java中对象的映射接口类型
我有以下代码java中对象的映射接口类型,java,jpa,hibernate-mapping,persistence.xml,Java,Jpa,Hibernate Mapping,Persistence.xml,我有以下代码 interface Loanable {} abstract class Material {} @Entity class Journal extends Material {} @Entity class Book extends Material implements Loanable {} @Entity class DigitalMedia extends Material implements Loanable {} @Entity @Table(name =
interface Loanable {}
abstract class Material {}
@Entity
class Journal extends Material {}
@Entity
class Book extends Material implements Loanable {}
@Entity
class DigitalMedia extends Material implements Loanable {}
@Entity
@Table(name = "Loan")
@Access(value = AccessType.FIELD)
public class Loan {
@Id
@Column(name="Loan_ID",updatable = false, nullable = false)
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Integer id;
@OneToOne (cascade=CascadeType.ALL)
@JoinColumn(name="studentId")
/* Person who makes the loan */
private User user;
//@Column(name="loanable")
@OneToOne (cascade=CascadeType.ALL)
@JoinColumn(name="materialId")
/* Loanble which is loaned */
private Loanable loanable;
}
如代码所示,我正在尝试将
Loan
映射到Loanable
。一个用户一次可以有一笔贷款我如何将可借阅类型对象映射到数据库?我在书籍
和数字媒体
中搜索了制作抽象类的方法并对其进行了扩展,但我无法扩展两个类,因为它们已经扩展了材料
@Convert
似乎对接口类型的对象也不起作用。我正在使用带有Hibernate持久性的JPA。JPA实体需要是类,因此尝试映射接口将不起作用。映射类不一定是具体的,因此抽象类使用关联
以下方面应起作用:
@MappedSuperclass
abstract class Material {}
@MappedSuperclass
abstract class LoanableMaterial extends Material implements Loanable {}
@Entity
class Journal extends Material {}
@Entity
class Book extends LoanableMaterial {}
@Entity
class DigitalMedia extends LoanableMaterial {}
@Entity
class Loan {
@ManyToOne(targetEntity = LoanableMaterial.class)
LoanableMaterial loaned;
}
Loan
和Loanable
之间的关联是多对多的。这是因为,尽管一次只能将一份材料借给一名学生,但它可以在不同的时间借给多名学生。同样,尽管一个学生一次只能借出一种材料,但同一个学生可以在不同的时间借出许多材料。因此,从Loan
到User
的关联也应该是manytone
。提问时,请发布代码而不是描述代码,因为从实际代码中更容易理解问题。还要确保只发布与问题相关的代码,避免发布与问题无关的任何部分。只有一些JPA提供商支持接口。听起来你的JPA提供商没有