※table per class hierarchy(每個階層類別一個表)
※table per subclass(每個子類別一個表)
※table per concrete class(每個具體類別一個表)
尤於翻譯的有和沒有一樣，所以提供官方連結，這裡先從下往上講，個人感覺比較好懂
※table per concrete class(union-subclass)
※準備資料
CREATE TABLE STUDENT( ID NUMBER(5), NAME VARCHAR(10), PRICE NUMBER(5), PRODUCT_DATE DATE, SCORE NUMBER(3), SCHOOL VARCHAR(20), CONSTRAINT PK_STUDENT PRIMARY KEY(ID) ); CREATE TABLE MAKER( ID NUMBER(5), NAME VARCHAR(10), PRICE NUMBER(5), PRODUCT_DATE DATE, SALARY NUMBER(6), COMPANY VARCHAR(20), CONSTRAINT PK_MAKER PRIMARY KEY(ID) );
※ID、NAME、PRICE、PRODUCT_DATE，這四個欄位兩張表都有，所以可以提出來模擬成java的繼承關係，取一個名字，譬如叫Chess，然後將兩張對應的表繼承它
※XML設定
Chess.java
public abstract class Chess {
private Integer id;
private String name;
private Integer price;
private Date productDate;
//setter/getter...
}
※Chess是個抽象類別，讓Student和Maker繼承
Student.java
public class Student extends Chess {
private Integer score;
private String school;
//setter/getter...
}
Maker.java
public class Maker extends Chess {
private Integer salary;
private String company;
//setter/getter...
}
Chess.hbm.xml
<class name="vo.Chess" abstract="true"> <id name="id" type="java.lang.Integer"> <column name="ID" /> <generator class="assigned" /> </id> <property name="name" type="java.lang.String"> <column name="NAME" /> </property> <property name="price" type="java.lang.Integer"> <column name="PRICE" /> </property> <property name="productDate" type="java.util.Date"> <column name="PRODUCT_DATE" /> </property> <union-subclass name="vo.Student" table="STUDENT"> <property name="score" type="java.lang.Integer"> <column name="SCORE" /> </property> <property name="school" type="java.lang.String"> <column name="SCHOOL" /> </property> </union-subclass> <union-subclass name="vo.Maker" table="MAKER"> <property name="salary" type="java.lang.Integer"> <column name="SALARY" /> </property> <property name="company" type="java.lang.String"> <column name="COMPANY" /> </property> </union-subclass> </class>
※Chess可以加個abstract=true，更加確定是個抽象類別，其他兩個類別用union-subclass
測試類：
SessionFactory sf = HibernateUtil2.getSessionFactory();
Session s1 = sf.openSession();
Session s2 = sf.openSession();
Transaction tx = s1.beginTransaction();
Transaction tx2 = s2.beginTransaction();
try {
System.out.println("-----測試學生-----");
Student stu = new Student();
stu.setId(1);
stu.setName("象棋");
stu.setPrice(50);
stu.setProductDate(new Date(100, 0, 1));
stu.setScore(78);
stu.setSchool("家裡蹲大學");
s1.save(stu);
Student stuRtn = (Student) s1.load(Student.class, 1);
System.out.println("學校名：" + stuRtn.getSchool());
System.out.println("-----測試員工-----");
Maker mak = new Maker();
mak.setId(1);
mak.setName("五子棋");
mak.setPrice(30);
mak.setProductDate(new Date(102, 11, 12));
mak.setSalary(43000);
mak.setCompany("少林寺管委會");
s2.save(mak);
Maker makRtn = (Maker) s2.load(Maker.class, 1);
System.out.println("公司名：" + makRtn.getCompany());
tx.commit();
tx2.commit();
} catch (Exception e) {
System.err.println("例外錯誤！");
e.printStackTrace();
tx.rollback();
} finally {
if (s1.isOpen()) {
s1.close();
}
if (s2.isOpen()) {
s2.close();
}
}
※hibernate.cfg.xml只要增加一行<mapping resource="vo/Chess.hbm.xml" />即可
※如果使用同一個session，而且id相同，就會出現「org.hibernate.NonUniqueObjectException: a different object with the same identifier value was already associated with the session:」的例外
就算有二級快取，也是一樣，所以和快取沒關係
．原因是因為同一個session不能有相同的名稱
．使用Session的clean、refresh、merge都不行
．但如果是Student和Maker分開，也就是Student做完就commit，然後clean再做Maker即可，我現在是假設二筆資料一起commit、一起rollback的話就不行
．Maker不使用save，改用merge會過，但在load時，會出現Student不能強轉成Maker的錯，很正常，因為繼承同一個類別，Session裡面存的是第一次的Student
．這是使用table per concrete class的缺點
※Annotation設定
Chess.java
@Inheritance(strategy = InheritanceType.TABLE_PER_CLASS)
@Entity
public abstract class Chess {
private Integer id;
private String name;
private Integer price;
private Date productDate;
@Id
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public Integer getPrice() {
return price;
}
public void setPrice(Integer price) {
this.price = price;
}
@Column(name = "PRODUCT_DATE")
public Date getProductDate() {
return productDate;
}
public void setProductDate(Date productDate) {
this.productDate = productDate;
}
}
※id是一定要設的，而Column只有productDate的名稱和資料庫不同，設這個就好
※三個類別都必需設定@Inheritance
Student.java
@Inheritance(strategy = InheritanceType.TABLE_PER_CLASS)
@Entity
public class Student extends Chess {
private Integer score;
private String school;
//setter/getter...
}
※由於Table和Column一樣可以不打，所以這是最精簡設定
Maker.java
@Inheritance(strategy = InheritanceType.TABLE_PER_CLASS)
@Entity
public class Maker extends Chess {
private Integer salary;
private String company;
//setter/getter...
}
hibernate.cfg.xml
<mapping class="vo.Chess" /> <mapping class="vo.Student" /> <mapping class="vo.Maker" />
※三個類別都必需增加才可以
※測試類別一樣
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