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</style> - <link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.6/css/bootstrap.min.css"> - <link rel="stylesheet" href="tutorial.css"> - <!--[if lt IE 9]> - <script src="//cdnjs.cloudflare.com/ajax/libs/html5shiv/3.7.3/html5shiv-printshiv.min.js"></script> - <![endif]--> -</head> -<body> -<header> -<h1 class="title">GraphQL Haskell Tutorial</h1> -</header> -<nav id="TOC"> -<ul> -<li><a href="#getting-started">Getting started</a><ul> -<li><a href="#first-example">First example</a></li> -<li><a href="#monadic-actions">Monadic actions</a></li> -<li><a href="#errors">Errors</a></li> -<li><a href="#combining-resolvers">Combining resolvers</a></li> -</ul></li> -<li><a href="#further-examples">Further examples</a></li> -</ul> -</nav> -<section id="getting-started" class="level2"> -<h2>Getting started</h2> -<p>Welcome to graphql-haskell!</p> -<p>We have written a small tutorial to help you (and ourselves) understand the graphql package.</p> -<p>Since this file is a literate haskell file, we start by importing some dependencies.</p> -<div class="sourceCode"><pre class="sourceCode literate haskell"><code class="sourceCode haskell"><span class="ot">{-# LANGUAGE OverloadedStrings #-}</span> -<span class="ot">{-# LANGUAGE LambdaCase #-}</span> -<span class="kw">module</span> <span class="dt">Main</span> <span class="kw">where</span> - -<span class="kw">import </span><span class="dt">Prelude</span> <span class="kw">hiding</span> (empty, putStrLn) -<span class="kw">import </span><span class="dt">Data.GraphQL</span> -<span class="kw">import </span><span class="dt">Data.GraphQL.Schema</span> -<span class="kw">import qualified</span> <span class="dt">Data.GraphQL.Schema</span> <span class="kw">as</span> <span class="dt">Schema</span> - -<span class="kw">import </span><span class="dt">Control.Applicative</span> -<span class="kw">import </span><span class="dt">Data.List.NonEmpty</span> (<span class="dt">NonEmpty</span>((:|))) -<span class="kw">import </span><span class="dt">Data.Text</span> <span class="kw">hiding</span> (empty) -<span class="kw">import </span><span class="dt">Data.Aeson</span> -<span class="kw">import </span><span class="dt">Data.ByteString.Lazy.Char8</span> (putStrLn) - -<span class="kw">import </span><span class="dt">Data.Time</span> - -<span class="kw">import </span><span class="dt">Debug.Trace</span></code></pre></div> -<section id="first-example" class="level3"> -<h3>First example</h3> -<p>Now, as our first example, we are going to look at the example from <a href="https://github.com/graphql/graphql-js">graphql.js</a>.</p> -<p>First we build a GraphQL schema.</p> -<div class="sourceCode"><pre class="sourceCode literate haskell"><code class="sourceCode haskell"><span class="ot">schema1 ::</span> <span class="dt">Alternative</span> f <span class="ot">=></span> <span class="dt">Schema</span> f -schema1 <span class="fu">=</span> hello <span class="fu">:|</span> [] - -<span class="ot">hello ::</span> <span class="dt">Alternative</span> f <span class="ot">=></span> <span class="dt">Resolver</span> f -hello <span class="fu">=</span> Schema.scalar <span class="st">"hello"</span> (<span class="st">"it's me"</span><span class="ot"> ::</span> <span class="dt">Text</span>)</code></pre></div> -<p>This defines a simple schema with one type and one field, that resolves to a fixed value.</p> -<p>Next we define our query.</p> -<div class="sourceCode"><pre class="sourceCode literate haskell"><code class="sourceCode haskell"><span class="ot">query1 ::</span> <span class="dt">Text</span> -query1 <span class="fu">=</span> <span class="st">"{ hello }"</span></code></pre></div> -<p>To run the query, we call the <code>graphql</code> with the schema and the query.</p> -<div class="sourceCode"><pre class="sourceCode literate haskell"><code class="sourceCode haskell"><span class="ot">main1 ::</span> <span class="dt">IO</span> () -main1 <span class="fu">=</span> putStrLn <span class="fu">=<<</span> encode <span class="fu"><$></span> graphql schema1 query1</code></pre></div> -<p>This runs the query by fetching the one field defined, returning</p> -<p><code>{"data" : {"hello":"it's me"}}</code></p> -</section> -<section id="monadic-actions" class="level3"> -<h3>Monadic actions</h3> -<p>For this example, we’re going to be using time.</p> -<div class="sourceCode"><pre class="sourceCode literate haskell"><code class="sourceCode haskell"><span class="ot">schema2 ::</span> <span class="dt">Schema</span> <span class="dt">IO</span> -schema2 <span class="fu">=</span> time <span class="fu">:|</span> [] - -<span class="ot">time ::</span> <span class="dt">Resolver</span> <span class="dt">IO</span> -time <span class="fu">=</span> Schema.scalarA <span class="st">"time"</span> <span class="fu">$</span> \<span class="kw">case</span> - [] <span class="ot">-></span> <span class="kw">do</span> t <span class="ot"><-</span> getCurrentTime - return <span class="fu">$</span> show t - _ <span class="ot">-></span> empty</code></pre></div> -<p>This defines a simple schema with one type and one field, which resolves to the current time.</p> -<p>Next we define our query.</p> -<div class="sourceCode"><pre class="sourceCode literate haskell"><code class="sourceCode haskell"><span class="ot">query2 ::</span> <span class="dt">Text</span> -query2 <span class="fu">=</span> <span class="st">"{ time }"</span> - -<span class="ot">main2 ::</span> <span class="dt">IO</span> () -main2 <span class="fu">=</span> putStrLn <span class="fu">=<<</span> encode <span class="fu"><$></span> graphql schema2 query2</code></pre></div> -<p>This runs the query, returning the current time</p> -<p><code>{"data": {"time":"2016-03-08 23:28:14.546899 UTC"}}</code></p> -</section> -<section id="errors" class="level3"> -<h3>Errors</h3> -<p>Errors are handled according to the spec, with fields that cause erros being resolved to <code>null</code>, and an error being added to the error list.</p> -<p>An example of this is the following query:</p> -<div class="sourceCode"><pre class="sourceCode literate haskell"><code class="sourceCode haskell"><span class="ot">queryShouldFail ::</span> <span class="dt">Text</span> -queryShouldFail <span class="fu">=</span> <span class="st">"{ boyhowdy }"</span></code></pre></div> -<p>Since there is no <code>boyhowdy</code> field in our schema, it will not resolve, and the query will fail, as we can see in the following example.</p> -<div class="sourceCode"><pre class="sourceCode literate haskell"><code class="sourceCode haskell"><span class="ot">mainShouldFail ::</span> <span class="dt">IO</span> () -mainShouldFail <span class="fu">=</span> <span class="kw">do</span> - r <span class="ot"><-</span> graphql schema1 query1 - putStrLn <span class="fu">$</span> encode r - putStrLn <span class="st">"This will fail"</span> - r <span class="ot"><-</span> graphql schema1 queryShouldFail - putStrLn <span class="fu">$</span> encode r</code></pre></div> -<p>This outputs:</p> -<pre><code>{"data": {"hello": "it's me"}} -This will fail -{"data": {"boyhowdy": null}, "errors":[{"message": "the field boyhowdy did not resolve."}]}</code></pre> -</section> -<section id="combining-resolvers" class="level3"> -<h3>Combining resolvers</h3> -<p>Now that we have two resolvers, we can define a schema which uses them both.</p> -<div class="sourceCode"><pre class="sourceCode literate haskell"><code class="sourceCode haskell"><span class="ot">schema3 ::</span> <span class="dt">Schema</span> <span class="dt">IO</span> -schema3 <span class="fu">=</span> hello <span class="fu">:|</span> [time] - -<span class="ot">query3 ::</span> <span class="dt">Text</span> -query3 <span class="fu">=</span> <span class="st">"query timeAndHello { time hello }"</span> - -<span class="ot">main3 ::</span> <span class="dt">IO</span> () -main3 <span class="fu">=</span> putStrLn <span class="fu">=<<</span> encode <span class="fu"><$></span> graphql schema3 query3</code></pre></div> -<p>This queries for both time and hello, returning</p> -<p><code>{ "data": {"hello":"it's me","time":"2016-03-08 23:29:11.62108 UTC"}}</code></p> -<p>Notice that we can name our queries, as we did with <code>timeAndHello</code>. Since we have only been using single queries, we can use the shorthand <code>{ time hello}</code>, as we have been doing in the previous examples.</p> -<p>In GraphQL there can only be one operation per query.</p> -</section> -</section> -<section id="further-examples" class="level2"> -<h2>Further examples</h2> -<p>More examples on queries and a more complex schema can be found in the test directory, in the <a href="../../tests/Test/StarWars">Test.StarWars</a> module. This includes a more complex schema, and more complex queries.</p> -</section> -</body> -</html> |