Question 1

How do I validate optional keys in a map with Schema?

Accepted Answer

Use (s/optional-key :key) in map schemas, as shown in the README with examples like {(s/optional-key :foo) s/Keyword}. This allows keys to be missing without failing validation, and you can combine them with required keys for flexible data shapes.

Question 2

Schema vs clojure.spec: which one should I use?

Accepted Answer

Schema is more lightweight and declarative, focusing on data shapes with rich error messages, while clojure.spec is more powerful for specifications and generative testing. Choose Schema for simplicity and seamless integration with existing Clojure code, especially in teams prioritizing documentation.

Question 3

Can Schema generate random data for testing?

Accepted Answer

Yes, through the experimental schema-generators library, which integrates with clojure.test.check to produce data matching your schemas. This is useful for property-based testing, though it's noted as experimental in the README.

Question 4

How to handle recursive data structures in Schema?

Accepted Answer

Use s/recursive with a var reference, as demonstrated with Tree schemas in the README (e.g., {:value s/Int :children [(s/recursive #'Tree)]}). This allows you to define schemas for nested or infinite data types without manual repetition.

Question 5

Is Schema compatible with ClojureScript projects?

Accepted Answer

Yes, Schema supports both Clojure and ClojureScript, with cross-platform schemas like s/Str and s/Num, and macros that work in both environments. The README includes ClojureScript-specific usage notes, such as :include-macros true.

Question 6

What's the performance impact of enabling Schema validation in production?

Accepted Answer

Validation adds runtime overhead, so it's recommended to use it selectively—perhaps only in development or tests—or optimize with s/validator for repeated checks. The README advises using *assert* flags to control code generation and reduce size.

Prismatic's schema

What is Prismatic's schema?

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