Q:

Get array objects with specific ObjectId in nested array

I'm trying to get a specific array of objects depending on ObjectId they have.
Here is my MongoDB database:
{
    "_id" : ObjectId("59edb571593904117884b721"),
    "userids" : [
            ObjectId("59edb459593904117884b71f")
    ],
    "macaddress" : "MACADDRESS",
    "devices" : [ ],
    "projectorbrand" : "",
}
{
    "_id" : ObjectId("59edb584593904117884b722"),
    "userids" : [
            ObjectId("59edb459593904117884b71f"),
            ObjectId("59e4809159390431d44a9438")
    ],
    "macaddress" : "MACADDRESS2",
    "devices" : [ ],
    "projectorbrand" : "",
}

The command in MongoDB is:
db.getCollection('co4b').find( {
    userids: { $all: [ ObjectId("59edb459593904117884b71f") ] }
} )

This will work and will return an array filtered correctly.
I would like to translate this query in Golang.
Here is my code:
pipe := bson.M{"userids": bson.M{"$all": objectId}}
var objects[]models.Objects
if err := uc.session.DB("API").C("objects").Pipe(pipe).All(&objects); err != nil {
    SendError(w, "error", 500, err.Error())
} else {
    for i := 0; i < len(objects); i++ {
        objects[i].Actions = nil
    }
    uj, _ := json.MarshalIndent(objects, "", " ")
    SendSuccessJson(w, uj)
}

I'm getting error like wrong type for field (pipeline) 3 != 4. I saw that $all needs string array but how to filter by ObjectId instead of string?
Thanks for help

A:

You are attempting to use the aggregation framework in your mgo solution, yet the query you try to implement does not use one (and does not need one).
The query:
db.getCollection('co4b').find({
    userids: {$all: [ObjectId("59edb459593904117884b71f")] }
})

Can simply be transformed to mgo like this:
c := uc.session.DB("API").C("objects")

var objects []models.Objects
err := c.Find(bson.M{"userids": bson.M{
    "$all": []interface{}{bson.ObjectIdHex("59edb459593904117884b71f")},
}}).All(&objects)

Also note that if you're using $all with a single element, you can also implement that query using $elemMatch, which in MongoDB console would like this:
db.getCollection('co4b').find({
    userids: {$elemMatch: {$eq: ObjectId("59edb459593904117884b71f")}}
})

Which looks like this in mgo:
err := c.Find(bson.M{"userids": bson.M{
    "$elemMatch": bson.M{"$eq": bson.ObjectIdHex("59edb459593904117884b71f")},
}}).All(&objects)

