Sequelize: Check and add BelongsToMany (N to N) relation

Question

My application got many Users who can like many Posts (N to N). That's why I assigned the following "belongsToMany" Relations for my Models (Sequelize Doc):

// Post Model
models.Post.belongsToMany(models.User, { through: models.PostLikes});

// User Model
models.User.belongsToMany(models.Post, { through: models.PostLikes});

Inside my Post Controller I got the following use case for the "likePost" function:

1. Check if the Post exists. (seems to work)
2. If so, check if the User already liked this Post.

3. If not, assign the N to N relation between User and the Post. (seems to work)

   // User likes Post
   exports.likePost = async (req, res) => {
    const postToLike = await Post.findById(req.body.postId);
    // Check if the Post exists
    if (!postToLike) {
     return res.status(404).json({ error: { message: 'Post not found.' }});
    }
   
    // Did user already like the post?
    // HERE IS THE NOT WORKING PART:
    if (await req.user.hasPost(postToLike).isFulfilled()) {
     return res.status(422).json({ error: { message: 'Already liked post.' }});
    }
   
    // add Like
    await req.user.addPost(postToLike);
    return res.send(postToLike);
   };
   

Now I got the Problem, that I am not able to check if a User already liked a Post. "req.user.hasPost(postToLike).isFulfilled()" always returns false, even if indeed I can see the correct relation in my "PostLikes" DB Table. So how can I correctly:

1. Check if a User already liked a Post.
2. Assign this relation.
3. And remove the relation with Sequelize?

BTW this is how my PostLikes Table looks like:

+----+--------+--------+
| id | userId | postId |
+----+--------+--------+
|  1 |      2 |      3 |
+----+--------+--------+

Answer 1

Looking at the documentation, there is no mention of isFulfilled(). Did you try to do req.user.hasPost(postToLike) ? (Sequelize Doc)