相同表的Hibernate扩展实体

Question

我有一个包含两个字段的表，我想要两个对象。

第一个只有field1

@Entity(name = "simpleTableObject")
@Table(name = "someTable")
public class SimpleTableObject
{
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "id")
    protected long id;

    @Column(name = "field1")
    private String field1;

第二个有两个领域

@Entity(name = "tableObject")
@Table(name = "someTable")
public class TableObject
{
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "id")
    protected long id;

    @Column(name = "field1")
    private String field1;

    @Column(name = "field2")
    private String field2;

我使用加载每个

@Transactional(readOnly = true)
@SuppressWarnings("unchecked")
public List get(Class aClass)
{
    ClassMetadata hibernateMetadata = sessionFactory.getClassMetadata(aClass);
    if (hibernateMetadata == null)
    {
        return null;
    }
    if (hibernateMetadata instanceof AbstractEntityPersister)
    {
        AbstractEntityPersister persister = (AbstractEntityPersister) hibernateMetadata;
        String                  tableName = persister.getTableName();
        if (tableName != null)
        {
            return sessionFactory.getCurrentSession().
                    createQuery("from " + tableName).list();
        }
    }
    return null;
}

我想做的就是TableObject扩展SimpleTableObject。我将如何去做？

Answer 1

如果要在所需表中保存公共字段，则意味着假设您拥有A类和B类，并且具有一些通用文件（例如created_by，updated_by），并且希望将field1，field2保存在两个实体中：IN数据库级：

query> select * from A;
+----++------------------------+
| id | created_by | updated_by |
+----+------------+------------+
|  3 |    xyz     | abc        |
+----+------------+------------+
query> select * from B;
 +----++------------------------+
| id | created_by | updated_by |
+----+------------+------------+
|  3 |    xyz     | abc        |
+----+------------+------------+

对于这种类型的结构，您应该使用@MappedSuperclass，就像@Dragan Bozanovic建议的那样

但是，如果您需要“父子”关系并要为每个类生成表，则可以使用@Inheritance（strategy =
InheritanceType.TABLE_PER_CLASS）来为每个类创建表，例如：假设您有2个类Payment和CreditCard，Payment是CreditCard的父类。

@Entity
@Inheritance(strategy = InheritanceType.TABLE_PER_CLASS)
public class Payment {
    @Id
    @GeneratedValue(strategy = GenerationType.TABLE)
    private int id;
    @Column(nullable = false)
    private double amount;

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public double getAmount() {
        return amount;
    }

    public void setAmount(double amount) {
        this.amount = amount;
    }
}


@Entity
public class CreditCard extends Payment {
private String ccNumber;
private Date expireDate;

    public String getCcNumber() {
        return ccNumber;
    }

    public void setCcNumber(String ccNumber) {
        this.ccNumber = ccNumber;
    }

    public Date getExpireDate() {
        return expireDate;
    }

    public void setExpireDate(Date expireDate) {
        this.expireDate = expireDate;
    }
}

现在，您将保存日期：

public class TestConcreteClasses {
    public static void main(String[] args) {
        Payment payment = new Payment();
        payment.setAmount(52.6);
        createData(payment);
        CreditCard creditCard = new CreditCard();
        creditCard.setAmount(10);
        creditCard.setCcNumber("2536985474561236");
        creditCard.setExpireDate(new Date());
        createData(creditCard);

    }

    private static void createData(Payment instance) {
        Session session = HibernateUtil.getSession();
        session.beginTransaction();
        session.save(instance);
        session.getTransaction().commit();
    }
}

然后数据将保存为

query> select * from Payment;
+----+--------+
| id | amount |
+----+--------+
|  1 |   52.6 |
+----+--------+
1 row in set (0.00 sec)

 select * from CreditCard;
+----+--------+------------------+---------------------+
| id | amount | ccNumber         | expireDate          |
+----+--------+------------------+---------------------+
|  2 |     10 | 2536985474561236 | 2017-03-12 14:10:15 |
+----+--------+------------------+---------------------+
1 row in set (0.00 sec)

hibernate中使用了3种类型的继承，这是用于继承的hibernate文档
https://docs.jboss.org/hibernate/jpa/2.1/api/javax/persistence/InheritanceType.html，您应该根据以下条件进行选择您的要求。