JPA中的@MappedSuperclass

说明地址：http://docs.oracle.com/javaee/5/api/javax/persistence/MappedSuperclass.html

用来申明一个超类，继承这个类的子类映射时要映射此类中的字段，可以当做是对entity抽取封装的类。如果子类想重写此类的映射信息，可以使用 AttributeOverride and AssociationOverride annotations

Java代码

Example: Concrete class as a mapped superclass
@MappedSuperclass
public class Employee {
@Id
protected Integer empId;
@Version
protected Integer version;
@ManyToOne @JoinColumn(name="ADDR")
protected Address address;
public Integer getEmpId() { ... }
public void setEmpId(Integer id) { ... }
public Address getAddress() { ... }
public void setAddress(Address addr) { ... }
}
// Default table is FTEMPLOYEE table
@Entity
public class FTEmployee extends Employee {
// Inherited empId field mapped to FTEMPLOYEE.EMPID
// Inherited version field mapped to FTEMPLOYEE.VERSION
// Inherited address field mapped to FTEMPLOYEE.ADDR fk
// Defaults to FTEMPLOYEE.SALARY
protected Integer salary;
public FTEmployee() {}
public Integer getSalary() { ... }
public void setSalary(Integer salary) { ... }
}
@Entity @Table(name="PT_EMP")
@AssociationOverride(name="address",
joincolumns=@JoinColumn(name="ADDR_ID"))
public class PartTimeEmployee extends Employee {
// Inherited empId field mapped to PT_EMP.EMPID
// Inherited version field mapped to PT_EMP.VERSION
// address field mapping overridden to PT_EMP.ADDR_ID fk
@Column(name="WAGE")
protected Float hourlyWage;
public PartTimeEmployee() {}
public Float getHourlyWage() { ... }
public void setHourlyWage(Float wage) { ... }
}
Example: Non-entity superclass
public class Cart {
// This state is transient
Integer operationCount;
public Cart() { operationCount = 0; }
public Integer getOperationCount() { return operationCount; }
public void incrementOperationCount() { operationCount++; }
}
@Entity
public class ShoppingCart extends Cart {
Collection items = new Vector();
public ShoppingCart() { super(); }
...
@OneToMany
public Collection getItems() { return items; }
public void addItem(Item item) {
items.add(item);
incrementOperationCount();
}
}

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转载于:https://www.cnblogs.com/toSeeMyDream/p/4606896.html

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