This ends up doing a round-trip to the database server, as it needs to query the `system.indexes` collection. I realize that is the only authoritative way to determine which indexes are in MongoDB, but the ODM might be better served by relying on the indexes defined in ClassMetadata (and we should be clear about that documentation).

In a production deployment, the overhead of this round-trip is undesirable and users should be expected to ensure that the indexes in their metadata are synced with the database (the schema update command does this).