Spring Data JPA save() method not following the hashcode/equals contract

Question

I am facing problems implementing hashcode/equals in a simple Employee Entity below. My custom field upon which i want to implement equality is the "_id" field.

When i save two employee objects with the same value i.e. "111", I expect to save only one value in the database. However, i end up saving 2 employee records.

The entity code is as below

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

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    @Column(name = "employee_id")
    private Long employeeId;

    @Column(name = "employeehexa_id") 
    private String _id;

    @Override
    public int hashCode() {
        HashCodeBuilder hcb = new HashCodeBuilder();
        hcb.append(_id);
        return hcb.toHashCode();
    }   


    @Override
    public boolean equals(Object obj) {
        if (this == obj) {
            return true;
        }
        if (!(obj instanceof Employee)) {
            return false;
        }
        Employee that = (Employee) obj;
        EqualsBuilder eb = new EqualsBuilder();
        eb.append(_id, that._id);
        return eb.isEquals();
    }

    // Required Constructors, getters, setters not shown for brevity
   }

And the below is my call to save two object with same _id

@Autowired
private EmployeeRepo employeeRepo;

@RequestMapping("/test")
String Test() throws Exception {

    Employee e1 = new Employee("111");
    Employee e2 = new Employee("111");
     System.out.println(e1.equals(e2)); // prints true, implying hashcode and equals working fine
    employeeRepo.save(e1);
    employeeRepo.save(e2);//Both e1 and e2 are saved inspite of being equal

    return "Completed !";
}

The equality check seems to work fine. Is there something about save() of spring JpaRepository that causes this or is my understanding of how equality/hashcode contract is enforced incorrect ?

I thought i understood equality/hashcode but looks like that is not the case. Any help appreciated. Thx.

This has nothing to do with Spring Data JPA but merely with how JPA works. If you don't want to save it create a unique constraint on the database level. — M. Deinum, Feb 05 '18 at 10:09

score 2 · Accepted Answer · edited Feb 05 '18 at 09:48

2

According to this answer, https://stackoverflow.com/a/11881628/5695673, you probably have 2 records because your fields employeeId are differents for your entities, so for spring-data the two entities are differents.
To test if your equals()/hashCode() works as expected, you can try to put your entities in a collection which check object equality (i.e. a Set) and try to save all the set in one time.

Example:

Set<Employee> employees = new HashSet<Employee>();
employees.add( new Employee("111"));
employees.add( new Employee("111"));

System.out.println(employees.size()); //1
employeeRepo.save(employees); // 1 record

More information here: https://developer.jboss.org/wiki/EqualsandHashCode?_sscc=t

edited Feb 05 '18 at 09:48

STaefi

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answered Feb 05 '18 at 09:29

gWombat

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thanks. Yes, I am aware of the collection approach. But was interested in saving separately. Is the only way to ensure that spring data save() enforces the hashcode/equals is to put objects in a collection and save them ? – HopeKing Feb 05 '18 at 10:10
IMO yes, but this is not a spring-data problem, this is more a JPA related topic. – gWombat Feb 05 '18 at 11:09

Spring Data JPA save() method not following the hashcode/equals contract

1 Answers1