I have a problem with "You may also like" feature in Spring boot JPA - spring-boot

Question

I want to create a simple "You may also like" feature for a blog.
There are posts and each of them has one or more tags. Also a tag can contain many posts. I want to implement the feature where you open a post and the posts, which have similar tags, are recommended to you.
So i created 3 entities:
Post.java
#Entity
#Table
public class Post {
#Id
#Column
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
#Column
private String text;
#Column
private String author;
#OneToMany(mappedBy = "post")
Set<PostTags> postTags;
public Post(){}
public Long getId() {
return id;
}
public void setId(Long id) {
this.id = id;
}
public String getAuthor() {
return author;
}
public void setAuthor(String author) {
this.author = author;
}
public String getText() {
return text;
}
public void setText(String text) {
this.text = text;
}
public Set<PostTags> getPostTags() {
return postTags;
}
public void setPostTags(Set<PostTags> postTags) {
this.postTags = postTags;
}
}
Tags.java
#Entity
#Table
public class Tags {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
#Column
private Long id;
#Column
private String name;
#OneToMany(mappedBy = "tag")
Set<PostTags> postTags;
public Set<PostTags> getPostTags() {
return postTags;
}
public void setPostTags(Set<PostTags> postTags) {
this.postTags = postTags;
}
public Long getId() {
return id;
}
public void setId(Long id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
}
PostTags.java
#Entity
public class PostTags {
#Id
#GeneratedValue (strategy = GenerationType.IDENTITY)
#Column
private Long id;
#ManyToOne
#JoinColumn(name = "post_id")
private Post post;
#ManyToOne
#JoinColumn(name = "tag_id")
private Tags tag;
public PostTags(){}
public Long getId() {
return id;
}
public void setId(Long id) {
this.id = id;
}
public Post getPost() {
return post;
}
public void setPost(Post post) {
this.post = post;
}
public Tags getTag() {
return tag;
}
public void setTag(Tags tag) {
this.tag = tag;
}
}
And repositories:
#Repository
public interface PostTagsRepository extends JpaRepository<PostTags, Long> {
#Query("select p.post from PostTags p where p.tag.id IN :tagIds")
Set<Post> findPostsbyTagIds (List<Long> tagIds);
}
#Repository
public interface PostRepository extends JpaRepository<Post, Long> {
#Query("select p from Post p where p.author = :author")
Set<Post> findPostsByAuthor(String author);
}
I managed to create this feature in an amateurish way, but better than nothing. I piled up everything in one method just to test it:
#GetMapping("/posts")
public Set<Post> showRecommendedPosts(){
//Imitate post id
long postId = 1;
Post postFound = postRepository.findById(postId).get();
Set<PostTags> postTags = postFound.getPostTags();
List<Long> listTagIds = new ArrayList<>();
//extract ids of the tags from the post
for(PostTags tag : postTags){
listTagIds.add(tag.getTag().getId());
}
//find posts by Author
Set<Post> postsByAuthor = postRepository.findPostsByAuthor(postFound.getAuthor());
//find posts by Tags
Set<Post> postsByTagIds = postTagsRepository.findPostsbyTagIds(listTagIds);
//We combine both sets
Set<Post> recommendedPosts = new HashSet<>(postsByAuthor);
recommendedPosts.addAll(postsByTagIds);
recommendedPosts.remove(postFound);
return recommendedPosts;
}
But this works only if i manually add data to "post_tags" table in the db like this:
Here is my question, i don't know how to add multiple tags to a post in Spring. Because it would be something like this:
PostTags newPostTag1 = new PostTags();
newPostTag.setPost(post1);
newPostTag.setTag(tag1);
PostTags newPostTag2 = new PostTags();
newPostTag2.setPost(post1);
newPostTag2.setTag(tag2);
PostTags newPostTag3 = new PostTags();
newPostTag3.setPost(post1);
newPostTag3.setTag(tag3);
And so on...
Therefore, it's not an option. So how can i save tags correctly? Or have my entities been created incorrectly? What is my mistake? Thank you!

Answer 1

I am not sure to understand the idea behind Tag being an Entity.
How I see it is you use the postTags and change it to tags. This tags would be a Set of an enum if you want to restrict the user or a Set of String other way. After that, I would add an endpoint that return post based on a tag or a list of tags for your You may also like feature. This endpoint just make a request to the database (find posts where tags contains givenTag max 10). At the end, you only have one entity :
#Entity
#Table
public class Post {
#Id
#Column
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
#Column
private String text;
#Column
private String author;
#Column
#Convert(converter = StringListConverter.class)
Set<String> tags;
// ...
}
Converter implementation here