How to add conditionally an element in an array in mongodb?

Question

I need to add an element to an array in mongoDB, but only id it doesn't already exist. For now I do as follows:

await db
    .collection(config.MY_COLLECTION)
    .updateOne(
      { _id: ObjectId(userId) },
      { $push: { my_array: ObjectId(idToAdd) } }
    );

In this way I can add the same element x times. How can I avoid it without querying the DB before and do it conditionally server side. I want to do it directly DB side.

Have you checked out $addToSet?

ray
– ray

2021-11-25 21:57:46 +00:00
Commented Nov 25, 2021 at 21:57 — ray
– ray, Commented Nov 25, 2021 at 21:57
Very good @ray! That's the one

Loudrous
– Loudrous

2021-11-25 22:01:39 +00:00
Commented Nov 25, 2021 at 22:01 — Loudrous
– Loudrous, Commented Nov 25, 2021 at 22:01

R2D2 · Accepted Answer · 2021-11-25 22:00:41Z

1

Just replace $push with $addToSet

answered Nov 25, 2021 at 22:00

R2D2

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