How to push object to an existing array in MongoDB

Question

I'm trying to figure out how to push a new object to an array in Go.

Screenshot of my DB:

I need to push a new object under actors array (where maximum size is 20 items in this array).

In Node.js I would have run { $push: { "actors": {$sort: {_id: 1}, $each: [{"name": "test"}], $slice: -20}} }

But in Go I'm not sure what is the correct syntax for it.

This is how my collection struct is defined:

type General struct {
    ID              primitive.ObjectID  `bson:"_id"`
    general         string              `bson:"general,omitempty"`
    Actors []struct{
        ID          primitive.ObjectID  `bson:"_id"`
        name        string              `bson:"name,omitempty"`
    }
}

**** EDIT ****

Regrading the generation of an ObjectId:

I've updated my code according to your answer:

update := bson.D{{"$push", bson.D{{"actors", bson.D{{"$sort", bson.D{{"_id", 1}}}, {"$each", bson.A{bson.D{{"name", "test"}, {"_id", primitive.NewObjectId()}}}}, {"$slice", -20}}}}}}

But when I run the code then I get the following error: undefined: primitive.NewObjectId (exit status 2)

If I just run fmt.Println(primitive.NewObjectID()) then I can see a new ObjectId is printed... so i'm trying to figure out why it is not working in the update query.

(I've imported "go.mongodb.org/mongo-driver/bson/primitive")

Oluwafemi Sule · Accepted Answer · 2023-01-18 11:01:02Z

2

You can build the update document or pipeline using the bson primitives in "go.mongodb.org/mongo-driver/bson" package.

Generate a ObjectId with the NewObjectID function in the primitive package.

import (
    "fmt"
    "context"
    "go.mongodb.org/mongo-driver/bson/primitive"
)
//...

update := bson.D{{"$push", bson.D{{"actors", bson.D{{"$sort", bson.D{{"_id", 1}}}, {"$each", bson.A{bson.D{{"name", "test"}, {"_id", primitive.NewObjectID()}}}}, {"$slice", -20}}}}}}

Then run the update pipeline against your collection.

import (
    "fmt"
    "context"
    "go.mongodb.org/mongo-driver/bson"
)

//...
filter := bson.D{{"_id", 12333}}
result, err := collection.UpdateOne(context.Background(), filter, update)

edited Jan 18, 2023 at 11:01

answered Jan 17, 2023 at 12:31

Oluwafemi Sule

39.3k1 gold badge63 silver badges88 bronze badges

Sign up to request clarification or add additional context in comments.

4 Comments

Yoni Mayer Over a year ago

Great that's seems to work well! One more question, how do I create _id on default when inserting a new actor? thx again

Oluwafemi Sule Over a year ago

@YoniMayer Glad it worked out fine. I have updated my answer to include how to generate a new ObjectId for the actor.

Yoni Mayer Over a year ago

Thanks for your response. something is still not working correctly for me, and I get an error - I've updated my original question (please see EDIT part)

Oluwafemi Sule Over a year ago

I had a typo in the function name. The function should be NewObjectID not NewObjectId

Collectives™ on Stack Overflow

How to push object to an existing array in MongoDB

1 Answer 1

4 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

4 Comments

Your Answer

Sign up or log in

Post as a guest

Related