如何使用Hibernate在集合内部持久化实体？

Question

I'm trying to persist an entity in my DB using Hibernate ORM . My entity class

@Entity
@Table(name = "company")
public class Company implements Serializable {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Integer id;

    @Column
    private String name;

    @OneToMany(mappedBy = "company")
    @LazyCollection(LazyCollectionOption.FALSE)
    private Collection<Employee> employees;

Repository

@Repository
@Transactional(propagation = Propagation.REQUIRED)
public class HibernateCompanyRepository implements CompanyRepository {

    @Autowired
    HibernateTemplate template;

    @Override
    public Company getCompany(int id) {
        return template.get(Company.class, id);
    }

    @Override
    public Collection<Company> getCompanies() {
        return template.loadAll(Company.class);
    }

    @Override
    public void addCompany(Company employee) {
        template.save(employee);
    }

    @Override
    public void deleteCompany(int id) {
        template.delete(template.get(Company.class, id));
    }

    @Override
    public void updateCompany(Company company) {
        template.update(company);
    }
}

Here is my controller

@Controller
@RequestMapping("/company")
public class CompanyController {

    @Autowired
    CompanyRepository companyRepository;

    @RequestMapping(value = "/{id}",
                    method = RequestMethod.GET,
                    produces = "application/json")
    @ResponseBody public Company getCompany(@PathVariable("id") Integer id) {
        return companyRepository.getCompany(id);
    }

    @RequestMapping(method = RequestMethod.PUT,
                    consumes = "application/json",
                    headers = "content-type=application/json")
    public String updateCompany(@RequestBody Company company) {
        companyRepository.updateCompany(company);
        return "redirect:/company/" + company.getId();
    }

    // another methods ommited    
}

Old JSON

{
  "name" : "IBM",
  "employees" : [
    {
      "name" : "John",
      "id" : 2
    },
    {
      "name" : "Bill",
      "id" : 4
    }
  ],
  "id" : 2
}

Updated JSON (Bill was deleted)

{
  "name" : "IBM",
  "employees" : [
    {
      "name" : "John",
      "id" : 2
    }
  ],
  "id" : 2
}

I receive an Employee entity in my updateCompany() method. Entity has been succesfully updated. It has changed collection of Employee (for example I removed one employee). But Hibernate can't persist this updated entity. When I'm trying to retrieve it I see no changes happend. Any suggestions how to fix it?

UPD:

I'm trying to update my deleted employees first

@Override
public void updateCompany(Company company) {
    Company oldCompany = getCompany(company.getId());
    for (Employee employee : oldCompany.getEmployees()) {
        if (!company.getEmployees().contains(employee)) {
            employee.setCompany(null);
            template.update(employee);
        }
    }
    template.update(company);
}

And get exception

org.springframework.web.util.NestedServletException: Request processing failed; nested exception is org.springframework.dao.DuplicateKeyException: a different object with the same identifier value was already associated with the session: [eu.flavio.restful.entity.Company#2]; nested exception is org.hibernate.NonUniqueObjectException: a different object with the same identifier value was already associated with the session: [eu.flavio..restful.entity.Company#2]

Answer 1

What matters to Hibernate is the owner side of the bidirectional association. The owner side is the side which does NOT have the mappedBy attribute. That's where it looks to find if an association netween entities exist of not.

The owner side here is thus Employee.company . Company.employees is the inverse side. You must make sure that Bill's company is set to null if you want Bill not to be part of IBM anymore.