Question

我正在尝试使用JPA注释在Hibernate中使用JOINED继承策略。 My Base类是抽象的，与其他实体具有多对一关联。但是我得到了Hibernate Exception：无法实例化抽象类或接口。以下是我的班级结构：

Account.java

@Entity(name="BANK_ACCOUNTS")
@Inheritance(strategy=InheritanceType.JOINED)
public abstract class Account {

    @Id
    @Column(name="ACC_ID")
    @SequenceGenerator(name="account_id_seq", sequenceName="BANK_ACCOUNT_ACC_ID", allocationSize=1)
    @GeneratedValue(strategy=GenerationType.SEQUENCE, generator="account_id_seq")
    private Long id;

    @Column(name="IS_ACTIVE")
    @Type(type="yes_no")
    private Boolean isActive;

    @ManyToOne(fetch=FetchType.LAZY)
    @JoinColumn(name="ACC_BRANCH_ID")
    private Branch branch;
}

SavingsAccount.java

@Entity(name="BANK_SAVINGS_ACCOUNT")
public class SavingsAccount extends Account{

    @Column(name="CURR_BAL")
    private BigDecimal currentBalance;
}

Branch.class

@Entity(name="BANK_BRANCH")
public class Branch {

    @Id
    @Column(name="BRANCH_ID")
    @SequenceGenerator(name="branch_id_seq", sequenceName="BANK_BRANCH_BRANCH_ID", allocationSize=1)
    @GeneratedValue(strategy=GenerationType.SEQUENCE, generator="branch_id_seq")
    private Long id;


    @OneToMany(mappedBy="branch",orphanRemoval=true, fetch= FetchType.LAZY)
    @Cascade(value=org.hibernate.annotations.CascadeType.ALL)
    private Set<Account> accounts = new HashSet<Account>(); 
}

因此，每当我尝试使用以下代码获取分支持有的帐户列表时，我会得到下面提到的异常：

Branch branch = (Branch) session.get(Branch.class, branchId);
SavingsAccount acc = new SavingsAccount();
acc.setBranch(branch);
branch.getAccounts().add(acc);

异常追踪：

org.hibernate.InstantiationException: Cannot instantiate abstract class or interface:  : com.sapient.bank.entities.Account
    at org.hibernate.tuple.PojoInstantiator.instantiate(PojoInstantiator.java:114)
    at org.hibernate.tuple.PojoInstantiator.instantiate(PojoInstantiator.java:136)
    at org.hibernate.tuple.entity.AbstractEntityTuplizer.instantiate(AbstractEntityTuplizer.java:737)
    at org.hibernate.persister.entity.AbstractEntityPersister.instantiate(AbstractEntityPersister.java:4761)
    at org.hibernate.internal.SessionImpl.instantiate(SessionImpl.java:1427)
    at org.hibernate.internal.SessionImpl.instantiate(SessionImpl.java:1415)
    at org.hibernate.loader.plan.exec.process.internal.EntityReferenceInitializerImpl.hydrateEntityState(EntityReferenceInitializerImpl.java:235)
    at org.hibernate.loader.plan.exec.process.internal.AbstractRowReader.readRow(AbstractRowReader.java:107)
    at org.hibernate.loader.plan.exec.process.internal.ResultSetProcessorImpl.extractResults(ResultSetProcessorImpl.java:129)
    at org.hibernate.loader.plan.exec.internal.AbstractLoadPlanBasedLoader.executeLoad(AbstractLoadPlanBasedLoader.java:138)
    at org.hibernate.loader.plan.exec.internal.AbstractLoadPlanBasedLoader.executeLoad(AbstractLoadPlanBasedLoader.java:102)
    at org.hibernate.loader.collection.plan.AbstractLoadPlanBasedCollectionInitializer.initialize(AbstractLoadPlanBasedCollectionInitializer.java:100)
    at org.hibernate.persister.collection.AbstractCollectionPersister.initialize(AbstractCollectionPersister.java:693)
    at org.hibernate.event.internal.DefaultInitializeCollectionEventListener.onInitializeCollection(DefaultInitializeCollectionEventListener.java:92)
    at org.hibernate.internal.SessionImpl.initializeCollection(SessionImpl.java:1933)
    at org.hibernate.collection.internal.AbstractPersistentCollection$4.doWork(AbstractPersistentCollection.java:559)
    at org.hibernate.collection.internal.AbstractPersistentCollection.withTemporarySessionIfNeeded(AbstractPersistentCollection.java:261)
    at org.hibernate.collection.internal.AbstractPersistentCollection.initialize(AbstractPersistentCollection.java:555)
    at org.hibernate.collection.internal.AbstractPersistentCollection.read(AbstractPersistentCollection.java:143)
    at org.hibernate.collection.internal.AbstractPersistentCollection$3.doWork(AbstractPersistentCollection.java:336)
    at org.hibernate.collection.internal.AbstractPersistentCollection$3.doWork(AbstractPersistentCollection.java:324)
    at org.hibernate.collection.internal.AbstractPersistentCollection.withTemporarySessionIfNeeded(AbstractPersistentCollection.java:261)
    at org.hibernate.collection.internal.AbstractPersistentCollection.readElementExistence(AbstractPersistentCollection.java:323)
    at org.hibernate.collection.internal.PersistentSet.add(PersistentSet.java:200)
    at com.sapient.bank.dao.AccountDao.createNewSavingsAcc(AccountDao.java:28)
    at com.sapient.util.MainClass.main(MainClass.java:32)

请帮我理解我的代码有什么问题。如果我删除抽象关键字，它的工作正常，但我想使Account类成为抽象。有没有办法实现这个目标？

Answer 1

如果您希望允许 SavingsAccount 或子女的SavingsAccount ，您可以在分支实体中尝试以下语法：

{% block body %}
    {% if movies|length == 0 %}
        There are no movie items available. Add a movie <a href="{{ path('movie_create_form') }}">here</a> to get started.
    {% elseif movies|length != 0 %}
        These are the results: <br />
        <ul>
            {% for x in movies %}
                <li>Title: {{ x.title }}  - Price: {{ x.price }} - <a href="{{ path('movie_edit', {id: x.id}) }}">Edit</a> - <a href="{{ path('movie_details', { id: x.id }) }}">Details</a> - <a href="{{ path('movie_delete', {id: x.id}) }}"> Delete</a></li>
            {% endfor %}
        </ul>
        <a href="{{ path('movie_create_form') }}">Add more movie entries</a>
    {% endif %}
{% endblock %}

如果您想要添加所有未来的帐户子对象，那么

 @Cascade(value=org.hibernate.annotations.CascadeType.ALL)
 private Set<? extends Account> accounts = new HashSet<SavingsAccount>();

Answer 2

您应该将Account课程设为MappedSuperclass而不是Entity。我没有尝试过，所以请告诉我，但这就是你如何处理带有JPA注释的抽象类。

参考：The Java EE 6 Tutorial : Entity Inheritance

Hibernate：获取org.hibernate.InstantiationException同时在onetomany关联中获取多态集合

2 个答案: