sequelize count associated table rows - mysql

Question

Using sequelize and mySQL, I have two tables: User and Post.
Relation between two tables is M : N
db.User.belongsToMany(db.Post, { through: "Likes", as: "Liked" });
db.Post.belongsToMany(db.User, { through: "Likes", as: "Likers" });
What I want is getting post with whole likers id and count of whole likers.
I know how to get whole likers like this.
const post = await Post.findOne({
where: { id: postId },
attributes: ["id", "title", "imageUrl"],
include: [{
model: User,
as: "Likers",
attributes: ["id"],
through: { attributes: [] },
}]
})
// result
{
"id": 36,
"title": "test",
"imageUrl": "하늘이_1644886996449.jpg",
"Likers": [
{
"id": 13
},
{
"id": 16
}
]
}
And, I also know how to get count of whole likers.
const post = await Post.findOne({
where: { id: postId },
attributes: ["id", "title", "imageUrl"],
include: [{
model: User,
as: "Likers",
attributes: [[sequelize.fn("COUNT", "id"), "likersCount"]],
}]
})
// result
{
"id": 36,
"title": "test",
"imageUrl": "하늘이_1644886996449.jpg",
"Likers": [
{
"likersCount": 2
}
]
}
But, I don't know how to get both of them at once.
Check the result when I use both of them.
{
model: User,
as: "Likers",
attributes: ["id", [sequelize.fn("COUNT", "id"), "likersCount"]],
through: { attributes: [] },
}
// result
"Likers": [
{
"id": 13,
"likersCount": 2
}
]
It only shows 1 liker(id: 13)
It must show another liker(id: 16).
What is the problem?

Answer 1

It shows only one because COUNT is an aggregating function and it groups records to count them. So the only way to get both - use a subquery to count records in a junction table while getting records on the other end of M:N relationship.
const post = await Post.findOne({
where: { id: postId },
attributes: ["id", "title", "imageUrl",
// you probably need to correct the table and fields names
[Sequelize.literal('(SELECT COUNT(*) FROM Likes where Likes.postId=Post.id)'), 'LikeCount']],
include: [{
model: User,
as: "Likers",
attributes: ["id"],
through: { attributes: [] },
}]
})