Add and remove from array in single query - node.js

Question

I want to make a query in which i want to know either the user like or unlike my status, now i want to make it on single query so that I will not call the DB 2 times from my NODEJS server, do any have solution of my problem.
For Add We are using
collection.update({ _id: id },
{ $pull: {
'user_id': 'xxxx-xxxx-xxxx-xxxx' }
}
);
For Remove We are using
collection.update({ _id: id },
{ $push: {
'user_id': 'xxxx-xxxx-xxxx-xxxx' }
}
);
Now I want to use both of them in one query like if apply present in fruit array remove it if not add it.

Answer 1

MongoDB does not allow both a $pull and $push or any other operation to update the same "path" ( therefore single array ) in a single statement. This is mainly to do with the logic handling server side where the update operations are never considered to be ordered in a statement.
Example:
{
"responses": [
{ "user": "Tom", "status": "like" },
{ "user": "Sarah", "status": "unlike" }
]
}
Not that it would make much sense, but you cannot do this:
db.collection.update(
{},
{
"$pull": { "responses": { "user": "Tom", "status": "like" },
"$push": { "responses": { "user": "Tom", "status": "unlike" }
}
)
As the single operation here contains both $push and $pull on the "same path" as "responses". Regardless of you you contruct the statement, neither is required to execute in any order at all.
While we could "match" the position for "Tom" and change his "status" to "unlike" instead, a better model is to do this:
{
"likes": ["Tom"],
"unlikes": ["Sarah"],
"likesTotal": 1,
"unlikesTotal": 1,
"totalScore": 0
}
What this means if I want to change the "vote" for "Tom" then you make a construct like this, with the help of Bulk operations to enable a single request and response:
var bulk = db.collection.initializeOrderedBulkOp();
// Cast "Tom's" unlike where they had a "like" already
bulk.find({
"likes": "Tom",
"unlikes": { "$ne": "Tom" }
}).updateOne({
"$pull": { "likes": "Tom" },
"$push": { "unlikes": "Tom" },
"$inc": {
"likesTotal": -1,
"unlikesTotal": 1
}
]);
// Cast "Tom's" new vote where nothing was there at all
bulk.find({
"unlikes": { "$ne": "Tom" },
"likes": { "$ne": "Tom" }
}).updateOne({
"$push": { "unlikes": "Tom" },
"$inc": {
"unlikesTotal": 1,
"totalScore": -1
}
});
bulk.execute();
This produces a really nice pattern. Not only is each update operation here basically "atomic" in that by acting on separate document properties each modifier is allowed to execute without conflict. But also as a "Bulk" operation, the request for "both" update operations that meet all possible conditions here are sent in a single request and received in a single response.
Of course your "client" logic should also be aware of the current status for who has "liked/disliked" on a particular item, but enforcing this in the general API is good practice.
It keeps arrays in check, and also keeps useful counters in check for general data and general querying purposes, without the need to "calculate" lengths of arrays or matching types.