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GHC 9.10.3 · lts/ghc-9.10.x · 248f8f0 · 2026-10-05

Moduleopenapi3-3.2.4Haskell2010

Data.OpenApi.Schema

Types and functions for working with Swagger schema.

  • 1 type
  • 1 class
  • 24 values
  • Packageopenapi3-3.2.4
  • Exports26
  • LanguageHaskell2010
  • LicenceBSD-3-Clause
  • SourceSchema.hs

Encoding

7 declarations
classclass Typeable a => ToSchema a where
#

Convert a type into Schema.

An example type and instance:

{-# LANGUAGE OverloadedStrings #-}   -- allows to write Text literals
{-# LANGUAGE OverloadedLists #-}     -- allows to write Map and HashMap as lists

import Control.Lens
import Data.Proxy
import Data.OpenApi

data Coord = Coord { x :: Double, y :: Double }

instance ToSchema Coord where
  declareNamedSchema _ = do
    doubleSchema <- declareSchemaRef (Proxy :: Proxy Double)
    return $ NamedSchema (Just "Coord") $ mempty
      & type_ ?~ OpenApiObject
      & properties .~
          [ ("x", doubleSchema)
          , ("y", doubleSchema)
          ]
      & required .~ [ "x", "y" ]

Instead of manually writing your ToSchema instance you can use a default generic implementation of declareNamedSchema.

To do that, simply add deriving Generic clause to your datatype and declare a ToSchema instance for your datatype without giving definition for declareNamedSchema.

For instance, the previous example can be simplified into this:

{-# LANGUAGE DeriveGeneric #-}

import GHC.Generics (Generic)

data Coord = Coord { x :: Double, y :: Double } deriving Generic

instance ToSchema Coord

Methods

Instances61ToSchema, …
valuedeclareSchemaRef
  1. :: ToSchema a
  2. => Proxy a
  3. -> Declare (Definitions Schema) (Referenced Schema)
#

Convert a type into a referenced schema if possible and declare all used schema definitions. Only named schemas can be referenced, nameless schemas are inlined.

Schema definitions are typically declared for every referenced schema. If declareSchemaRef returns a reference, a corresponding schema will be declared (regardless of whether it is recusive or not).

valuetoSchema :: ToSchema a => Proxy a -> Schema
#

Convert a type into a schema.

Example1 expression
BSL.putStrLn $ encodePretty $ toSchema (Proxy :: Proxy Int8){    "maximum": 127,    "minimum": -128,    "type": "integer"}
Example1 expression
BSL.putStrLn $ encodePretty $ toSchema (Proxy :: Proxy [Day]){    "items": {        "$ref": "#/components/schemas/Day"    },    "type": "array"}
valuetoSchemaRef :: ToSchema a => Proxy a -> Referenced Schema
#

Convert a type into a referenced schema if possible. Only named schemas can be referenced, nameless schemas are inlined.

Example1 expression
BSL.putStrLn $ encodePretty $ toSchemaRef (Proxy :: Proxy Integer){    "type": "integer"}
Example1 expression
BSL.putStrLn $ encodePretty $ toSchemaRef (Proxy :: Proxy Day){    "$ref": "#/components/schemas/Day"}
valueschemaName :: ToSchema a => Proxy a -> Maybe Text
#

Get type's schema name according to its ToSchema instance.

Example1 expression
schemaName (Proxy :: Proxy Int)Nothing
Example1 expression
schemaName (Proxy :: Proxy UTCTime)Just "UTCTime"
valuetoInlinedSchema :: ToSchema a => Proxy a -> Schema
#

Convert a type into a schema without references.

Example1 expression
BSL.putStrLn $ encodePretty $ toInlinedSchema (Proxy :: Proxy [Day]){    "items": {        "example": "2016-07-22",        "format": "date",        "type": "string"    },    "type": "array"}

WARNING: toInlinedSchema will produce infinite schema when inlining recursive schemas.

Generic schema encoding

4 declarations
valuegenericDeclareNamedSchema
  1. :: (Generic a, GToSchema (Rep a), Typeable a)
  2. => SchemaOptions
  3. -> Proxy a
  4. -> Declare (Definitions Schema) NamedSchema
#

A configurable generic NamedSchema creator. This function applied to defaultSchemaOptions is used as the default for declareNamedSchema when the type is an instance of Generic.

Default implementation will use the name from Typeable instance, including concrete instantioations of type variables.

For example:

Example1 expression
_namedSchemaName $ undeclare $ genericDeclareNamedSchema defaultSchemaOptions (Proxy :: Proxy (Either Int Bool))Just "Either_Int_Bool"

Bounded Integral

Bounded Enum key mappings

valuedeclareSchemaBoundedEnumKeyMapping
  1. :: (Bounded key, Enum key, ToJSONKey key, ToSchema key, ToSchema value)
  2. => Proxy (map key value)
  3. -> Declare (Definitions Schema) Schema
#

Declare Schema for a mapping with Bounded Enum keys. This makes a much more useful schema when there aren't many options for key values.

Example6 expressions
data ButtonState = Neutral | Focus | Active | Hover | Disabled deriving (Show, Bounded, Enum, Generic)instance ToJSON ButtonStateinstance ToSchema ButtonStateinstance ToJSONKey ButtonState where toJSONKey = toJSONKeyText (T.pack . show)type ImageUrl = T.TextBSL.putStrLn $ encodePretty $ toSchemaBoundedEnumKeyMapping (Proxy :: Proxy (Map ButtonState ImageUrl)){    "properties": {        "Active": {            "type": "string"        },        "Disabled": {            "type": "string"        },        "Focus": {            "type": "string"        },        "Hover": {            "type": "string"        },        "Neutral": {            "type": "string"        }    },    "type": "object"}

Note: this is only useful when key is encoded with ToJSONKeyText. If it is encoded with ToJSONKeyValue then a regular schema for [(key, value)] is used.

valuetoSchemaBoundedEnumKeyMapping
  1. :: (Bounded key, Enum key, ToJSONKey key, ToSchema key, ToSchema value)
  2. => Proxy (map key value)
  3. -> Schema
#

A Schema for a mapping with Bounded Enum keys. This makes a much more useful schema when there aren't many options for key values.

Example6 expressions
data ButtonState = Neutral | Focus | Active | Hover | Disabled deriving (Show, Bounded, Enum, Generic)instance ToJSON ButtonStateinstance ToSchema ButtonStateinstance ToJSONKey ButtonState where toJSONKey = toJSONKeyText (T.pack . show)type ImageUrl = T.TextBSL.putStrLn $ encodePretty $ toSchemaBoundedEnumKeyMapping (Proxy :: Proxy (Map ButtonState ImageUrl)){    "properties": {        "Active": {            "type": "string"        },        "Disabled": {            "type": "string"        },        "Focus": {            "type": "string"        },        "Hover": {            "type": "string"        },        "Neutral": {            "type": "string"        }    },    "type": "object"}

Note: this is only useful when key is encoded with ToJSONKeyText. If it is encoded with ToJSONKeyValue then a regular schema for [(key, value)] is used.

Reusing ToParamSchema

Sketching Schemas using ToJSON

2 declarations
valuesketchSchema :: ToJSON a => a -> Schema
#

Make an unrestrictive sketch of a Schema based on a ToJSON instance. Produced schema can be used for further refinement.

Example1 expression
BSL.putStrLn $ encodePretty $ sketchSchema "hello"{    "example": "hello",    "type": "string"}
Example1 expression
BSL.putStrLn $ encodePretty $ sketchSchema (1, 2, 3){    "example": [        1,        2,        3    ],    "items": {        "type": "number"    },    "type": "array"}
Example1 expression
BSL.putStrLn $ encodePretty $ sketchSchema ("Jack", 25){    "example": [        "Jack",        25    ],    "items": [        {            "type": "string"        },        {            "type": "number"        }    ],    "type": "array"}
Example3 expressions
data Person = Person { name :: String, age :: Int } deriving (Generic)instance ToJSON PersonBSL.putStrLn $ encodePretty $ sketchSchema (Person "Jack" 25){    "example": {        "age": 25,        "name": "Jack"    },    "properties": {        "age": {            "type": "number"        },        "name": {            "type": "string"        }    },    "required": [        "age",        "name"    ],    "type": "object"}
valuesketchStrictSchema :: ToJSON a => a -> Schema
#

Make a restrictive sketch of a Schema based on a ToJSON instance. Produced schema uses as much constraints as possible.

Example1 expression
BSL.putStrLn $ encodePretty $ sketchStrictSchema "hello"{    "enum": [        "hello"    ],    "maxLength": 5,    "minLength": 5,    "pattern": "hello",    "type": "string"}
Example1 expression
BSL.putStrLn $ encodePretty $ sketchStrictSchema (1, 2, 3){    "enum": [        [            1,            2,            3        ]    ],    "items": [        {            "enum": [                1            ],            "maximum": 1,            "minimum": 1,            "multipleOf": 1,            "type": "number"        },        {            "enum": [                2            ],            "maximum": 2,            "minimum": 2,            "multipleOf": 2,            "type": "number"        },        {            "enum": [                3            ],            "maximum": 3,            "minimum": 3,            "multipleOf": 3,            "type": "number"        }    ],    "maxItems": 3,    "minItems": 3,    "type": "array",    "uniqueItems": true}
Example1 expression
BSL.putStrLn $ encodePretty $ sketchStrictSchema ("Jack", 25){    "enum": [        [            "Jack",            25        ]    ],    "items": [        {            "enum": [                "Jack"            ],            "maxLength": 4,            "minLength": 4,            "pattern": "Jack",            "type": "string"        },        {            "enum": [                25            ],            "maximum": 25,            "minimum": 25,            "multipleOf": 25,            "type": "number"        }    ],    "maxItems": 2,    "minItems": 2,    "type": "array",    "uniqueItems": true}
Example3 expressions
data Person = Person { name :: String, age :: Int } deriving (Generic)instance ToJSON PersonBSL.putStrLn $ encodePretty $ sketchStrictSchema (Person "Jack" 25){    "enum": [        {            "age": 25,            "name": "Jack"        }    ],    "maxProperties": 2,    "minProperties": 2,    "properties": {        "age": {            "enum": [                25            ],            "maximum": 25,            "minimum": 25,            "multipleOf": 25,            "type": "number"        },        "name": {            "enum": [                "Jack"            ],            "maxLength": 4,            "minLength": 4,            "pattern": "Jack",            "type": "string"        }    },    "required": [        "age",        "name"    ],    "type": "object"}

Inlining Schemas

4 declarations
valueinlineSchemas :: Data s => [Text] -> Definitions Schema -> s -> s
#

Inline any referenced schema if its name is in the given list.

NOTE: if a referenced schema is not found in definitions it stays referenced even if it appears in the list of names.

WARNING: inlineSchemas will produce infinite schemas when inlining recursive schemas.

valueinlineSchemasWhen
  1. :: Data s
  2. => Text -> Bool
  3. -> Definitions Schema
  4. -> s
  5. -> s
#

Inline any referenced schema if its name satisfies given predicate.

NOTE: if a referenced schema is not found in definitions the predicate is ignored and schema stays referenced.

WARNING: inlineSchemasWhen will produce infinite schemas when inlining recursive schemas.

Generic encoding configuration

3 declarations
datadata SchemaOptions
#

Options that specify how to encode your type to Swagger schema.

Constructors