delete element out of array with $pull and $cond operators - mongodb

Question

I want to pull elements out of the array only if some condition is met
This is my document structure:
{
_id: "userId",
posts: [{
_id: "postId",
comments:[{
_id: "commentId",
userid: "some id of an user" // USER
},{
_id: "commentId2",
userid: "some id of an user2"
}]
}]
}
I want to delete the element from the comments array with the given commentId. This should be done only if userid is USER. If that condition isn't met, that means that comment doesn't belongs to the user that wants to delete it so I decline it.
Tried Attempt :
Post.findOneAndUpdate(
{
_id: mongoose.Types.ObjectId(userId)
},
{
$pull: {
$cond: [
{
"posts.$[post].comments.$[comment].userid": {
$eq: USER
}
},
{
$pull: {
comments: {
_id: mongoose.Types.ObjectId(commentId)
}
}
}
]
}
},
{
arrayFilters: [
{
"comment._id": mongoose.Types.ObjectId(commentId)
},
{
"post._id": mongoose.Types.ObjectId(postId)
}
]
}
)
That code above doesn't work, I'm stuck there & I don't know how to continue. maybe somebody knows how to fix this.

Answer 1

You can try below query :
Post.findOneAndUpdate(
{
_id: mongoose.Types.ObjectId(userId) // Fetches actual document
},
// Any matching object that has these fields/values in comments array will be pulled out
{
$pull: {"posts.$[post].comments": { _id : mongoose.Types.ObjectId(commentId), "userid": USER }}},
{
arrayFilters: [
{
"post._id": mongoose.Types.ObjectId(postId) // Checks which object inside `posts` array needs to be updated
}
]
}
)
Note : Use an option { new : true } in mongoose to return updated document, or in shell use { returnNewDocument : true }