Added a tutorial, based on graphql-js and servant documentation.
This commit is contained in:
Matthías Páll Gissurarson
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pandoc -f markdown+lhs+yaml_metadata_block --highlight-style=haddock -S -c "https://maxcdn.bootstrapcdn.com/bootstrap/3.3.6/css/bootstrap.min.css" --section-divs -c tutorial.css --toc --standalone -t html5 -o tutorial.html tutorial.lhs
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pandoc -f markdown+lhs+yaml_metadata_block --highlight-style=haddock --toc --standalone -t rst -o tutorial.rst tutorial.lhs
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pandoc -f markdown+lhs+yaml_metadata_block --highlight-style=haddock --toc --standalone -t latex -o tutorial.pdf tutorial.lhs
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body {
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padding: 0 20px;
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}
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---
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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-haskell!
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We have written a small tutorial to help you (and ourselves) understand the graphql package.
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Since this file is a literate haskell file, we start by importing some dependencies.
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> {-# LANGUAGE OverloadedStrings #-}
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> {-# LANGUAGE LambdaCase #-}
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> module Main where
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>
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> import Prelude hiding (empty, putStrLn)
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> import Data.GraphQL
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> import Data.GraphQL.Schema
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> import qualified Data.GraphQL.Schema as Schema
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>
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> import Control.Applicative
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> import Data.Text hiding (empty)
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> import Data.Aeson
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> import Data.ByteString.Lazy.Char8 (putStrLn)
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>
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> import Data.Time
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>
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> import Debug.Trace
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=== First example ===
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Now, as our first example, we are going to look at the
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example from [graphql.js](https://github.com/graphql/graphql-js).
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First we build a GraphQL schema.
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> schema1 :: Alternative f => Schema f
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> schema1 = Schema [hello]
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>
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> hello :: Alternative f => Resolver f
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> hello = Schema.scalar "hello" ("it's me" :: Text)
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This defines a simple schema with one type and one field, that resolves to a 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 = putStrLn =<< encode <$> graphql schema1 query1
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This runs the query by fetching the one field defined,
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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 [time]
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>
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> time :: Resolver IO
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> time = Schema.scalarA "time" $ \case
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> [] -> do t <- getCurrentTime
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> return $ show t
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> _ -> empty
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This defines a simple schema with one type and one field,
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which resolves to the 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 = putStrLn =<< encode <$> graphql schema2 query2
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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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=== Errors ===
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Errors are handled according to the spec,
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with fields that cause erros being resolved to `null`,
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and an error being added to the error list.
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An example of this is the following query:
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> queryShouldFail :: Text
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> queryShouldFail = "{ boyhowdy }"
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Since there is no `boyhowdy` field in our schema, it will not resolve,
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and the query will fail, as we can see in the following example.
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> mainShouldFail :: IO ()
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> mainShouldFail = do
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> r <- graphql schema1 query1
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> putStrLn $ encode r
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> putStrLn "This will fail"
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> r <- graphql schema1 queryShouldFail
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> putStrLn $ encode r
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>
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This outputs:
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```
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{"data": {"hello": "it's me"}}
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This will fail
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{"data": {"boyhowdy": null}, "errors":[{"message": "the field boyhowdy did not resolve."}]}
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```
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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 [hello, time]
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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 = putStrLn =<< encode <$> graphql schema3 query3
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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 have only been using single queries, we can use the shorthand `{ time hello}`, 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 directory,
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in the [Test.StarWars](../../tests/Test/StarWars) module. This includes a more complex schema, and more complex queries.
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========================
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GraphQL Haskell Tutorial
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========================
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.. contents::
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:depth: 3
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..
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Getting started
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===============
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Welcome to graphql-haskell!
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We have written a small tutorial to help you (and ourselves) understand
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the 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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.. code:: haskell
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{-# LANGUAGE OverloadedStrings #-}
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{-# LANGUAGE LambdaCase #-}
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module Main where
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import Prelude hiding (empty, putStrLn)
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import Data.GraphQL
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import Data.GraphQL.Schema
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import qualified Data.GraphQL.Schema as Schema
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import Control.Applicative
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import Data.Text hiding (empty)
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import Data.Aeson
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import Data.ByteString.Lazy.Char8 (putStrLn)
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import Data.Time
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import Debug.Trace
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First example
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-------------
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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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.. code:: haskell
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schema1 :: Alternative f => Schema f
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schema1 = Schema [hello]
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hello :: Alternative f => Resolver f
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hello = Schema.scalar "hello" ("it's me" :: Text)
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This defines a simple schema with one type and one field, that resolves
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to a fixed value.
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Next we define our query.
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.. code:: haskell
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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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.. code:: haskell
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main1 :: IO ()
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main1 = putStrLn =<< encode <$> graphql schema1 query1
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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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---------------
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For this example, we're going to be using time.
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.. code:: haskell
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schema2 :: Schema IO
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schema2 = Schema [time]
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time :: Resolver IO
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time = Schema.scalarA "time" $ \case
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[] -> do t <- getCurrentTime
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return $ show t
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_ -> empty
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This defines a simple schema with one type and one field, which resolves
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to the current time.
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Next we define our query.
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.. code:: haskell
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query2 :: Text
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query2 = "{ time }"
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main2 :: IO ()
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main2 = putStrLn =<< encode <$> graphql schema2 query2
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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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Errors
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------
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Errors are handled according to the spec, with fields that cause erros
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being resolved to ``null``, and an error being added to the error list.
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An example of this is the following query:
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.. code:: haskell
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queryShouldFail :: Text
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queryShouldFail = "{ boyhowdy }"
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Since there is no ``boyhowdy`` field in our schema, it will not resolve,
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and the query will fail, as we can see in the following example.
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.. code:: haskell
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mainShouldFail :: IO ()
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mainShouldFail = do
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r <- graphql schema1 query1
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putStrLn $ encode r
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putStrLn "This will fail"
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r <- graphql schema1 queryShouldFail
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putStrLn $ encode r
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This outputs:
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::
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{"data": {"hello": "it's me"}}
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This will fail
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{"data": {"boyhowdy": null}, "errors":[{"message": "the field boyhowdy did not resolve."}]}
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Combining resolvers
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-------------------
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Now that we have two resolvers, we can define a schema which uses them
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both.
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.. code:: haskell
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schema3 :: Schema IO
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schema3 = Schema [hello, time]
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query3 :: Text
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query3 = "query timeAndHello { time hello }"
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main3 :: IO ()
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main3 = putStrLn =<< encode <$> graphql schema3 query3
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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``.
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Since we have only been using single queries, we can use the shorthand
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``{ time hello}``, 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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================
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More examples on queries and a more complex schema can be found in the
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test directory, in the `Test.StarWars <../../tests/Test/StarWars>`__
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module. This includes a more complex schema, and more complex queries.
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