Morpheus GraphQL
Build GraphQL APIs with your favourite functional language!
Morpheus GraphQL (Server & Client) helps you to build GraphQL APIs in Haskell with native haskell types.
Morpheus will convert your haskell types to a GraphQL schema and all your resolvers are just native Haskell functions. Mopheus GraphQL can also convert your GraphQL Schema or Query to Haskell types and validate them in compile time.
Morpheus is still in an early stage of development, so any feedback is more than welcome, and we appreciate any contribution!
Just open an issue here on GitHub, or join our Slack channel to get in touch.
Getting Started
Setup
To get started with Morpheus, you first need to add it to your project's dependencies, as follows (assuming you're using hpack):
package.yml
dependencies:
- morpheus-graphql
Additionally, you should tell stack which version to pick:
stack.yml
resolver: lts-14.8
extra-deps:
- morpheus-graphql-0.5.0
As Morpheus is quite new, make sure stack can find morpheus-graphql by running stack upgrade
and stack update
Building your first GraphQL API
with GraphQL syntax
schema.gql
type Query {
deity(name: String!): Deity!
}
type Deity {
name: String!
power: String
}
API.hs
{-# LANGUAGE DeriveGeneric #-}
{-# LANGUAGE FlexibleContexts #-}
{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE MultiParamTypeClasses #-}
{-# LANGUAGE NamedFieldPuns #-}
{-# LANGUAGE OverloadedStrings #-}
{-# LANGUAGE ScopedTypeVariables #-}
{-# LANGUAGE TemplateHaskell #-}
{-# LANGUAGE TypeFamilies #-}
module API (api) where
import qualified Data.ByteString.Lazy.Char8 as B
import Data.Morpheus (interpreter)
import Data.Morpheus.Document (importGQLDocumentWithNamespace)
import Data.Morpheus.Types (GQLRootResolver (..), IORes)
import Data.Text (Text)
importGQLDocumentWithNamespace "schema.gql"
rootResolver :: GQLRootResolver IO () Query Undefined Undefined
rootResolver =
GQLRootResolver
{
queryResolver = Query {queryDeity},
mutationResolver = Undefined,
subscriptionResolver = Undefined
}
where
queryDeity QueryDeityArgs {queryDeityArgsName} = pure Deity {deityName, deityPower}
where
deityName _ = pure "Morpheus"
deityPower _ = pure (Just "Shapeshifting")
api :: ByteString -> IO ByteString
api = interpreter rootResolver
Template Haskell Generates types: Query
, Deity
, DeityArgs
, that can be used by rootResolver
importGQLDocumentWithNamespace
will generate Types with namespaced fields. if you don't need napespacing use importGQLDocument
with Native Haskell Types
To define a GraphQL API with Morpheus we start by defining the API Schema as a native Haskell data type,
which derives the Generic
typeclass. Lazily resolvable fields on this Query
type are defined via a -> IORes b
, representing resolving a set of arguments a
to a concrete value b
.
data Query m = Query
{ deity :: DeityArgs -> m Deity
} deriving (Generic, GQLType)
data Deity = Deity
{ fullName :: Text -- Non-Nullable Field
, power :: Maybe Text -- Nullable Field
} deriving (Generic)
instance GQLType Deity where
type KIND Deity = OBJECT
data DeityArgs = DeityArgs
{ name :: Text -- Required Argument
, mythology :: Maybe Text -- Optional Argument
} deriving (Generic)
For each field in the Query
type defined via a -> m b
(like deity
) we will define a resolver implementation that provides the values during runtime by referring to
some data source, e.g. a database or another API. Fields that are defined without a -> m b
you can just provide a value.
In above example, the field of DeityArgs
could also be named using reserved identities (such as: type
, where
, etc), in order to avoid conflict, a prime symbol ('
) must be attached. For example, you can have:
data DeityArgs = DeityArgs
{ name :: Text -- Required Argument
, mythology :: Maybe Text -- Optional Argument
, type' :: Text
} deriving (Generic)
The field name in the final request will be type
instead of type'
. The Morpheus request parser converts each of the reserved identities in Haskell 2010 to their corresponding names internally. This also applies to selections.
resolveDeity :: DeityArgs -> IORes Deity
resolveDeity args = QueryResolver $ ExceptT $ askDB (name args) (mythology args)
askDB :: Text -> Maybe Text -> IO (Either String Deity)
askDB = ...
Note that the type a -> IORes b
is just Synonym for a -> ExceptT String IO b
To make this Query
type available as an API, we define a GQLRootResolver
and feed it to the Morpheus interpreter
. A GQLRootResolver
consists of query
, mutation
and subscription
definitions, while we omit the latter for this example:
rootResolver :: GQLRootResolver IO () Query Undefined Undefined
rootResolver =
GQLRootResolver
{ queryResolver = Query {deity = resolveDeity}
, mutationResolver = Undefined
, subscriptionResolver = Undefined
}
gqlApi :: ByteString -> IO ByteString
gqlApi = interpreter rootResolver
As you can see, the API is defined as ByteString -> IO ByteString
which we can either invoke directly or use inside an arbitrary web framework
such as scotty
or serverless-haskell
. We'll go for scotty
in this example:
main :: IO ()
main = scotty 3000 $ post "/api" $ raw =<< (liftIO . gqlApi =<< body)
If we now send a POST request to http://localhost:3000/api
with a GraphQL Query as body for example in a tool like Insomnia
:
query GetDeity {
deity (name: "Morpheus") {
fullName
power
}
}
our query will be resolved!
{
"data": {
"deity": {
"fullName": "Morpheus",
"power": "Shapeshifting"
}
}
}
Serverless Example
If you are interested in creating a Morpheus GraphQL
API with Serverless
, you should take a look at our example in this repository:
Mythology API it is our example project build with Morpheus GraphQL
and Serverless-Haskell
,
where you can query different mythology characters with GraphiQL
.
Mythology API is deployed on : api.morpheusgraphql.com where you can test it with GraphiQL
Advanced topics
Enums
You can use Union Types as Enums, but they're not allowed to have any parameters.
data City
= Athens
| Sparta
| Corinth
| Delphi
| Argos
deriving (Generic)
instance GQLType City where
type KIND City = ENUM
Union types
To use union type, all you have to do is derive the GQLType
class. Using GraphQL fragments, the arguments of each data constructor can be accessed from the GraphQL client.
data Character
= DEITY Deity
| HUMAN Human
deriving (Generic)
instance GQLType Character where
type KIND City = UNION
Scalar types
To use custom scalar types, you need to provide implementations for parseValue
and serialize
respectively.
data Odd = Odd Int deriving (Generic)
instance GQLScalar Odd where
parseValue (Int x) = pure $ Odd (... )
parseValue (String x) = pure $ Odd (... )
serialize (Odd value) = Int value
instance GQLType Odd where
type KIND Odd = SCALAR
Applicative and Monad instance
The Resolver
type has Applicative
and Monad
instances that can be used to compose resolvers.
Introspection
Morpheus converts your schema to a GraphQL introspection automatically. You can use tools like Insomnia
to take a
look at the introspection and validate your schema.
If you need a description for your GQLType inside of the introspection you can define the GQLType instance manually
and provide an implementation for the description
function:
data Deity = Deity
{ ...
} deriving (Generic)
instance GQLType Deity where
description = const "A supernatural being considered divine and sacred"
screenshots from Insomnia
Mutations
In addition to queries, Morpheus also supports mutations. The behave just like regular queries and are defined similarly:
Just exchange deriving GQLQuery
for GQLMutation
and declare them separately at the GQLRootResolver
definition
newtype Mutation m = Mutation
{ createDeity :: Form -> m Deity
} deriving (Generic, GQLType)
createDeityMutation :: Form -> m (Deity m)
createDeityMutation = ...
rootResolver :: GQLRootResolver IO Query Mutation Undefined
rootResolver =
GQLRootResolver
{ queryResolver = Query {...}
, mutationResolver = Mutation {
createDeity = createDeityMutation
}
, subscriptionResolver = Undefined
}
gqlApi :: ByteString -> IO ByteString
gqlApi = interpreter rootResolver
Subscriptions
im morpheus subscription and mutation communicating with Events,
Event
consists with user defined Channel
and Content
.
every subscription has own Channel by which will be triggered
data Channel
= ChannelA
| ChannelB
data Content
= ContentA Int
| ContentB Text
newtype Query m = Query
{ deity :: () -> m Deity
} deriving (Generic)
newtype Mutation m = Mutation
{ createDeity :: () -> m Deity
} deriving (Generic)
newtype Subscription m = Subscription
{ newDeity :: () -> m Deity
} deriving (Generic)
type APIEvent = Event Channel Content
rootResolver :: GQLRootResolver IO APIEvent Query Mutation Subscription
rootResolver =
GQLRootResolver
{ queryResolver = Query {deity = const fetchDeity}
, mutationResolver = Mutation {createDeity}
, subscriptionResolver = Subscription {newDeity}
}
where
createDeity _args = MutResolver events updateDeity
where
events = [Event {channels = [ChannelA], content = ContentA 1}]
updateDeity = updateDBDeity
newDeity _args = SubResolver [ChannelA] subResolver
where
subResolver (Event [ChannelA] (ContentA _value)) = fetchDeity -- resolve New State
subResolver (Event [ChannelA] (ContentB _value)) = fetchDeity -- resolve New State
subResolver _ = fetchDeity -- Resolve Old State
Morpheus GraphQL Client
with Template haskell QuasiQuotes
defineByDocumentFile
"./schema.gql"
[gql|
query GetHero ($character: Character)
{
deity (fatherOf:$character) {
name
power
worships {
deity2Name: name
}
}
}
|]
with schema:
input Character {
name: String!
}
type Deity {
name: String!
worships: Deity
}
will validate query and Generate:
- namespaced response and variable types
- instance for
Fetch
typeClass
data GetHero = GetHero {
deity: DeityDeity
}
-- from: {user
data DeityDeity = DeityDeity {
name: Text,
worships: Maybe DeityWorshipsDeity
}
-- from: {deity{worships
data DeityWorshipsDeity = DeityWorshipsDeity {
name: Text,
}
data GetHeroArgs = GetHeroArgs {
getHeroArgsCharacter: Character
}
data Character = Character {
characterName: Person
}
as you see, response type field name collision can be handled with GraphQL alias
.
with fetch
you can fetch well typed response GetHero
.
fetchHero :: Args GetHero -> m (Either String GetHero)
fetchHero = fetch jsonRes args
where
args = GetHeroArgs {getHeroArgsCharacter = Person {characterName = "Zeus"}}
jsonRes :: ByteString -> m ByteString
jsonRes = <GraphQL APi>
types can be generatet from introspection
too:
defineByIntrospectionFile "./introspection.json"
Morpheus CLI for Code Generating
Generating dummy Morpheus Api from schema.gql
morpheus build src/schem.gql src/GQLApi.hs
this command will generate Haskell API and resolvers,
resolvers will resolve default values for every object
About
The name
Morpheus is the greek god of sleep and dreams whose name comes from the greek word μορφή meaning form or shape.
He is said to be able to mimic different forms and GraphQL is good at doing exactly that: Transforming data in the shape
of many different APIs.
Team
Morpheus is written and maintained by nalchevanidze
Roadmap
- Medium future:
- Stabilize API
- Specification-isomorphic error handling
- Long term:
- Support all possible GQL features
- Performance optimization