MongoDB 4.2 introduced support for field-level (client-side) encryption: https://docs.mongodb.com/manual/core/security-client-side-encryption/

I propose that this should be supported in the field definitions:

field :name, type: String, encrypted: true
field :phones, type: Array, encrypted: true, encryption_key: xxx

If Mongoid supported this, we would use it heavily at my company. Currently we are using the Mongoid Encrypted Fields gem https://github.com/KoanHealth/mongoid-encrypted-fields