Many to Many relation with embedded key is inserting null in primary key

Question

Facing problem inserting records in intermediate table. Post and Tag tables are sharing many to many relationship using intermediate table post_tag;

Post table: id (pk), post, created_by, created_on, modified_by, modified_on

Tag table: id (pk), tag, created_by, created_on, modified_by, modified_on

Post_Tag table: post_id, tag_id (pk post_id and tag_id), created_by, created_on, modified_by, modified_on

Entities:

// ID class
@Embeddable @Data @NoArgsConstructor @AllArgsConstructor
public class PostTagId
    implements Serializable {
 
    @Column(name = "post_id")
    private Long postId;
 
    @Column(name = "tag_id")
    private Long tagId;
}

@Entity
@Table(name = "post_tag")
@EntityListeners(AuditingEntityListener.class)
@Data
@EqualsAndHashCode(callSuper = false)
public class PostTag extends Auditable<String> {
 
    @EmbeddedId
    private PostTagId id;
 
    @ManyToOne
    @MapsId("postId")
    @JoinColumn(name="post_id")
    private Post post;
 
    @ManyToOne
    @MapsId("tagId")
    @JoinColumn(name="tag_id")
    private Tag tag;
 
    public PostTag(Post post, Tag tag) {
     this.post = post;
     this.tag = tag;
     this.id = new PostTagId(post.getId(), tag.getId());
    }

  }

Using springboot(AuditingEntityListener) to add audit columns. Post and Tag entities are somewhat like -

///////////Tag
    @Data
    @EqualsAndHashCode(callSuper = false, exclude = {"postTags"})
    @ToString( exclude = {"postTags"})
    @Entity
    @Table(name = "tag")
    @EntityListeners(AuditingEntityListener.class)
    public class Tag extends Auditable<String> {
      @Id  
      private Long id;
      
      @Column(name = "tag")
      private String tag;
      
      @OneToMany(mappedBy = "tag", cascade={CascadeType.PERSIST, CascadeType.MERGE, CascadeType.REMOVE})
      private Set<PostTag> postTags;
    }

//////////////POST

    @Data
    @EqualsAndHashCode(callSuper = false, exclude = {"postTags"})
    @ToString( exclude = {"postTags"})
    @Entity
    @Table(name = "post")
    @EntityListeners(AuditingEntityListener.class)
    public class Post extends Auditable<String> {
      @Id  
      private Long id;
      
      @Column(name = "post")
      private String post;
      
      @OneToMany(mappedBy = "post", cascade={CascadeType.PERSIST, CascadeType.MERGE, CascadeType.REMOVE})
      private Set<PostTag> postTags;
    
      public void addTag(Tag tag) {
        PostTag postTag = new PostTag(this, tag);
        if (postTags == null) {
          postTags = new HashSet<>();
        }
        postTags.add(postTag);
        tag.getPostTags().add(postTag);
      }
    }

Code snippet for insertion of tags using addTag() method -

public Post create(Post post) {
    // DefaultTag is some default tag getting from repository   
    post.addTag(DefaultTag)
    return postRepo.save(post);
  }

Insert in post_tag is trying to insert null post_id.

 Hibernate: 
     insert 
     into
         post_tag
         (created_by, created_on, modified_by, modified_on, post_id, tag_id) 
     values
         (?, ?, ?, ?, ?, ?) [0;39m [36mo.h.engine.jdbc.spi.SqlExceptionHelper SQL Error: 0, SQLState:
 23502 [0;39m [36mo.h.engine.jdbc.spi.SqlExceptionHelper  ERROR: null
 value in column "post_id" violates not-null constraint   Detail:
 Failing row contains (null, 100, anonymousUser, anonymousUser,
 2020-07-06 15:22:19.227-06, 2020-07-06 15:22:19.227-06).

Anuja Paradkar Anuja Paradkar · Accepted Answer · 2020-07-08T01:03:30

Removed @EmbededId and used @Id in PostTag class. This way do not need to create embededId in constructor, and hibernate handles id creation. Changes look like this -

@Entity
@Table(name = "post_tag")
@EntityListeners(AuditingEntityListener.class)
@Data
@EqualsAndHashCode(callSuper = false)
public class PostTag extends Auditable<String> implements Serializable {
 
    @ManyToOne
    @Id
    @JoinColumn(name="post_id")
    private Post post;
 
    @ManyToOne
    @Id
    @JoinColumn(name="tag_id")
    private Tag tag;    
  }

Since PostTag(Post, Tag) constructor is removed, addTag(Tag tag) method needs to be refactored in Post entity.

    public void addTag(Tag tag) {
      PostTag postTag = new PostTag();
      postTag.setPost(this);
      postTag.setTag(tag);
      if (postTags == null) {
        postTags = new HashSet<>();
      }
      postTags.add(postTag);
      tag.getPostTags().add(postTag);
   }

Many to Many relation with embedded key is inserting null in primary key

1 Answers