支持读取和删除但不支持插入的一对多关系

Question

我想将前面文章中提到的要求扩展到支持删除。我们有两个数据模型对象组织和部门共享一对多的关系。通过下面的映射，我可以从organization对象读取部门列表。我没有添加cascade ALL属性来限制在创建组织时添加部门。

@Entity
@Table(name="ORGANIZATIONS")
public class Organization{

    @Id
    @GeneratedValue
    Private long id;

    @Column(unique=true)
    Private String name;

    @OneToMany(mappedBy = "organization", fetch = FetchType.EAGER)
    private List<Department> departments;


}

@Entity
@Table(name="DEPARTMENTS")
Public class Department{

   @Id
   @GeneratedValue
   Private long id;

   @Column(unique=true)
   Private String name;


   @ManyToOne(fetch = FetchType.EAGER)
   private Organization organization;

}

organizationRepository.deleteById(orgId);

@RunWith(SpringJUnit4ClassRunner.class)
@DataJpaTest
@Transactional
public class OrganizationRepositoryTests {

    @Autowired
    private OrganizationRepository organizationRepository;

    @Autowired
    private DepartmentRepository departmentRepository;



    @Test
    public void testDeleteOrganization() {
        final organization organization = organizationRepository.findByName(organizationName).get(); //precondition

        Department d1 = new Department();
        d1.setName("d1");

        d1.setorganization(organization);

        Department d2 = new Department();
        d2.setName("d2");

        d2.setorganization(organization);

        departmentRepository.save(d1);
        departmentRepository.save(d2);

//        assertEquals(2, organizationRepository.getOne(organization.getId()).getDepartments().size()); //this assert is failing. For some reason organizations does not have a list of departments

        organizationRepository.deleteById(organization.getId());

        assertFalse(organizationRepository.findByName(organizationName).isPresent());
        assertEquals(0, departmentRepository.findAll().size()); //no departments should be found

    }

}

Answer 1

有关失败原因,请参阅代码注释：

@RunWith(SpringJUnit4ClassRunner.class)
@DataJpaTest
@Transactional
public class OrganizationRepositoryTests {

    @Autowired
    private OrganizationRepository organizationRepository;

    @Autowired
    private DepartmentRepository departmentRepository;

    @PersistenceContext
    private Entitymanager em;

    @Test
    public void testDeleteOrganization() {
        Organization organization = 
                organizationRepository.findByName(organizationName).get(); 

        Department d1 = new Department();
        d1.setName("d1");
        d1.setOrganization(organization);

        Department d2 = new Department();
        d2.setName("d2");
        d2.setOrganization(organization);

        departmentRepository.save(d1);
        departmentRepository.save(d2);

        // this fails because there is no trip to the database as Organization 
        // (the one loaded in the first line)
        // already exists in the current entityManager - and you have not 
        // updated its list of departments.
        // uncommenting the following line will trigger a reload and prove 
        // this to be the case: however it is not a fix for the issue.

        // em.clear();

         assertEquals(2,
             organizationRepository.getOne(
               organization.getId()).getDepartments().size()); 

        //similary this will execute without error with the em.clear() 
        //statement uncommented
        //however without that Hibernate knows nothing about the cascacding 
        //delete as there are no departments
        //associated with organisation as you have not added them to the list.
        organizationRepository.deleteById(organization.getId());

        assertFalse(organizationRepository.findByName(organizationName).isPresent());
        assertEquals(0, departmentRepository.findAll().size()); 
    }
}

正确的修复方法是通过封装add/remove/set操作和阻止对集合的直接访问来确保内存中的模型始终得到正确维护。例如。

public class Department(){
    public void setOrganisation(Organisation organisation){
        this.organisation = organisation;

        if(! organisation.getDepartments().contains(department)){
            organisation.addDepartment(department);
        }
    }
}

public class Organisation(){

    public List<Department> getDepartments(){
        return Collections.unmodifiableList(departments);
    }

    public void addDepartment(Department departmenmt){
        departments.add(department);

        if(department.getOrganisation() != this){
            department.setOrganisation(this);
        }
    }
}