MongoDB update operation not working using golang mongo-driver

Question

This is with reference to

How to remove a document inside an array in mongodb using $pull

I need to remove empty sub arrays. I need to code this query in go lang

db.getCollection('workflows').update({<find condition>}, {$pull: {"workflows":[]  } }   )

So I've written the below code

nquery := bson.D {
    {"level", "application"},
    {"workflowName", workflowName},
    {"applicationName", applicationName},
}
nupdate := bson.M{"$pull": bson.M{"workflows":"[]"}}
UpdateOne(getContext(), nquery, nupdate)

The result of UpdateOne shows my query has matched but hasn't modified anything. So I'm guessing there is some problem with the nupdate. What am I doing wrong ?

The UpdateOne function is part of the mongo-driver for go lang

icza · Accepted Answer · 2021-01-17 13:31:04Z

2

"[]" is not an empty array in the query, it's a string having an opening and closing square brackets.

The MongoDB empty array can be "modeled" with an empty slice in Go, e.g. with a value of type []interface{}, so a composite literal of this type is []interface{}{}.

So use this:

nupdate := bson.M{"$pull": bson.M{"workflows": []interface{}{}}}

edited Jan 17, 2021 at 13:31

answered Jan 17, 2021 at 13:04

icza

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R2D2 · Accepted Answer · 2021-01-17 13:19:47Z

1

The square brackets "[]" shall not be in quotes since now they are interpreted as string ... , they need to be added just as square brackets [] and require in golang: &[]int{} to be translated by the mongo goland driver to empty array ...

edited Jan 17, 2021 at 13:19

answered Jan 17, 2021 at 12:41

R2D2

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2 Comments

Abbas Over a year ago

Tried nupdate := bson.M{"$pull": bson.M{"workflows":[] } } , it says syntax error: unexpected }, expecting type go. Sorry I'm new to go, so is this correct ?

Abbas Over a year ago

nupdate := bson.M{"$pull": bson.M{"workflows": &[]int{} } } this worked ! Thanks

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