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Plain data Schemas for Clojure/Script.

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Plain data Schemas for Clojure/Script.

STATUS: Pre-alpha, in design and prototyping phase.

Presentations:

Try the online demo. Libraries using malli:

  • Aave, a code checking tool for Clojure.

Examples

Definining and validating Schemas:

(require '[malli.core :as m])

(m/validate int? "1")
; => false

(m/validate int? 1)
; => true

(m/validate [:and int? [:> 6]] 7)
; => true

(def valid?
  (m/validator
    [:map
     [:x boolean?]
     [:y {:optional true} int?]
     [:z string?]]))

(valid? {:x true, :z "kikka"})
; => true

Schemas can have properties:

(def Age
  [:and
   {:title "Age"
    :description "It's an age"
    :json-schema/example 20}
   int? [:> 18]])
   
(m/properties Age)
; => {:title "Age"
;     :description "It's an age"
;     :json-schema/example 20}

Maps are open by default:

(m/validate
  [:map [:x int?]]
  {:x 1, :extra "key"})
; => true

Maps can be closed with :closed property:

(m/validate
  [:map {:closed true} [:x int?]]
  {:x 1, :extra "key"})
; => false

Maps keys are not limited to keywords:

(m/validate
  [:map
   ["status" [:enum "ok"]]
   [1 any?]
   [nil any?]
   [::a string?]
   [[1 2 3] number?]]
  {"status" "ok"
   1 'number
   nil :yay
   ::a "properly awesome"
   [1 2 3] 1})
; => true

String schemas

Using a predicate:

(m/validate string? "kikka")

Using :string Schema:

(m/validate :string "kikka")
; => true

(m/validate [:string {:min 1, :max 4}] "")
; => false

Function schemas

:fn allows any predicat function to be used:

(def my-schema
  [:and
   [:map
    [:x int?]
    [:y int?]]
   [:fn (fn [{:keys [x y]}] (> x y))]])
   
(m/validate my-schema {:x 1, :y 0})
; => true

(m/validate my-schema {:x 1, :y 2})
; => false

Serializable function schemas using sci:

(def my-schema
  [:and
   [:map
    [:x int?]
    [:y int?]]
   [:fn '(fn [{:keys [x y]}] (> x y))]])

(m/validate my-schema {:x 1, :y 0})
; => true

(m/validate my-schema {:x 1, :y 2})
; => false

Error Messages

Detailed errors with m/explain:

(def Address
  [:map
   [:id string?]
   [:tags [:set keyword?]]
   [:address
    [:map
     [:street string?]
     [:city string?]
     [:zip int?]
     [:lonlat [:tuple double? double?]]]]])

(m/explain
  Address
  {:id "Lillan"
   :tags #{:artesan :coffee :hotel}
   :address {:street "Ahlmanintie 29"
             :city "Tampere"
             :zip 33100
             :lonlat [61.4858322, 23.7854658]}})
; => nil

(m/explain
  Address
  {:id "Lillan"
   :tags #{:artesan "coffee" :garden}
   :address {:street "Ahlmanintie 29"
             :zip 33100
             :lonlat [61.4858322, nil]}})
;{:schema [:map
;          [:id string?]
;          [:tags [:set keyword?]]
;          [:address [:map
;                     [:street string?]
;                     [:city string?]
;                     [:zip int?]
;                     [:lonlat [:tuple double? double?]]]]],
; :value {:id "Lillan",
;         :tags #{:artesan :garden "coffee"},
;         :address {:street "Ahlmanintie 29"
;                   :zip 33100
;                   :lonlat [61.4858322 nil]}},
; :errors (#Error{:path [2 1 1], :in [:tags 0], :schema keyword?, :value "coffee"}
;          #Error{:path [3 1],
;                 :in [:address],
;                 :schema [:map
;                          [:street string?]
;                          [:city string?]
;                          [:zip int?]
;                          [:lonlat [:tuple double? double?]]],
;                 :type :malli.core/missing-key,
;                 :malli.core/key :city}
;          #Error{:path [3 1 4 1 2], :in [:address :lonlat 1], :schema double?, :value nil})}

Custom Error Messages

Explain results can be humanized with malli.error/humanize:

(require '[malli.error :as me])

(-> Address
    (m/explain
      {:id "Lillan"
       :tags #{:artesan "coffee" :garden}
       :address {:street "Ahlmanintie 29"
                 :zip 33100
                 :lonlat [61.4858322, nil]}})
    (me/humanize))
;{:tags #{["should be keyword"]}
; :address {:city ["missing required key"]
;           :lonlat [nil ["should be double"]]}}

Error messages can be customized with :error/message and :error/fn properties:

(-> [:map
     [:id int?]
     [:size [:enum {:error/message "should be: S|M|L"} 
             "S" "M" "L"]]
     [:age [:fn {:error/fn '(fn [{:keys [value]} _] (str value ", should be > 18"))}
            '(fn [x] (and (int? x) (> x 18)))]]]
    (m/explain {:size "XL", :age 10})
    (me/humanize
      {:errors (-> me/default-errors
                   (assoc ::m/missing-key {:error/fn (fn [{:keys [in]} _] (str "missing key " (last in)))}))}))
;{:id ["missing key :id"]
; :size ["should be: S|M|L"]
; :age ["10, should be > 18"]}

Messages can be localized:

(-> [:map
     [:id int?]
     [:size [:enum {:error/message {:en "should be: S|M|L"
                                    :fi "pitäisi olla: S|M|L"}}
             "S" "M" "L"]]
     [:age [:fn {:error/fn {:en '(fn [{:keys [value]} _] (str value ", should be > 18"))
                            :fi '(fn [{:keys [value]} _] (str value ", pitäisi olla > 18"))}}
            '(fn [x] (and (int? x) (> x 18)))]]]
    (m/explain {:size "XL", :age 10})
    (me/humanize
      {:locale :fi
       :errors (-> me/default-errors
                   (assoc-in ['int? :error-message :fi] "pitäisi olla numero")
                   (assoc ::m/missing-key {:error/fn {:en '(fn [{:keys [in]} _] (str "missing key " (last in)))
                                                      :fi '(fn [{:keys [in]} _] (str "puuttuu avain " (last in)))}}))}))
;{:id ["puuttuu avain :id"]
; :size ["pitäisi olla: S|M|L"]
; :age ["10, pitäisi olla > 18"]}

Top-level humanized map-errors are under :malli/error:

(-> [:and [:map
           [:password string?]
           [:password2 string?]]
     [:fn {:error/message "passwords don't match"}
      '(fn [{:keys [password password2]}]
         (= password password2))]]
    (m/explain {:password "secret"
                :password2 "faarao"})
    (me/humanize))
; {:malli/error ["passwords don't match"]}

Errors can be targetted using :error/path property:

(-> [:and [:map
           [:password string?]
           [:password2 string?]]
     [:fn {:error/message "passwords don't match"
           :error/path [:password2]}
      '(fn [{:keys [password password2]}]
         (= password password2))]]
    (m/explain {:password "secret"
                :password2 "faarao"})
    (me/humanize))
; {:password2 ["passwords don't match"]}

Spell Checking

For closed schemas, key spelling can be checked with:

(-> [:map [:address [:map [:street string?]]]]
    (mu/closed-schema)
    (m/explain
      {:name "Lie-mi"
       :address {:streetz "Hämeenkatu 14"}})
    (me/with-spell-checking)
    (me/humanize))
;{:address {:street ["missing required key"]
;           :streetz ["should be spelled :street"]}
; :name ["disallowed key"]}

Value Transformation

(require '[malli.transform :as mt])

Two-way schema-driven value transformations with m/decode and m/encode using a m/Transformer.

Default Transformers include: string-transformer, json-transformer, strip-extra-keys-transformer, default-value-transformer and key-transformer.

(m/decode int? "42" mt/string-transformer)
; 42

(m/encode int? 42 mt/string-transformer)
; "42"

Transformations are recursive:

(m/decode
  Address
  {:id "Lillan",
   :tags ["coffee" "artesan" "garden"],
   :address {:street "Ahlmanintie 29"
             :city "Tampere"
             :zip 33100
             :lonlat [61.4858322 23.7854658]}}
  mt/json-transformer)
;{:id "Lillan",
; :tags #{:coffee :artesan :garden},
; :address {:street "Ahlmanintie 29"
;           :city "Tampere"
;           :zip 33100
;           :lonlat [61.4858322 23.7854658]}}

Transform map keys:

(m/decode
  Address
  {:id "Lillan",
   :tags ["coffee" "artesan" "garden"],
   :address {:street "Ahlmanintie 29"
             :city "Tampere"
             :zip 33100
             :lonlat [61.4858322 23.7854658]}}
  (mt/key-transformer {:decode name}))
;{"id" "Lillan",
; "tags" #{:coffee :artesan :garden},
; "address" {"street" "Ahlmanintie 29"
;            "city" "Tampere"
;            "zip" 33100
;            "lonlat" [61.4858322 23.7854658]}}

Transformers can be composed with mt/transformer:

(def strict-json-transformer
  (mt/transformer
    mt/strip-extra-keys-transformer
    mt/json-transformer)

(m/decode
  Address
  {:id "Lillan",
   :EVIL "LYN"
   :tags ["coffee" "artesan" "garden"],
   :address {:street "Ahlmanintie 29"
             :DARK "ORKO"
             :city "Tampere"
             :zip 33100
             :lonlat [61.4858322 23.7854658]}}
  strict-json-transformer)
;{:id "Lillan",
; :tags #{:coffee :artesan :garden},
; :address {:street "Ahlmanintie 29"
;           :city "Tampere"
;           :zip 33100
;           :lonlat [61.4858322 23.7854658]}}

Schema properties can be used to override default transformations:

(m/decode
  [string? {:decode/string 'str/upper-case}]
  "kerran" mt/string-transformer)
; => "KERRAN"

Decoders and encoders as interceptors (with :enter and :leave stages):

(m/decode
  [string? {:decode/string {:enter 'str/upper-case}}]
  "kerran" mt/string-transformer)
; => "KERRAN"
(m/decode
  [string? {:decode/string {:enter '#(str "olipa_" %)
                            :leave '#(str % "_avaruus")}}]
  "kerran" mt/string-transformer)
; => "olipa_kerran_avaruus"

To access Schema (and options) use :compile:

(m/decode
  [int? {:math/multiplier 10
         :decode/math {:compile '(fn [schema _]
                                  (let [multiplier (:math/multiplier (m/properties schema))]
                                    (fn [x] (* x multiplier))))}}]
  12
  (mt/transformer {:name :math}))
; => 120

Going crazy:

(m/decode
  [:map
   {:decode/math {:enter '#(update % :x inc)
                  :leave '#(update % :x (partial * 2))}}
   [:x [int? {:decode/math {:enter '(partial + 2)
                            :leave '(partial * 3)}}]]]
  {:x 1} 
  (mt/transformer {:name :math}))
; => {:x 42}

Default values

Applying default values:

(m/decode [:and {:default 42} int?] nil mt/default-value-transformer)
; => 42

Single sweep of defaults & string encoding:

(m/encode
  [:map {:default {}}
   [:a [int? {:default 1}]]
   [:b [:vector {:default [1 2 3]} int?]]
   [:c [:map {:default {}}
        [:x [int? {:default 42}]]
        [:y int?]]]
   [:d [:map
        [:x [int? {:default 42}]]
        [:y int?]]]
   [:e int?]]
  nil
  (mt/transformer
    mt/default-value-transformer
    mt/string-transformer))
;{:a "1"
; :b ["1" "2" "3"]
; :c {:x "42"}}

Programming with Schemas

(require '[malli.util :as mu])

Updating Schema properties:

(mu/update-properties [:vector int?] assoc :min 1)
; => [:vector {:min 1} int?]

Lifted clojure.core function to work with schemas: select-keys, dissoc, get, assoc, update, get-in, assoc-in, update-in

(mu/get-in Address [:address :lonlat])
; => [:tuple double? double?]

(mu/update-in Address [:address] mu/assoc :country [:enum "fi" "po"])
;[:map
; [:id string?]
; [:tags [:set keyword?]]
; [:address
;  [:map [:street string?]
;   [:city string?]
;   [:zip int?]
;   [:lonlat [:tuple double? double?]]
;   [:country [:enum "fi" "po"]]]]]

(-> Address
    (mu/dissoc :address)
    (mu/update-properties assoc :title "Address"))
;[:map {:title "Address"} 
; [:id string?] 
; [:tags [:set keyword?]]]

Making keys optional or required:

(mu/optional-keys [:map [:x int?] [:y int?]])
;[:map 
; [:x {:optional true} int?] 
; [:y {:optional true} int?]]

(mu/required-keys [:map [:x {:optional true} int?] [:y int?]])
;[:map 
; [:x int?] 
; [:y int?]]

Closing and opening all :map schemas recursively:

(def abcd
  [:map {:title "abcd"}
   [:a int?]
   [:b {:optional true} int?]
   [:c [:map
        [:d int?]]]])

(mu/closed-schema abcd)
;[:map {:title "abcd", :closed true}
; [:a int?]
; [:b {:optional true} int?]
; [:c [:map {:closed true}
;      [:d int?]]]]

(-> abcd 
    mu/closed-schema
    mu/open-schema)
;[:map {:title "abcd"}
; [:a int?]
; [:b {:optional true} int?]
; [:c [:map
;      [:d int?]]]]

Merging Schemas (last value wins):

(mu/merge
  [:map
   [:name string?]
   [:description string?]
   [:address
    [:map
     [:street string?]
     [:country [:enum "finland" "poland"]]]]]
  [:map
   [:description {:optional true} string?]
   [:address
    [:map
     [:country string?]]]])
;[:map
; [:name string?]
; [:description {:optional true} string?]
; [:address [:map
;            [:street string?]
;            [:country string?]]]]

Schema unions (merged values of both schemas are valid for union schema):

(mu/union
  [:map
   [:name string?]
   [:description string?]
   [:address
    [:map
     [:street string?]
     [:country [:enum "finland" "poland"]]]]]
  [:map
   [:description {:optional true} string?]
   [:address
    [:map
     [:country string?]]]])
;[:map
; [:name string?]
; [:description {:optional true} string?]
; [:address [:map
;            [:street string?]
;            [:country [:or [:enum "finland" "poland"] string?]]]]]

Adding generated example values to Schemas:

(m/accept
  [:map
   [:name string?]
   [:description string?]
   [:address
    [:map
     [:street string?]
     [:country [:enum "finland" "poland"]]]]]
  (m/schema-visitor
    (fn [schema]
      (mu/update-properties schema assoc :examples (mg/sample schema {:size 2, :seed 20})))))
;[:map
; {:examples ({:name "", :description "", :address {:street "", :country "poland"}}
;             {:name "W", :description "x", :address {:street "8", :country "finland"}})}
; [:name [string? {:examples ("" "")}]]
; [:description [string? {:examples ("" "")}]]
; [:address
;  [:map
;   {:examples ({:street "", :country "finland"} {:street "W", :country "poland"})}
;   [:street [string? {:examples ("" "")}]]
;   [:country [:enum {:examples ("finland" "poland")} "finland" "poland"]]]]]

Persisting Schemas

Writing and Reading schemas as EDN, no eval needed.

(require '[malli.edn :as edn])

(-> [:and
     [:map
      [:x int?]
      [:y int?]]
     [:fn '(fn [{:keys [x y]}] (> x y))]]
    (edn/write-string)
    (doto prn) ; => "[:and [:map [:x int?] [:y int?]] [:fn (fn [{:keys [x y]}] (> x y))]]"
    (edn/read-string)
    (doto (-> (m/validate {:x 0, :y 1}) prn)) ; => false
    (doto (-> (m/validate {:x 2, :y 1}) prn))) ; => true
;[:and 
; [:map 
;  [:x int?] 
;  [:y int?]] 
; [:fn (fn [{:keys [x y]}] (> x y))]]

Multi Schemas

Closed dispatch with :multi schema and :dispatch property:

(m/validate
  [:multi {:dispatch :type}
   [:sized [:map [:type keyword?] [:size int?]]]
   [:human [:map [:type keyword?] [:name string?] [:address [:map [:country keyword?]]]]]]
  {:type :sized, :size 10})
; true

Any (serializable) function can be used for :dispatch:

(m/validate
  [:multi {:dispatch 'first}
   [:sized [:tuple keyword? [:map [:size int?]]]]
   [:human [:tuple keyword? [:map [:name string?] [:address [:map [:country keyword?]]]]]]]
  [:human {:name "seppo", :address {:country :sweden}}])
; true

:dispatch values should be decoded before actual values:

(m/decode
  [:multi {:dispatch :type
           :decode/string '#(update % :type keyword)}
   [:sized [:map [:type [:= :sized] [:size int?]]]
   [:human [:map [:type [:= :human]] [:name string?] [:address [:map [:country keyword?]]]]]]
  {:type "human"
   :name "Tiina"
   :age "98"
   :address {:country "finland"
             :street "this is an extra key"}}
  (mt/transformer mt/strip-extra-keys-transformer mt/string-transformer))
;{:type :human
; :name "Tiina"
; :address {:country :finland}}

Recursive Schemas

Local Registy allows an easy way to create recursive schemas:

(m/validate
  [:schema {:registry {::cons [:maybe [:tuple pos-int? [:ref ::cons]]]}}
   ::cons]
  [16 [64 [26 [1 [13 nil]]]]])
; => true

Mutual recursion works too:

(m/validate
  [:schema {:registry {::ping [:maybe [:tuple [:= "ping"] [:ref ::pong]]]
                       ::pong [:maybe [:tuple [:= "pong"] [:ref ::ping]]]}}
   ::ping]
  ["ping" ["pong" ["ping" ["pong" ["ping" nil]]]]])
; => true

Nested registries, last definition wins:

(m/validate
  [:schema {:registry {::ping [:maybe [:tuple [:= "ping"] [:ref ::pong]]]
                       ::pong any?}} ;; effectively unreachable
   [:schema {:registry {::pong [:maybe [:tuple [:= "pong"] [:ref ::ping]]]}}
    ::ping]]
  ["ping" ["pong" ["ping" ["pong" ["ping" nil]]]]])
; => true

Value Generation

Schemas can be used to generate values:

(require '[malli.generator :as mg])

;; random
(mg/generate keyword?)
; => :?

;; using seed
(mg/generate [:enum "a" "b" "c"] {:seed 42})
;; => "a"

;; using seed and size
(mg/generate pos-int? {:seed 10, :size 100})
;; => 55740

;; regexs work too
(mg/generate 
  [:re #"^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,63}$"] 
  {:seed 42, :size 10})
; => "CaR@MavCk70OHiX.yZ"

;; gen/elements (note, are not validated)
(mg/generate
  [:and {:gen/elements ["kikka" "kukka" "kakka"]} string?]
  {:seed 10})
; => "kikka"

;; portable gen/fmap
(mg/generate
  [:and {:gen/fmap '(partial str "kikka_")} string?]
  {:seed 10, :size 10})
;; => "kikka_WT3K0yax2"

(require '[clojure.test.check.generators :as gen])

;; gen/gen (note, not serializable)
(mg/generate
  [:sequential {:gen/gen (gen/list gen/neg-int)} int?]
  {:size 42, :seed 42})
; => (-37 -13 -13 -24 -20 -11 -34 -40 -22 0 -10)

Generated values are valid:

(mg/generate Address {:seed 123, :size 4})
;{:id "H7",
; :tags #{:v?.w.t6!.QJYk-/-?s*4
;         :_7U
;         :QdG/Xi8J
;         :*Q-.p*8*/n-J9u}
; :address {:street "V9s"
;           :city ""
;           :zip 3
;           :lonlat [-2.75 -0.625]}}

(m/validate Address (mg/generate Address))
; => true

Sampling values:

;; sampling
(mg/sample [:and int? [:> 10] [:< 100]] {:seed 123})
; => (25 39 51 13 53 43 57 15 26 27)

Inferring Schemas

Inspired by F# Type providers:

(require '[malli.provider :as mp])

(def samples
  [{:id "Lillan"
    :tags #{:artesan :coffee :hotel}
    :address {:street "Ahlmanintie 29"
              :city "Tampere"
              :zip 33100
              :lonlat [61.4858322, 23.7854658]}}
   {:id "Huber",
    :description "Beefy place"
    :tags #{:beef :wine :beer}
    :address {:street "Aleksis Kiven katu 13"
              :city "Tampere"
              :zip 33200
              :lonlat [61.4963599 23.7604916]}}])

(mp/provide samples)
;[:map
; [:id string?]
; [:tags [:set keyword?]]
; [:address
;  [:map
;   [:street string?]
;   [:city string?]
;   [:zip number?]
;   [:lonlat [:vector double?]]]]
; [:description {:optional true} string?]]

All samples are valid against the inferred schema:

(every? (partial m/validate (mp/provide samples)) samples)
; => true

Map-syntax

Schemas can converted into map-syntax (with keys :type and optionally :properties and :children):

(def Schema
  [:map
   [:id string?]
   [:tags [:set keyword?]]
   [:address
    [:map
     [:street string?]
     [:lonlat [:tuple double? double?]]]]])

(m/to-map-syntax Schema)
;{:type :map,
; :children [[:id nil {:type string?}]
;            [:tags nil {:type :set
;                        :children [{:type keyword?}]}]
;            [:address nil {:type :map,
;                           :children [[:street nil {:type string?}]
;                                      [:lonlat nil {:type :tuple
;                                                    :children [{:type double?} {:type double?}]}]]}]]}

... and back:

(-> Schema (m/to-map-syntax) (m/from-map-syntax) (mu/equals Schema))
; => true

Schema Transformation

Schemas can be transformed using the Visitor Pattern.

The identity visitor:

(m/accept 
  Address 
  (m/schema-visitor identity))
;[:map
; [:id string?]
; [:tags [:set keyword?]]
; [:address
;  [:map
;   [:street string?]
;   [:city string?]
;   [:zip int?]
;   [:lonlat [:tuple double? double?]]]]]

Adding :title property to schemas:

(m/accept
  Address
  (m/schema-visitor #(mu/update-properties % assoc :title (name (m/type %)))))
;[:map {:title "map"}
; [:id [string? {:title "string?"}]]
; [:tags [:set {:title "set"} [keyword? {:title "keyword?"}]]]
; [:address
;  [:map {:title "map"}
;   [:street [string? {:title "string?"}]]
;   [:city [string? {:title "string?"}]]
;   [:zip [int? {:title "int?"}]]
;   [:lonlat [:tuple {:title "tuple"} [double? {:title "double?"}] [double? {:title "double?"}]]]]]]

Adding :path property to schemas:

(m/accept
  Address
  (fn [schema children in options]
    (m/into-schema
      (m/type schema)
      (cond-> (m/properties schema) (seq in) (assoc :path in))
      children options)))
;[:map [:id [string? {:path [:id]}]]
; [:tags [:set {:path [:tags]}
;         [keyword? {:path [:tags :malli.core/in]}]]]
; [:address
;  [:map {:path [:address]}
;   [:street [string? {:path [:address :street]}]]
;   [:city [string? {:path [:address :city]}]]
;   [:zip [int? {:path [:address :zip]}]]
;   [:lonlat
;    [:tuple {:path [:address :lonlat]}
;     [double? {:path [:address :lonlat 0]}]
;     [double? {:path [:address :lonlat 1]}]]]]]]

Transforming schemas into nested maps:

(m/accept
  Address
  (fn [schema children _ _]
    (-> (m/properties schema)
        (assoc :malli/type (m/type schema))
        (cond-> (seq children) (assoc :malli/children children)))))
;{:malli/type :map,
; :malli/children [[:id nil {:malli/type string?}]
;                  [:tags nil {:malli/type :set
;                              :malli/children [{:malli/type keyword?}]}]
;                  [:address nil {:malli/type :map,
;                                 :malli/children [[:street nil {:malli/type string?}]
;                                                  [:city nil {:malli/type string?}]
;                                                  [:zip nil {:malli/type int?}]
;                                                  [:lonlat nil {:malli/type :tuple
;                                                                :malli/children [{:malli/type double?}
;                                                                                 {:malli/type double?}]}]]}]]}

JSON Schema

Transforming Schemas into JSON Schema:

(require '[malli.json-schema :as json-schema])

(json-schema/transform Address)
;{:type "object",
; :properties {:id {:type "string"},
;              :tags {:type "array"
;                     :items {:type "string"}
;                     :uniqueItems true},
;              :address {:type "object",
;                        :properties {:street {:type "string"},
;                                     :city {:type "string"},
;                                     :zip {:type "integer", :format "int64"},
;                                     :lonlat {:type "array",
;                                              :items [{:type "number"} {:type "number"}],
;                                              :additionalItems false}},
;                        :required [:street :city :zip :lonlat]}},
; :required [:id :tags :address]}

Custom transformation via :json-schema namespaced properties:

(json-schema/transform
  [:enum
   {:title "Fish"
    :description "It's a fish"
    :json-schema/type "string"
    :json-schema/default "perch"}
   "perch" "pike"])
;{:title "Fish"
; :description "It's a fish"
; :type "string"
; :default "perch"
; :enum ["perch" "pike"]}

Full override with :json-schema property:

(json-schema/transform 
  [:map {:json-schema {:type "file"}} 
   [:file any?]])
; {:type "file"}

Swagger2

Transforming Schemas into Swagger2 Schema:

(require '[malli.swagger :as swagger])

(swagger/transform Address)
;{:type "object",
; :properties {:id {:type "string"},
;              :tags {:type "array"
;                     :items {:type "string"}
;                     :uniqueItems true},
;              :address {:type "object",
;                        :properties {:street {:type "string"},
;                                     :city {:type "string"},
;                                     :zip {:type "integer", :format "int64"},
;                                     :lonlat {:type "array",
;                                              :items {},
;                                              :x-items [{:type "number", :format "double"}
;                                                        {:type "number", :format "double"}]}},
;                        :required [:street :city :zip :lonlat]}},
; :required [:id :tags :address]}

Custom transformation via :swagger and :json-schema namespaced properties:

(swagger/transform
  [:enum
   {:title "Fish"
    :description "It's a fish"
    :swagger/type "string"
    :json-schema/default "perch"}
   "perch" "pike"])
;{:title "Fish"
; :description "It's a fish"
; :type "string"
; :default "perch"
; :enum ["perch" "pike"]}

Full override with :swagger property:

(swagger/transform 
  [:map {:swagger {:type "file"}} 
   [:file any?]])
; {:type "file"}

Performance

Validation:

(require '[clojure.spec.alpha :as s])
(require '[criterium.core :as cc])

;; 40ns
(let [spec (s/and int? (s/or :pos-int pos-int? :neg-int neg-int?))
      valid? (partial s/valid? spec)]
  (cc/quick-bench
    (valid? spec 0)))

;; 5ns
(let [valid? (m/validator [:and int? [:or pos-int? neg-int?]])]
  (cc/quick-bench
    (valid? 0)))

Coercion:

(require '[spec-tools.core :as st])

(s/def ::id int?)
(s/def ::name string?)

;; 14µs
(let [spec (s/keys :req-un [::id ::name])
      transform #(st/coerce spec % st/string-transformer)]
  (cc/quick-bench
    (transform {:id "1", :name "kikka"})))

;; 140ns
(let [schema [:map [:id int?] [:name string?]]
      transform (m/decoder schema transform/string-transformer)]
  (cc/quick-bench
    (transform {:id "1", :name "kikka"})))

Schema Registry

Schemas are looked up using a malli.registry/Registry protocol, which is effectively a map from schema type to a schema recipe (schema ast, Schema or IntoSchema instance).

Custom Registry can be passed in to all/most malli public apis via the optional options map using :registry key. If omitted, malli.core/default-registry is used.

;; the default registry
(m/validate [:maybe string?] "kikka")
; => true

;; registry as explicit options
(m/validate [:maybe string?] "kikka" {:registry m/default-registry})
; => true

The default immutable registry is merged from the following parts, enabling easy re-composition of custom schema sets:

malli.core/predicate-schemas

Contains both function values and unqualified symbol representations for all relevant core predicates. Having both representations enables reading forms from both code (function values) and EDN-files (symbols): any?, some?, number?, integer?, int?, pos-int?, neg-int?, nat-int?, float?, double?, boolean?, string?, ident?, simple-ident?, qualified-ident?, keyword?, simple-keyword?, qualified-keyword?, symbol?, simple-symbol?, qualified-symbol?, uuid?, uri?, decimal?, inst?, seqable?, indexed?, map?, vector?, list?, seq?, char?, set?, nil?, false?, true?, zero?, rational?, coll?, empty?, associative?, sequential?, ratio? and bytes?.

malli.core/class-schemas

Class-based schemas, contains java.util.regex.Pattern & js/RegExp.

malli.core/comparator-schemas

Comparator functions as keywords: :>, :>=, :<, :<=, := and :not=.

malli.core/base-schemas

Contains :and, :or, :map, :map-of, :vector, :list, :sequential, :set, :tuple, :enum, :maybe, :multi, :re and :fn.

Custom registry

Example to create a custom registry without the default core predicates and with :bool and :int Schemas:

(def registry
  (merge
    (m/class-schemas)
    (m/comparator-schemas)
    (m/base-schemas)
    {:int (m/fn-schema :int int?)
     :bool (m/fn-schema :bool boolean?)}))

(m/validate [:or :int :bool] 'kikka {:registry registry})
; => false

(m/validate [:or :int :bool] 123 {:registry registry})
; => true

Predicate Schemas don't work anymore:

(m/validate int? 123 {:registry registry})
; Syntax error (ExceptionInfo) compiling
; :malli.core/invalid-schema

Local registry

Any schema can define a local registry using :registry schema property:

(def Adult
  [:map {:registry {::age [:and int? [:> 18]]}}
   [:age ::age]])

(mg/generate Adult {:size 10, :seed 1})
; => {:age 92}

Local registries can be persisted:

(-> Adult
    (malli.edn/write-string)
    (malli.edn/read-string)
    (m/validate {:age 46}))
; => true

See also Recursive Schemas.

Changing the default registry

Using custom registries via :registry option is a simple solution, but this needs to be done for all public api calls. Also, with ClojureScript, the large (100+ schemas) default registry is not subject to any Dead Code Elimination (DCE), even if the schemas are not used in the application.

Malli allows the default registry to be replaced, with the following compiler/jvm bootstrap:

  • cljs: :closure-defines {malli.registry/type "custom"}
  • clj: :jvm-opts ["-Dmalli.registry/type=custom"]

It changes the default registry to empty one, which can be changed using malli.registry/set-default-registy!. Empty default registry enableds DCE for all unsed schema implementations.

Malli supports multiple types of registries.

Immutable registry

(require '[malli.registry :as mr])

;; - cljs: :closure-defines {malli.registry/type "custom"}
;; -  clj: :jvm-opts ["-Dmalli.registry/type=custom"]
(mr/set-default-registry!
  {:string (m/-string-schema)
   :maybe (m/-maybe-schema)
   :map (m/-map-schema)})

(m/validate
  [:map [:maybe [:maybe :string]]]
  {:maybe "sheep"})
; => true

;; gzipped malli.core size as js down from 12Kb -> 1.2Kb

Mutable registry

clojure.spec introduces a mutable global registry for specs. The mutable registry in malli forced you to bring in your own state atom and functions how to work with it:

Using a custom registry atom:

(def registry*
  (atom {:string (m/-string-schema)
         :maybe (m/-maybe-schema)
         :map (m/-map-schema)}))

(defn register! [type ?schema]
  (swap! registry* assoc type ?schema))

;; - cljs: :closure-defines {malli.registry/type "custom"}
;; -  clj: :jvm-opts ["-Dmalli.registry/type=custom"]
(mr/set-default-registry!
  (mr/mutable-registry registry*))

(register! :non-empty-string [:string {:min 1}])

(m/validate :non-empty-string "malli")
; => true

The mutable registry can also passed in as explicit option:

(def registry (mr/mutable-registry registry*))

(m/validate :non-empty-string "malli" {:registry registry})
; => true

Dynamic Registry

If you know what you are doing, you can also use dynamic scope to pass in default schema registry:

;; - cljs: :closure-defines {malli.registry/type "custom"}
;; -  clj: :jvm-opts ["-Dmalli.registry/type=custom"]
(mr/set-default-registry!
  (mr/dynamic-registry))

(binding [mr/*registry* {:string (m/-string-schema)
                         :maybe (m/-maybe-schema)
                         :map (m/-map-schema)
                         :non-empty-string [:string {:min 1}]}]
  (m/validate :non-empty-string "malli"))
; => true

Composite Registry

Registries can be composed:

(require '[malli.core :as m])
(require '[malli.registry :as mr])

;; bring your own evil
(def registry (atom {}))

(defn register! [type schema]
  (swap! registry assoc type schema))

;; - cljs: :closure-defines {malli.registry/type "custom"}
;; -  clj: :jvm-opts ["-Dmalli.registry/type=custom"]
(mr/set-default-registry!
  ;; linear search
  (mr/composite-registry
    ;; immutable registry
    {:map (m/-map-schema)}
    ;; mutable (spec-like) registry
    (mr/mutable-registry registry)
    ;; on the perils of dynamic scope
    (mr/dynamic-registry)))

;; mutate like a boss
(register! :maybe (m/-maybe-schema))

;; ☆.。.:*・°☆.。.:*・°☆.。.:*・°☆.。.:*・°☆
(binding [mr/*registry* {:string (m/-string-schema)}]
  (m/validate
    [:map [:maybe [:maybe :string]]]
    {:maybe "sheep"}))
; => true

Entities and Values

Schemas as just data, so they can be either inlined (values) or referenced (entities) in other schemas. For validation, they work the same way, but for model documentation, they are kept as separate.

Value Schemas

Schemas can be represented as abstract schema syntax and referenced as values:

(def Age
  [:and int? [:> 18]])

(def User
  [:map
   [:name string?]
   [:age Age]])

(m/validate 
  User 
  {:name "Mirjami", :age 62})
; => true

NOTE: Schema format validation only occurs when a m/schema is called, so here Age and User could contain syntax errors.

Entity Schemas

Wrapping schemas into m/schema makes them first class entities. Here User is an entity, while Age is a (embedded) value.

(def Age
  [:and int? [:> 18]])

(def User
  (m/schema
    [:map
     [:name string?]
     [:age Age]]))

(m/validate 
  User 
  {:name "Mirjami", :age 62})
; => true

Motivation

We are building dynamic multi-tenant systems where data-models should be first-class: they should drive the runtime value transformations, forms and processes. We should be able to edit the models at runtime, persist them and load them back from database and over the wire, for both Clojure and ClojureScript. Think of JSON Schema, but for Clojure/Script.

Hasn't the problem been solved (many times) already?

There is Schema, which is awesome, proven and collaborative open source project, and we absolutely love it. We still use it in most of our projects. Sad part: serializing & de-serializing schemas is non-trivial and there is no back-tracking on branching.

Spec is the de facto data specification library for Clojure. It has many great ideas, but it is based on macros, it has a global registry and it doesn't support runtime transformations. Spec-tools was created to "fix" some of the things, but after three years of developing it, it's still kinda hack and not fun to maintain.

So, we decided to spin out our own library, which would do all the things we feel is important for dynamic system development. It's based on the best parts of the existing libraries and several project-specific tools we have done over the years.

If you have expectations (of others) that aren't being met, those expectations are your own responsibility. You are responsible for your own needs. If you want things, make them.

Links (and thanks)

Running tests

We use Kaocha as a test runner. Before running the tests, you need to install NPM dependencies.

npm install
bin/kaocha

Installing locally

clj -Ajar
clj -Ainstall

Bundle size for cljs

npx shadow-cljs run shadow.cljs.build-report app /tmp/report.html

Checking the generated code

npx shadow-cljs release app --pseudo-names

License

Copyright © 2019-2020 Metosin Oy and contributors.

Available under the terms of the Eclipse Public License 2.0, see LICENSE.

About

Plain data Schemas for Clojure/Script.

License:Eclipse Public License 2.0

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