我有4節課。Entry、EntryTypeOne、EntryTypeTwo 和 ExampleClass
@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;
}
當我開始這個時，我收到這個錯誤：
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
我的目標是制作這樣的資料庫： DBIMAGE
我可以在不使用 EntryTypes 實作兩個串列的情況下執行此操作嗎（1 個用于 entrytypeone，1 個用于 entrytypetwo）？
uj5u.com熱心網友回復：
您沒有@ManyToMany以正確的方式使用注釋。這就是你的方法......想象你有一個Student物體和Course物體。
學生喜歡某些課程，不喜歡其他課程。您想在資料庫中存盤有關喜歡的課程的資訊。這是你如何做...
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;
}
對于課程，你喜歡這樣......
// Just add a simple mapped by followed by the name of the field in the owning entity
@ManyToMany(mappedBy = "likedCourses")
Set<Student> likes;
這能解決您的問題嗎？在評論中告訴我。
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