Java – @ manytoone mapping is not applicable to connection inheritance
I have the following database structure:
CREATE TABLE `author` ( `id` int(10) unsigned NOT NULL AUTO_INCREMENT,`name` varchar(255) NOT NULL,`email` varchar(255) NOT NULL,`password` varchar(255) NOT NULL,PRIMARY KEY (`id`)); CREATE TABLE `message` ( `id` int(10) unsigned NOT NULL AUTO_INCREMENT,`title` varchar(500) NOT NULL,`text` varchar(50000) NOT NULL,`author_id` int(10) unsigned DEFAULT NULL,`creation_date` datetime NOT NULL,`last_update_date` datetime NOT NULL,PRIMARY KEY (`id`),KEY `author_id_fk` (`author_id`),CONSTRAINT `message_ibfk_1` FOREIGN KEY (`author_id`) REFERENCES `author` (`id`)); CREATE TABLE `comment` ( `id` int(10) unsigned NOT NULL,`post_id` int(10) unsigned NOT NULL,KEY `message_id_fk` (`id`),KEY `post_id_fk` (`post_id`),CONSTRAINT `comment_ibfk_1` FOREIGN KEY (`id`) REFERENCES `message` (`id`),CONSTRAINT `comment_ibfk_2` FOREIGN KEY (`post_id`) REFERENCES `post` (`id`)); CREATE TABLE `post` ( `id` int(10) unsigned NOT NULL,CONSTRAINT `post_ibfk_1` FOREIGN KEY (`id`) REFERENCES `message` (`id`) ON DELETE CASCADE);
And the following mapping using hibernate (3.5.4-final):
@Entity @Table(name = "author") public class Author { private Long id = 0L; private String name; private String email; private String password; private Set<Post> posts; private Set<Comment> comments; @Id @Column(name = "id") @GeneratedValue public Long getId() { return id; } public void setId(Long id) { this.id = id; } @Column(name = "name") public String getName() { return name; } public void setName(String name) { this.name = name; } @Column(name = "email") public String getEmail() { return email; } public void setEmail(String email) { this.email = email; } @Column(name = "password") public String getpassword() { return password; } public void setPassword(String password) { this.password = password; } @OneToMany(mappedBy = "author") public Set<Post> getPosts() { return posts; } public void setPosts(Set<Post> posts) { this.posts = posts; } @OneToMany(mappedBy = "author") public Set<Comment> getComments() { return comments; } public void setComments(Set<Comment> comments) { this.comments = comments; } } @MappedSuperclass @Table(name = "message") @Inheritance(strategy = InheritanceType.JOINED) public abstract class Message implements Serializable { private Long id; private String title; private String text; private Author author; private Date creationDate; private Date lastUpdateDate; @Id @Column(name = "id") @GeneratedValue public Long getId() { return id; } public void setId(Long id) { this.id = id; } @Column(name = "title") public String getTitle() { return title; } public void setTitle(String title) { this.title = title; } @Column(name = "text") public String getText() { return text; } public void setText(String text) { this.text = text; } @ManyToOne @JoinColumn(name = "author_id") public Author getAuthor() { return author; } public void setAuthor(Author author) { this.author = author; } @Column(name = "creation_date") public Date getCreationDate() { return creationDate; } public void setCreationDate(Date creationDate) { this.creationDate = creationDate; } @Column(name = "last_update_date") public Date getLastUpdateDate() { return lastUpdateDate; } public void setLastUpdateDate(Date lastUpdateDate) { this.lastUpdateDate = lastUpdateDate; } } @Entity @Table(name = "comment") @PrimaryKeyJoinColumn(name="id") public class Comment extends Message { private static final long serialVersionUID = 1L; private Post post; @ManyToOne @JoinColumn(name = "post_id") public Post getPost() { return post; } public void setPost(Post post) { this.post = post; } } @Entity @Table(name = "post") @PrimaryKeyJoinColumn(name="id") public class Post extends Message { private static final long serialVersionUID = 1L; private Set<Comment> comments; @OneToMany(mappedBy = "post") public Set<Comment> getComments() { return comments; } public void setComments(Set<Comment> comments) { this.comments = comments; } }
The main idea is that both comment and post inherit from message. I hope they have a two-way relationship But when I run the following code:
Session session = HibernateUtil.getSessionFactory().getCurrentSession(); Transaction tx = session.beginTransaction(); Author author = new Author(); author.setName("mike"); author.setPassword("123"); author.setEmail("mike@gmail.com"); Post post = new Post(); post.setAuthor(author); post.setCreationDate(new Date()); post.setLastUpdateDate(new Date()); post.setText("Text"); post.setTitle("Title"); Long authorId = (Long)session.save(author); Long postId = (Long)session.save(post); tx.commit();
I received the following error:
ERROR JDBCExceptionReporter:101 - UnkNown column 'author_id' in 'field list' Exception in thread "main" org.hibernate.exception.sqlGrammarException: Could not insert: [org.blogsample.mappingbeans.Post] at org.hibernate.exception.sqlStateConverter.convert(sqlStateConverter.java:92) at org.hibernate.exception.JDBCExceptionHelper.convert(JDBCExceptionHelper.java:66) at org.hibernate.id.insert.AbstractReturningDelegate.performInsert(AbstractReturningDelegate.java:64)
Update as @ JB nizet mentioned earlier, I changed @ mappedsuperclass to @ entity, and then I got another error. Mappedby refers to an unknown target entity attribute: org blogsample. mappingbeans. Comment. Author, which is solved by changing the DB structure (deleting the author_id) from the message table, adding it to each comment, publishing and creating the foreign key of this column) and moving the author (and getter / setter with mapping) to the comment and post classes
Solution
Your message class should not use the @ mappedsuperclass annotation, but the @ entity annotation@ Mappedsuperclass means that the entity extending this class inherits columns and associations from the superclass, but these columns and associations are in the table of the subclass author_ ID is not in comment table or post table It is in the message table
And @ table can only be used with entities It is not a mapped superclass. It is only used to inherit fields and associations, but it is not mapped to its own table like an entity