153 lines
3.8 KiB
Plaintext
153 lines
3.8 KiB
Plaintext
---
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title: GraphQL Haskell Tutorial
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---
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== Getting started ==
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Welcome to GraphQL!
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We have written a small tutorial to help you (and ourselves) understand the
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graphql package.
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Since this file is a literate haskell file, we start by importing some
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dependencies.
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> {-# LANGUAGE OverloadedStrings #-}
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> module Main where
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>
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> import Control.Monad.IO.Class (liftIO)
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> import Data.Aeson (encode)
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> import Data.ByteString.Lazy.Char8 (putStrLn)
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> import qualified Data.HashMap.Strict as HashMap
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> import Data.Text (Text)
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> import qualified Data.Text as Text
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> import Data.Time (getCurrentTime)
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>
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> import Language.GraphQL
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> import Language.GraphQL.Type
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> import qualified Language.GraphQL.Type.Out as Out
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>
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> import Prelude hiding (putStrLn)
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=== First example ===
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Now, as our first example, we are going to look at the example from
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[graphql.js](https://github.com/graphql/graphql-js).
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First we build a GraphQL schema.
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> schema1 :: Schema IO
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> schema1 = Schema
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> { query = queryType , mutation = Nothing , subscription = Nothing }
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>
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> queryType :: ObjectType IO
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> queryType = ObjectType "Query" Nothing []
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> $ HashMap.singleton "hello"
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> $ ValueResolver helloField hello
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>
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> helloField :: Field IO
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> helloField = Field Nothing (Out.NamedScalarType string) mempty
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>
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> hello :: Resolve IO
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> hello = pure $ String "it's me"
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This defines a simple schema with one type and one field, that resolves to a
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fixed value.
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Next we define our query.
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> query1 :: Text
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> query1 = "{ hello }"
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To run the query, we call the `graphql` with the schema and the query.
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> main1 :: IO ()
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> main1 = graphql schema1 query1
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> >>= either (const $ pure ()) (putStrLn . encode)
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This runs the query by fetching the one field defined, returning
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```{"data" : {"hello":"it's me"}}```
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=== Monadic actions ===
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For this example, we're going to be using time.
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> schema2 :: Schema IO
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> schema2 = Schema
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> { query = queryType2, mutation = Nothing, subscription = Nothing }
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>
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> queryType2 :: ObjectType IO
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> queryType2 = ObjectType "Query" Nothing []
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> $ HashMap.singleton "time"
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> $ ValueResolver timeField time
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>
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> timeField :: Field IO
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> timeField = Field Nothing (Out.NamedScalarType string) mempty
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>
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> time :: Resolve IO
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> time = do
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> t <- liftIO getCurrentTime
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> pure $ String $ Text.pack $ show t
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This defines a simple schema with one type and one field, which resolves to the
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current time.
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Next we define our query.
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> query2 :: Text
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> query2 = "{ time }"
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>
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> main2 :: IO ()
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> main2 = graphql schema2 query2
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> >>= either (const $ pure ()) (putStrLn . encode)
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This runs the query, returning the current time
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```{"data": {"time":"2016-03-08 23:28:14.546899 UTC"}}```
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=== Combining resolvers ===
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Now that we have two resolvers, we can define a schema which uses them both.
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> schema3 :: Schema IO
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> schema3 = Schema
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> { query = queryType3, mutation = Nothing, subscription = Nothing }
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>
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> queryType3 :: ObjectType IO
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> queryType3 = ObjectType "Query" Nothing [] $ HashMap.fromList
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> [ ("hello", ValueResolver helloField hello)
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> , ("time", ValueResolver timeField time)
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> ]
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>
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> query3 :: Text
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> query3 = "query timeAndHello { time hello }"
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>
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> main3 :: IO ()
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> main3 = graphql schema3 query3
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> >>= either (const $ pure ()) (putStrLn . encode)
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This queries for both time and hello, returning
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```{ "data": {"hello":"it's me","time":"2016-03-08 23:29:11.62108 UTC"}}```
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Notice that we can name our queries, as we did with `timeAndHello`. Since we
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have only been using single queries, we can use the shorthand `{ time hello }`,
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as we have been doing in the previous examples.
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In GraphQL there can only be one operation per query.
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== Further examples ==
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More examples on queries and a more complex schema can be found in the test
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directory, in the [Test.StarWars](../../tests/Test/StarWars) module. This
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includes a more complex schema, and more complex queries.
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> main :: IO ()
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> main = main1 >> main2 >> main3
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