Get last inserted element from mongodb in GoLang using FindOne and $natural

Question

I'm trying to retrieve the last inserted document using FindOne as suggested elsewhere:

collection.FindOne(ctx, bson.M{"$natural": -1})

Get last inserted element from mongodb in GoLang

Here is my example:

    var lastrecord bson.M
if err = collection.FindOne(ctx, bson.M{"$natural": -1}).Decode(&lastrecord); err != nil {
    log.Fatal(err)
}
fmt.Println(lastrecord)

Unfortunately I get the following error:

(BadValue) unknown top level operator: $natural

I'd prefer to use FindOne if possible.

icza · Accepted Answer · 2021-01-13 19:50:58Z

2

You want to sort using natural order, yet you specify it as a filter, which is what the error says.

To use $natural to specify sorting:

opts := options.FindOne().SetSort(bson.M{"$natural": -1})
var lastrecord bson.M
if err = coll.FindOne(ctx, bson.M{}, opts).Decode(&lastrecord); err != nil {
    log.Fatal(err)
}
fmt.Println(lastrecord)

answered Jan 13, 2021 at 19:50

icza

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2 Comments

Ironkaiju Over a year ago

Thanks - I knew there was an additional item I was missing but didn't know how to apply the sort to find one. Are you able to point me at some useful docs on how to construct the opts?

icza Over a year ago

Options is a builder, it has methods to set any option. Check out the docs of course: godoc.org/go.mongodb.org/mongo-driver/mongo/options

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