Are field level uniqueness constraints still supported in Mongo(ose)?
Yes, unique indexes are still supported in Mongoose; see here and here in the current docs.
Examples from the linked docs:
var s = new Schema({ date: { type: Date, index: { unique: true, expires: '1d' }});var s = new Schema({ name: { type: String, unique: true }});Schema.path('my.path').index({ unique: true, sparse: true });Schema.path('name').index({ unique: true });