java - 如何坚持涉及@JoinFormula 的逆@OneToOne 映射？

Question

我正在尝试在 Hibernate 中映射以下表之间的关系:

create table binary (
    id number not null primary key,
    data blob,
    entity_class varchar(255) not null,
    entity_id number not null,
    unique (entity_id, entity_class)
);

create table container_entity (
    id number not null primary key,
    ...
);

二进制表应该保存任意其他表的二进制数据，“外键” - 虽然不是数据库术语 - 由 binary.entity_class 和 binary.entity_id< 组成。这是我现在必须接受的结构，它似乎在这里引起了困惑。 binary.entity_id 列引用聚合表的主键，而 binary.entity_class 定义聚合表本身:

BINARY                               CONTAINER_ENTITY_A  CONTAINER_ENTITY_B 
id  entity_class      entity_id      id                  id                    ...
-------------------------------      ------------------  ------------------
1   ContainerEntityA  1          ->  1                                         ...
2   ContainerEntityB  1          ->                      1
3   ContainerEntityB  2          ->                      2

当以只读方式使用时，ContainerEntity 中的映射已经可以找到:

@Entity @Table(name="container_entity_a")
public class ContainerEntityA {
  @Id @GeneratedValue(strategy = GenerationType.AUTO)
  private Long id;

  @OneToOne
  @JoinColumnsOrFormulas({ 
    @JoinColumnOrFormula(column = 
      @JoinColumn(name = "id", referencedColumnName = "entity_id", 
        insertable=false, updatable=false)),
    @JoinColumnOrFormula(formula = 
      @JoinFormula(value = "'ContainerEntityA'", referencedColumnName = "entity_class")) 
  })
  private Binary binary;

  public void setBinary(Binary aBinary) {
    aBinary.setEntityClass("ContainerEntityA");
    this.binary = aBinary;
  }
}

@Entity @Table(name="binary")
public class Binary {
  @Column(name = "entity_id", nullable = false)
  private Long entityId;

  @Column(name = "entity_class", nullable = false)
  private String entityClass;
}

但是我在持久化 ContainerEntity 时遇到了问题:

• 如果我只指定 CascadeType.PERSIST，Hibernate 无法设置 binary.entity_id。

• 如果我不使用 cascade-persist，我不知道什么时候自己设置 binary.entity_id，如何持久化映射对象，我最终得到:

  org.hibernate.TransientObjectException:对象引用未保存的 transient 实例 - 在刷新之前保存 transient 实例:ContainerEntity.binary -> Binary

换句话说，我希望但目前无法像这样持久化这两个实体:

containerEntity = new ContainerEntity();
containerEntity.setBinary( new Binary() );
entityManager.persist(containerEntity);

有什么想法或有用的建议吗？

---

赏金注意事项:这个问题还没有我可以接受为“正确”的答案，尽管还有一个提示我会在下周检查。不过，我的赏金时间已经结束，所以我会将它奖励给目前最接近的答案。

Answer 1

好的，请尝试以下我认为完美的方法。我已经测试并且可以按预期加载和保存容器和关联实体。

首先，容器必须从一些通用实体扩展:

@Entity
@Inheritance(strategy = InheritanceType.TABLE_PER_CLASS)
public abstract class Container {

    //cannot use identity here however a table or sequence should work so long as
    //the initial value is > current max ids from all container tables.
    @Id
    @TableGenerator(initialValue = 10000, allocationSize = 100, table = "id_gen", name = "id_gen")
    @GeneratedValue(strategy = GenerationType.TABLE, generator = "id_gen")
    private Long id;

    public Long getId() {
        return id;
    }

    public BinaryData getBinaryData() {
        return getData().size() > 0 ? getData().get(0) : null;
    }

    public void setBinaryData(BinaryData binaryData) {
        binaryData.setContainerClass(getName());
        binaryData.setContainer(this);

        this.getData().clear();
        this.getData().add(binaryData);
    }

    protected abstract List<BinaryData> getData();

    protected abstract String getName();
}

混凝土容器A.该关系必须映射为 OneToMany，但是附加的 @Where 子句(以及您的数据库唯一键)有效地使其成为 @OneToOne。此类的客户可以将其视为单端关联:

@Entity
@Table(name = "container_a")
public class ContainerA extends Container {

    @OneToMany(mappedBy = "container", cascade = CascadeType.ALL)
    @Where(clause = "container_class = 'container_a'")
    private List<BinaryData> binaryData;

    public ContainerA() {
        binaryData = new ArrayList<>();
    }

    @Override
    protected List<BinaryData> getData() {
        return binaryData;
    }

    @Override
    protected String getName() {
        return "container_a";
    }
}

容器B

@Entity
@Table(name = "container_b")
public class ContainerB extends Container {

    @OneToMany(mappedBy = "container", cascade = CascadeType.ALL)
    @Where(clause = "container_class = 'container_b'")
    private List<BinaryData> binaryData;

    public ContainerB() {
        binaryData = new ArrayList<>();
    }

    @Override
    protected List<BinaryData> getData() {
        return binaryData;
    }

    @Override
    protected String getName() {
        return "container_b";
    }
}

从 BinaryData 映射回 Container 需要使用 Hibernate 的 @Any 映射。

@Entity
@Table(name = "binary_data")
public class BinaryData {

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

    @OneToOne
    @Any(metaColumn = @Column(name = "container_class"))
    @AnyMetaDef(idType = "long", metaType = "string", metaValues = {
            @MetaValue(targetEntity = ContainerA.class, value = "container_a"),
            @MetaValue(targetEntity = ContainerB.class, value = "container_b") })
    @JoinColumn(name = "entity_id")
    private Container container;

    @Column(name = "container_class")
    private String containerClass;

    public Long getId() {
        return id;
    }

    public Container getContainer() {
        return container;
    }

    public void setContainer(Container container) {
        this.container = container;
    }

    public String getContainerClass() {
        return containerClass;
    }

    public void setContainerClass(String containerClass) {
        this.containerClass = containerClass;
    }
}

以下测试按预期通过:

public class ContainerDaoTest extends BaseDaoTest {

    @Test
    public void testSaveEntityA() {

        ContainerA c = new ContainerA();

        BinaryData b = new BinaryData();
        c.setBinaryData(b);

        ContainerDao dao = new ContainerDao();
        dao.persist(c);

        c = dao.load(c.getId());
        Assert.assertEquals(c.getId(), b.getContainer().getId());
    }

    @Test
    public void testLoadEntity() {
        ContainerA c = new ContainerDao().load(2l);
        Assert.assertEquals(new Long(3), c.getBinaryData().getId());
        Assert.assertEquals(new Long(2), c.getBinaryData().getContainer().getId());
        Assert.assertEquals("container_a", c.getBinaryData().getContainerClass());
    }

    @Override
    protected String[] getDataSetPaths() {
        return new String[] { "/stack/container.xml", "/stack/binarydata.xml" };
    }
}

使用以下数据集时:

<dataset>
    <container_a id="1" />
    <container_a id="2" />
    <container_b id="1" />
    <container_b id="2" />
</dataset>

<dataset>
    <binary_data id="1" container_class="container_a" entity_id="1" />
    <binary_data id="2" container_class="container_b" entity_id="2" />
    <binary_data id="3" container_class="container_a" entity_id="2" />
    <binary_data id="4" container_class="container_b" entity_id="1" />
</dataset>