Question 207972 in PostgreSQL Question posted in
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Postgresql – Typeorm/Postgres blog like constraint

im creating a blog where you can like a comment or a post with typeorm and postgres, here is the like entitie:

@Entity()
@Unique(["user", "post", "comment"])
export default class Like {
  @PrimaryGeneratedColumn()
  id: number;

  // @Column()
  // likeCount: number;

  @ManyToOne(() => User, (user) => user.likes, { nullable: false })
  user: User;

  @ManyToOne(() => Post, (post) => post.likes)
  post: Post;

  @ManyToOne(() => Comment, (comment) => comment.likes)
  comment: Comment;

I want to create a constraint where a user can like a comment/post only once, in the code above i tried with unique constraints but its not working, how should i do it? should i create two differents tables, one for like-post and one for like-comment? and how do i keep track of how many likes each comment/post have?

i tried unique constraint but is not working

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2

Answers


  1. 0

    Add columns userId, postId, commentId and make a unique index on them.

    Like this^

    @Entity()
@Unique(["userId", "postId", "commentId"])
export default class Like {
  @PrimaryGeneratedColumn()
  id: number;

  // @Column()
  // likeCount: number;

  @Column()
  userId: number;

  @Column()
  postId: number;

  @Column()
  commentId: number;

  @ManyToOne(() => User, (user) => user.likes, { nullable: false })
  user: User;

  @ManyToOne(() => Post, (post) => post.likes)
  post: Post;

  @ManyToOne(() => Comment, (comment) => comment.likes)
  comment: Comment;

    Thus, one User likes only one Comment per Post.

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  2. 0

    you can use a unique constraint on the combination of the user_id and comment_id columns, or the combination of the user_id and post_id columns. this will allow a user to like more than one post/comment. and use foreign keys to link likes with posts/comments to ensure they exist in the database

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