Query objects store complex SQL queries, data aggregation, and filtering methods. ¹

• app/queries

• The Query object should take a relation as it's argument, that should enable the caller to control the scope of the query.
• Query objects should be composable. ²
• Should return an ActiveRecord::Relation. ²

Note: In practice, it's difficult to achieve some of these desired qualities because Caseflow's data spans multiple databases.

Use the Service pattern if you are encapsulating complex logic that requires a read.

• 1: https://github.com/infinum/rails-handbook/blob/master/Design%20Patterns/Query%20Objects.md
• 2: https://medium.flatstack.com/query-object-in-ruby-on-rails-56ea434365f0

Pattern	Description
Service	Alternative for database logic that requires writes