dcj / malli

Plain data Schemas for Clojure/Script.

malli

Plain data Schemas for Clojure/Script.

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

• Schemas as plain data
• Schema-driven Validation
• Schema-driven Value Transformation
• Schema-driven Value Generation
• Inferring Schemas from sample values
• Tools for programming with Schemas
• First class error-messages including spell checking
• Schema Transformations to JSON Schema and Swagger2
• Multi-schemas, default values and persisting schemas
• No global state, explicit everything
• Fast

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

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}}

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})
; => "[e-mail]"

;; 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

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?]]]]]

Transforming schemas into map-syntax:

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

Registry

All public functions take optional options map with optional :registry key. It is an map of name->IntoSchema. It defaults to malli.core/default-registry which is an merge of the following subregistries:

malli.core/predicate-registry

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-registry

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

malli.core/comparator-registry

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

malli.core/base-registry

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 :string and :int Schemas:

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

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

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

Predicate Schemas don't work anymore:

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

Mutable registry

clojure.spec introduces a mutable global registry for specs. There is no such thing in malli, but you can create it yourself.

Using a custom registry atom:

(defonce my-registry
  (atom m/default-registry))

(defn register! [k schema]
  (swap! my-registry assoc k (m/schema schema {:registry @my-registry))
  k)

(register! ::id int?)
;; => :user/id

(register! ::name string?)
;; => :user/name   

(register! ::new-user [:tuple ::id ::name])
;; => :user/new-user

(m/validate 
  [:tuple ::id ::name] 
  [18 "and life"] 
  {:registry @my-registry})
;; => true   

; - OR -   

(m/validate 
  ::new-user
  [18 "and life"] 
  {:registry @my-registry})
;; => true

Mutating the default registry (not recommended):

(defn evil-register! [k ?schema]
  (alter-var-root
    #'m/default-registry
    (constantly
      (assoc m/default-registry k (m/schema ?schema))))
  k)

(evil-register! ::int int?)
; :user/int

(m/validate ::int 1)
; => 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.

• Rich Hickey, Open Source is Not About You

Links (and thanks)

• Schema https://github.com/plumatic/schema
• Clojure.spec https://clojure.org/guides/spec
• Spell-spec https://github.com/bhauman/spell-spec
• JSON Schema https://json-schema.org/understanding-json-schema/index.html
• Spec-provider: https://github.com/stathissideris/spec-provider
• F# Type Providers: https://docs.microsoft.com/en-us/dotnet/fsharp/tutorials/type-providers/
• Core.typed https://github.com/clojure/core.typed
• TypeScript https://www.typescriptlang.org/
• Struct https://funcool.github.io/struct/latest/
• JOI https://github.com/hapijs/joi

Running tests

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

npm install
bin/kaocha

License

Copyright © 2018-2020 Metosin Oy and contributors.

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