javax.persistence Annotation MappedSuperclass
javax.persistence Annotation MappedSuperclass
恋空御月 发表于5个月前
javax.persistence Annotation MappedSuperclass
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Designates a class whose mapping information is applied to the entities that inherit from it.

指定一个类,其映射信息应用于从它继承的实体。

A mapped superclass has no separate table defined for it.

一个父类没有单独的表映射为它定义。

A class designated with the MappedSuperclass annotation can be mapped in the same way as an entity except that the mappings will apply only to its subclasses since no table exists for the mapped superclass itself.

一个指定MappedSuperclass注解的类可以以同样的方式映射为一个实体除了映射将只适用于它的子类之外因为父类本身的自映射不存在表。

When applied to the subclasses the inherited mappings will apply in the context of the subclass tables. Mapping information may be overridden in such subclasses by using the AttributeOverride and AssociationOverride annotations or corresponding XML elements.

当应用到子类时,继承的映射将应用于子类表的上下文中。
映射信息可以重写,这样子用attributeoverride和associationoverride注释或相应的XML元素。

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) { ... }
    }

 

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