如何让 Hibernate JPA 自动管理列表索引？

Question

如何使用列表设置基本的一对多关系并让 Hibernate JPA 自动管理列表的序列索引号？这可以做到吗？

这是我的测试用例（或多或少）；

@Table(name="Policy_Root")
public class PolicyRoot extends BaseDomainModel {

    private List<Policy> policyList = new ArrayList<Policy>();

    @OneToMany(targetEntity=Policy.class, mappedBy="policyRoot", cascade=CascadeType.ALL)
    @IndexColumn(name="policy_sequence", base=0, nullable=false)
    public List<Policy> getPolicyList() {
        return policyList;
    }

    public void setPolicyList(List<Policy> policyList) {
        this.policyList = policyList;
    }

    public void addPolicy(Policy policy) {
        policyList.add(policy);
        policy.setPolicyRoot(this);
    }

    public void addPolicy(int sequence, Policy policy) {
        policyList.add(sequence, policy);
        policy.setPolicyRoot(this);
    }
}

@Entity()
@Table(name="Policy")
public class Policy extends BaseDomainModel {

    /** The position of this policy record within the list of policy's belong to the parent PolicyRoot    */
    private int policySequence;

    /** Birectional pointer to parent */
    private PolicyRoot policyRoot;

    @Column(name="policy_sequence")
    public int getPolicySequence() {
        return policySequence;
    }

    public void setPolicySequence(int policySequence) {
        this.policySequence = policySequence;
    }

    @ManyToOne
    @JoinColumn(name="policy_root_oid", nullable=false)
    public PolicyRoot getPolicyRoot() {
        return policyRoot;
    }

    public void setPolicyRoot(PolicyRoot policyRoot) {
        this.policyRoot = policyRoot;
    }
}


    @Test
    public void testCreation() {
        Policy policy1 = new Policy();
        Policy policy2 = new Policy();

        // Uncomment the following and the test case works - but I don't want to manage the sequence numbers
        //policy2.setPolicySequence(1);

        PolicyRoot policyRoot = new PolicyRoot();
        policyRoot.addPolicy(policy1);
        policyRoot.addPolicy(policy2);

        ServiceImplFacade.getPersistenceFacade().persistSingleItem(policyRoot);
        Long oid = policyRoot.getOid();
        PolicyRoot policyRootFromDB = ServiceImplFacade.getPersistenceFacade().getEntityManager().find(PolicyRoot.class, oid);

        assertEquals(2, policyRootFromDB.getPolicyList().size());
    }

如果我取消注释policy2.setPolicySequence(1);行然后测试用例通过，但我认为我不需要这样做。我希望 Hibernate 为我做这件事。我的理解是它可以，但如果它不能，那么知道它不能也是一个很好的答案。

我尝试过设置可为空、可插入和可更新的各种组合，但我可能错过了其中一种。

这可能吗？ - 如果是这样怎么办？

Answer 1

找到了答案——它是关于获得可为空和可插入的正确组合。还必须在 Integer 处创建“子索引”，以便它可以为空，并且下面还有一个“可选”标志。

public class PolicyRoot extends BordereauxBaseDomainModel {

     private List<Policy> policyList = new ArrayList<Policy>();

    @OneToMany(cascade=CascadeType.ALL)
    @IndexColumn(name="policy_sequence", nullable=false, base=0)
    @JoinColumn(name="policy_root_oid", nullable=false)
    public List<Policy> getPolicyList() {
        return policyList;
    }

    public void setPolicyList(List<Policy> policyList) {
        this.policyList = policyList;
    }
}


public class Policy extends BordereauxBaseDomainModel {

    /** The position of this policy record within the list of policy's belong to the parent PolicyRoot    */
    private Integer policySequence;

    /** Birectional pointer to parent */
    private PolicyRoot policyRoot;

    @Column(name="policy_sequence", insertable=false, updatable=false)
    public Integer getPolicySequence() {
        return policySequence;
    }

    public void setPolicySequence(Integer policySequence) {
        this.policySequence = policySequence;
    }

    @ManyToOne(optional=false)
    @JoinColumn(name="policy_root_oid", insertable=false, updatable=false, nullable=false)
    public PolicyRoot getPolicyRoot() {
        return policyRoot;
    }

    public void setPolicyRoot(PolicyRoot policyRoot) {
        this.policyRoot = policyRoot;
    }
}

在谷歌搜索了一段时间后，在下一页找到了答案。

http://opensource.atlassian.com/projects/hibernate/browse/HHH- 4390

Answer 2

做这样的事情：

@Entity
class Parent {

    @OneToMany
    @IndexColumn(name = "index_column")
    List<Child> children;
}

@Entity
class Child {

    @ManyToOne
    Parent parent;
    @Column(name = "index_column")
    Integer index;

    @PrePersist
    @PreUpdate
    private void prepareIndex() {
        if (parent != null) {
            index = parent.children.indexOf(this);
        }
    }
}

Answer 3

我将发布这个答案，因为我最近遇到了同样的问题，并且这个问题虽然已经过时，但在研究中不断出现。

@IndexColumn 注释已弃用很久以前。事实上，实际上建议使用 @OrderColumn 注释代替。第二个注释不仅简化了语法而不必指定 base 属性，而且还避免了在详细信息类中声明额外的字段（policySequence 字段在详细信息类中）在本例中为 >Policy 类）。这是因为，有了@OrderColumn注解，Hibernate会自动理解在Policy表中声明一个字段，并用注解的属性name来命名它。并使用对象在列表中覆盖的索引对其进行初始化。

这是之前代码片段的更新版本：

@Table(name = "Policy_Root")
public class PolicyRoot extends BaseDomainModel {

    private List<Policy> policyList = new ArrayList<Policy>();

    @OneToMany(targetEntity = Policy.class, mappedBy = "policyRoot", cascade = CascadeType.ALL)
    @OrderColumn(name = "policy_sequence", nullable = false)
    public List<Policy> getPolicyList() {
        return policyList;
    }

    public void setPolicyList(List<Policy> policyList) {
        this.policyList = policyList;
    }

    public void addPolicy(Policy policy) {
        policyList.add(policy);
        policy.setPolicyRoot(this);
    }

    public void addPolicy(int sequence, Policy policy) {
        policyList.add(sequence, policy);
        policy.setPolicyRoot(this);
    }
}

@Entity()
@Table(name = "Policy")
public class Policy extends BaseDomainModel {

    //No need to declare the policySequence field

    /** Birectional pointer to parent */
    private PolicyRoot policyRoot;

    @ManyToOne
    @JoinColumn(name="policy_root_oid", nullable=false)
    public PolicyRoot getPolicyRoot() {
        return policyRoot;
    }

    public void setPolicyRoot(PolicyRoot policyRoot) {
        this.policyRoot = policyRoot;
    }
}