Hibernate 与继承的关系

Question

我有 4 个类。条目、条目类型一、条目类型二和示例类

@Getter
@Setter
@Entity
@Inheritance(strategy = InheritanceType.SINGLE_TABLE)
@DiscriminatorColumn(name="entryType",
        discriminatorType = DiscriminatorType.STRING)
public class Entry {
    @Id
    @GeneratedValue
    protected Long id;

    @Column(nullable = false)
    protected String title;

    @Column(nullable = false)
    protected String description;
}

@Getter
@Setter
@Entity
@DiscriminatorValue("One")
public class EntryTypeOne extends Entry{

    @ManyToMany(cascade = CascadeType.ALL)
    private List<ExampleClass> exampleClasses;
}

@Getter
@Setter
@Entity
@DiscriminatorValue("Two")
public class EntryTypeTwo extends Entry{

    @ManyToMany(cascade = CascadeType.ALL)
    private List<ExampleClass> exampleClasses;
}

@Getter
@Setter
@Entity
public class ExampleClass {

    @Id
    @GeneratedValue
    private Long id;

    @ManyToMany(mappedBy = "exapmleClasses")
    private List<Entry> entries;
}

当我开始这个时，我得到这个错误：

nested exception is org.hibernate.AnnotationException: mappedBy reference an unknown target entity property: ch.musiciansearch.vingrn.entity.Entry.exampleClasses in ch.musiciansearch.vingrn.entity.ExampleClass.entries

我的目标是制作这样的数据库： DBIMAGE

我可以在不使用 EntryType 实现两个列表的情况下执行此操作吗（1 个用于 entrytypeone，1 个用于 entrytypetwo）？

Answer 1

您没有以正确的方式使用 @ManyToMany 注释。这是您的操作方式...假设您有一个 Student 实体和 Course 个实体。

而且学生喜欢一些课程，不喜欢其他课程。您想要在数据库中存储有关喜欢的课程的信息。这是你的做法...

class Student {

// OK, so student class will be the owner of the relationship
// Here we describe the join table, which stores many-to-many data in the DB
@ManyToMany
@JoinTable(
  name = "course_like", 
  joinColumns = @JoinColumn(name = "student_id"), 
  inverseJoinColumns = @JoinColumn(name = "course_id"))
Set<Course> likedCourses;
}

当然 class 你喜欢这样...

// Just add a simple mapped by followed by the name of the field in the owning entity
@ManyToMany(mappedBy = "likedCourses")
Set<Student> likes;

这是否解决了您的问题？在评论中让我知道。

Hibernate 与继承的关系

Hibernate Relationships with inheritance

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inheritance

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