I've been struggling to make a many to many relationship with an additional column in the link table.
These are my entities:
@JsonIgnoreProperties({ "hibernateLazyInitializer", "handler" })
public class Post {
@Id
@GeneratedValue
private Long id;
private String name;
@OneToMany(mappedBy = "post", cascade = CascadeType.ALL, orphanRemoval = true)
@JsonIgnore
private List<PostTag> tags = new ArrayList<>();
//getters and setters
public void addTag(Tag tag){
PostTag postTag = new PostTag(this, tag);
tags.add(postTag);
tag.getPosts().add(postTag);
}
public void removeTag(Tag tag) {
for (Iterator<PostTag> iterator = tags.iterator();
iterator.hasNext(); ) {
PostTag postTag = iterator.next();
if (postTag.getPost().equals(this) &&
postTag.getTag().equals(tag)) {
iterator.remove();
postTag.getTag().getPosts().remove(postTag);
postTag.setPost(null);
postTag.setTag(null);
}
}
}
@Override
public boolean equals(Object o) {
if (this == o)
return true;
if (o == null || getClass() != o.getClass())
return false;
Post post = (Post) o;
return id == post.id;
}
@Override
public int hashCode() {
return Objects.hash(id);
}
}
@JsonIgnoreProperties({ "hibernateLazyInitializer", "handler" })
public class Tag {
@Id
@GeneratedValue
private Long id;
private String comment;
@OneToMany(mappedBy = "tag", cascade = CascadeType.ALL, orphanRemoval = true)
@JsonIgnore
private List<PostTag> posts = new ArrayList<>();
//getters and setters
@Override
public boolean equals(Object o) {
if (this == o)
return true;
if (o == null || getClass() != o.getClass())
return false;
Tag that = (Tag) o;
return id == that.id;
}
@Override
public int hashCode() {
return Objects.hash(id);
}
}
@Entity(name = "PostTag")
@Table(name = "post_tag")
@JsonIgnoreProperties({ "hibernateLazyInitializer", "handler" })
public class PostTag {
@EmbeddedId
private PostTagId id;
@ManyToOne(fetch = FetchType.LAZY)
@MapsId("postId")
private Post post;
@ManyToOne(fetch = FetchType.LAZY)
@MapsId("tagId")
private Tag tag;
private Integer impact;
public FacilityParticipant(Post post, Tag tag) {
this.post = post;
this.tag = tag;
this.id = new PostTagId(post.getId(), tag.getId());
}
//getters and setters
@Override
public boolean equals(Object o) {
if (this == o)
return true;
if (o == null || getClass() != o.getClass())
return false;
PostTag that = (PostTag) o;
return Objects.equals(post, that.post) && Objects.equals(tag, that.tag);
}
@Override
public int hashCode() {
return Objects.hash(post, tag);
}
}
@Embeddable
public class PostTagId implements Serializable {
private Long postId;
private Long tagId;
//getters setters
@Override
public boolean equals(Object o) {
if (this == o)
return true;
if (o == null || getClass() != o.getClass())
return false;
PostTagId that = (PostTagId) o;
return Objects.equals(postId, that.postId) && Objects.equals(tagId, that.tagId);
}
@Override
public int hashCode() {
return Objects.hash(postId, tagId);
}
}
I have a post entity that is mapped to many tags and a tag that is mapped to many posts. The link table is PostTag which contains the mappings to both sides, and the additional column, "impact". The PK of the link table is mapped to an Embeddable table PostTagId, which contains the PK from Post and Tag.
When I try to insert new entities, I do the following:
Tag tag1 = new Tag();
Tag tag2 = new Tag();
repository.save(tag1);
repository.save(tag2);
Post post1 = new Post();
Post post2 = new Post();
post1.addTag(tag1);
post1.addTag(tag2);
post2.addTag(tag1);
repository.save(post1);
repository.save(post2);
When trying to insert these items, I get the error that I cannot insert NULL into ("POST_TAG"."ID")
Anything that I've tried, it either comes with other errors, or it gets right back at it.
Most probably something from the model is not right, but I really cannot figure what is wrong with it.
The whole modelling was based on this article The best way to ...
Any help would be really appreciated.
Thanks
See Question&Answers more detail:os