1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
|
---
title: GraphQL Haskell Tutorial
---
== Getting started ==
Welcome to GraphQL!
We have written a small tutorial to help you (and ourselves) understand the
graphql package.
Since this file is a literate haskell file, we start by importing some
dependencies.
> {-# LANGUAGE OverloadedStrings #-}
> module Main where
>
> import Control.Monad.IO.Class (liftIO)
> import Data.Aeson (encode)
> import Data.ByteString.Lazy.Char8 (putStrLn)
> import qualified Data.HashMap.Strict as HashMap
> import Data.Text (Text)
> import qualified Data.Text as Text
> import Data.Time (getCurrentTime)
>
> import Language.GraphQL
> import Language.GraphQL.Type
> import qualified Language.GraphQL.Type.Out as Out
>
> import Prelude hiding (putStrLn)
=== First example ===
Now, as our first example, we are going to look at the example from
[graphql.js](https://github.com/graphql/graphql-js).
First we build a GraphQL schema.
> schema1 :: Schema IO
> schema1 = schema queryType Nothing Nothing mempty
>
> queryType :: ObjectType IO
> queryType = ObjectType "Query" Nothing []
> $ HashMap.singleton "hello"
> $ ValueResolver helloField hello
>
> helloField :: Field IO
> helloField = Field Nothing (Out.NamedScalarType string) mempty
>
> hello :: Resolve IO
> hello = pure $ String "it's me"
This defines a simple schema with one type and one field, that resolves to a
fixed value.
Next we define our query.
> query1 :: Text
> query1 = "{ hello }"
To run the query, we call the `graphql` with the schema and the query.
> main1 :: IO ()
> main1 = graphql schema1 query1
> >>= either (const $ pure ()) (putStrLn . encode)
This runs the query by fetching the one field defined, returning
```{"data" : {"hello":"it's me"}}```
=== Monadic actions ===
For this example, we're going to be using time.
> schema2 :: Schema IO
> schema2 = schema queryType2 Nothing Nothing mempty
>
> queryType2 :: ObjectType IO
> queryType2 = ObjectType "Query" Nothing []
> $ HashMap.singleton "time"
> $ ValueResolver timeField time
>
> timeField :: Field IO
> timeField = Field Nothing (Out.NamedScalarType string) mempty
>
> time :: Resolve IO
> time = do
> t <- liftIO getCurrentTime
> pure $ String $ Text.pack $ show t
This defines a simple schema with one type and one field, which resolves to the
current time.
Next we define our query.
> query2 :: Text
> query2 = "{ time }"
>
> main2 :: IO ()
> main2 = graphql schema2 query2
> >>= either (const $ pure ()) (putStrLn . encode)
This runs the query, returning the current time
```{"data": {"time":"2016-03-08 23:28:14.546899 UTC"}}```
=== Combining resolvers ===
Now that we have two resolvers, we can define a schema which uses them both.
> schema3 :: Schema IO
> schema3 = schema queryType3 Nothing Nothing mempty
>
> queryType3 :: ObjectType IO
> queryType3 = ObjectType "Query" Nothing [] $ HashMap.fromList
> [ ("hello", ValueResolver helloField hello)
> , ("time", ValueResolver timeField time)
> ]
>
> query3 :: Text
> query3 = "query timeAndHello { time hello }"
>
> main3 :: IO ()
> main3 = graphql schema3 query3
> >>= either (const $ pure ()) (putStrLn . encode)
This queries for both time and hello, returning
```{ "data": {"hello":"it's me","time":"2016-03-08 23:29:11.62108 UTC"}}```
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.
In GraphQL there can only be one operation per query.
== Further examples ==
More examples on queries and a more complex schema can be found in the test
directory, in the [Test.StarWars](../../tests/Test/StarWars) module. This
includes a more complex schema, and more complex queries.
> main :: IO ()
> main = main1 >> main2 >> main3
|
