Criteria Pattern in NestJS: Structuring Flexible, Decoupled API Query Contracts

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A developer tutorial on DEV Community demonstrates the Criteria pattern in NestJS using a library book catalogue as a working example. The article shows how a typical query endpoint grows organically, accumulating filter, sort, and pagination parameters directly tied to database field names. This approach creates an implicit, undeclared contract between clients and the database schema, making future changes risky once URLs are shared or scripted externally. The Criteria pattern addresses this by introducing a structured query object that translates client intent into database operations across two explicit boundaries. The result is a more expressive and maintainable API where filters declare their operators and fields are abstracted from underlying collection names.

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