Leaving this here: note that as per theConnection Strings documentation, the path in the connection string refers to the default authentication database to be used if theauthSource does not define one. While most people consider this to be the default database, I wanted to point out the difference. Not necessarily an issue of this PR as it's already the current behaviour, so feel free to resolve this comment after reading if you think this isn't worth changing.

Sure, that would be better if the optiondatabase had precedence over the database in the path of the URI.

Note thatauthSource should never be assumed to be a database name. For some auth mechanisms it might be set to$external (see:authSource docs).

Does anything enforce that$this->options['id_field'] is actually_id or even a field with a unique index?

I assume this will only ever return one or no documents, but I noticed you uselimit: 1 for the delete operation indoDestroy(), but omit the limit here. I don't disagree with an explicit limit on the delete operation, since the default is to remove all matching documents.

I guess this options were copied fromPdoSessionHandler when this provider was created. This provider has aconfigureSchema orcreateTable methods to init the table. We can add a similar method for MongoDB. But since the collection already have an unique index on_id, I think it's fine to let people that would like to change the id field, initialize the collection themselve.

Note thatauthSource should never be assumed to be a database name. For some auth mechanisms it might be set to$external (see:authSource docs).

Offhand, is there anything in these Symfony adapters that sets driver information like we do for Doctrine ODM and Laravel? If so, should we consider doing so in a subsequent PR? /cc@alcaeus

The connection will mostly come from Doctrine, but I can add user-agent for standalone usage.

I think it makes sense if you're constructing the Manager yourself, but no need to hold up this PR to add that if you want to address it down the line.