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60 lines
2.5 KiB
Markdown
60 lines
2.5 KiB
Markdown
# Clojure.spec Coercion
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The [clojure.spec](https://clojure.org/guides/spec) library specifies the structure of data, validates or destructures it, and can generate data based on the spec.
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## Warning
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`clojure.spec` by itself doesn't support coercion. `reitit` uses [spec-tools](https://github.com/metosin/spec-tools) that adds coercion to spec. Like `clojure.spec`, it's alpha as it leans both on spec walking and `clojure.spec.alpha/conform`, which is concidered a spec internal, that might be changed or removed later.
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## Usage
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For simple specs (core predicates, `spec-tools.core/spec`, `s/and`, `s/or`, `s/coll-of`, `s/keys`, `s/map-of`, `s/nillable` and `s/every`), the transformation is inferred using [spec-walker](https://github.com/metosin/spec-tools#spec-walker) and is automatic. To support all specs (like regex-specs), specs need to be wrapped into [Spec Records](https://github.com/metosin/spec-tools/blob/master/README.md#spec-records).
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There are [CLJ-2116](https://dev.clojure.org/jira/browse/CLJ-2116) and [CLJ-2251](https://dev.clojure.org/jira/browse/CLJ-2251) that would help solve this elegantly. Go vote 'em up.
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## Example
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```clj
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(require '[reitit.coercion.spec])
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(require '[reitit.coercion :as coercion])
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(require '[spec-tools.spec :as spec])
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(require '[clojure.spec.alpha :as s])
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(require '[reitit.core :as r])
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;; simple specs, inferred
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(s/def ::company string?)
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(s/def ::user-id int?)
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(s/def ::path-params (s/keys :req-un [::company ::user-id]))
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(def router
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(r/router
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["/:company/users/:user-id" {:name ::user-view
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:coercion reitit.coercion.spec/coercion
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:parameters {:path ::path-params}}]
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{:compile coercion/compile-request-coercers}))
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(defn match-by-path-and-coerce! [path]
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(if-let [match (r/match-by-path router path)]
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(assoc match :parameters (coercion/coerce! match))))
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```
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Successful coercion:
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```clj
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(match-by-path-and-coerce! "/metosin/users/123")
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; #Match{:template "/:company/users/:user-id",
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; :data {:name :user/user-view,
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; :coercion <<:spec>>
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; :parameters {:path ::path-params}},
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; :result {:path #object[reitit.coercion$request_coercer$]},
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; :path-params {:company "metosin", :user-id "123"},
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; :parameters {:path {:company "metosin", :user-id 123}}
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; :path "/metosin/users/123"}
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```
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Failing coercion:
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```clj
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(match-by-path-and-coerce! "/metosin/users/ikitommi")
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; => ExceptionInfo Request coercion failed...
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```
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