Query Object Pattern

Definition
A Query Object is an interpreter, that is, a structure of objects that can form itself into a SQL query (martin fowler).

Applicability

• When there is a need to avoid to know what the database schema looks like to form queries.

Consequences

• Hides the SQL inside parameterized methods.
• Those who write the queries can do so independently of the database schema and changes to the schema can be localized in a single place.

Downsides

• Makes it difficult to form more ad hoc queries.

Sample Code

References

https://www.martinfowler.com/eaaCatalog/queryObject.html

Further Readings
https://github.com/shaynevanasperen/NHibernate.Sessions.Operations
https://lostechies.com/chadmyers/2008/08/02/query-objects-with-the-repository-pattern/
https://crosscuttingconcerns.com/CommandQuery-Object-pattern