following scenario :

1. There are two different table say employee & payroll.
2. An employee can have multiple payroll on the basis of some ID.
3. I have used query select * from emp,pay whem emp.id=pay.id & emp.id = "id".
4. Now it returns multiple row and I have to create an xml

5. The xml structure is :

   <EMP>
   ....
   ...
   <Payroll>
   .
   .
   .
   </Payroll>
   <Payroll>
   .
   .
   .
   </Payroll>
   </emp>
   

While using RowMapper I can only create One payroll child but the table may have multiple childs. Please help...

Answer 1

You need something like a group reader, which is wrapped around your database reader.

I explained this approach in another answer: Spring batch to aggregate values and write single value

Answer 2

This use case is exactly why ORM frameworks like Hibernate were created. Consider using HibernateCursorItemReader for your reader and then defining your persistence layer such that you have the following:

@Entity
@Table(name = "emp")
public class Employee {

    @Id
    @Column(name = "emp_id")
    private Long id;

    @OneToMany(mappedBy="employee")
    private Set<Payment> payments = new HashSet<>();

}

@Entity
@Table(name = "pay")
public class Payment {

    @Id
    @Column(name = "pay_id")
    private Long id;

    @ManyToOne
    @JoinColumn(name = "emp_id")
    private Employee employee;

}