Update
Mongoose 5.7.1 was release and seems to fix the issue, so setting up the useUnifiedTopology
option work as expected.
mongoose.connect(mongoConnectionString, {useNewUrlParser: true, useUnifiedTopology: true});
Original answer
I was facing the same issue and decided to deep dive on Mongoose code: https://github.com/Automattic/mongoose/search?q=useUnifiedTopology&unscoped_q=useUnifiedTopology
Seems to be an option added on version 5.7 of Mongoose and not well documented yet. I could not even find it mentioned in the library history https://github.com/Automattic/mongoose/blob/master/History.md
According to a comment in the code:
- @param {Boolean} [options.useUnifiedTopology=false] False by default. Set to
true
to opt in to the MongoDB driver's replica set and sharded cluster monitoring engine.
There is also an issue on the project GitHub about this error: https://github.com/Automattic/mongoose/issues/8156
In my case I don't use Mongoose in a replica set or sharded cluster and though the option should be false. But if false it complains the setting should be true. Once is true it still don't work, probably because my database does not run on a replica set or sharded cluster.
I've downgraded to 5.6.13 and my project is back working fine. So the only option I see for now is to downgrade it and wait for the fix to update for a newer version.