<!DOCTYPE html>
<!--[if IE 8]><html class="no-js lt-ie9" lang="en" > <![endif]-->
<!--[if gt IE 8]><!--> <html class="no-js" lang="en" > <!--<![endif]-->
<head>
<meta charset="utf-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<link rel="shortcut icon" href="../img/favicon.ico">
<title>Fetching Data - graphql-php</title>
<link href='https://fonts.googleapis.com/css?family=Lato:400,700|Roboto+Slab:400,700|Inconsolata:400,700' rel='stylesheet' type='text/css'>
<link rel="stylesheet" href="../css/theme.css" type="text/css" />
<link rel="stylesheet" href="../css/theme_extra.css" type="text/css" />
<link rel="stylesheet" href="../css/highlight.css">
<script>
// Current page data
var mkdocs_page_name = "Fetching Data";
var mkdocs_page_input_path = "data-fetching.md";
var mkdocs_page_url = "/data-fetching/";
</script>
<script src="../js/jquery-2.1.1.min.js"></script>
<script src="../js/modernizr-2.8.3.min.js"></script>
<script type="text/javascript" src="../js/highlight.pack.js"></script>
</head>
<body class="wy-body-for-nav" role="document">
<div class="wy-grid-for-nav">
<nav data-toggle="wy-nav-shift" class="wy-nav-side stickynav">
<div class="wy-side-nav-search">
<a href=".." class="icon icon-home"> graphql-php</a>
<div role="search">
<form id ="rtd-search-form" class="wy-form" action="../search.html" method="get">
<input type="text" name="q" placeholder="Search docs" />
</form>
</div>
</div>
<div class="wy-menu wy-menu-vertical" data-spy="affix" role="navigation" aria-label="main navigation">
<ul class="current">
<li class="toctree-l1">
<a class="" href="..">About</a>
</li>
<li class="toctree-l1">
<a class="" href="../getting-started/">Getting Started</a>
</li>
<li class="toctree-l1">
<span class="caption-text">Type System</span>
<ul class="subnav">
<li class="">
<a class="" href="../type-system/">Introduction</a>
</li>
<li class="">
<a class="" href="../type-system/object-types/">Object Types</a>
</li>
<li class="">
<a class="" href="../type-system/scalar-types/">Scalar Types</a>
</li>
<li class="">
<a class="" href="../type-system/enum-types/">Enumeration Types</a>
</li>
<li class="">
<a class="" href="../type-system/lists-and-nonnulls/">Lists and Non-Null</a>
</li>
<li class="">
<a class="" href="../type-system/interfaces/">Interfaces</a>
</li>
<li class="">
<a class="" href="../type-system/unions/">Unions</a>
</li>
<li class="">
<a class="" href="../type-system/input-types/">Input Types</a>
</li>
<li class="">
<a class="" href="../type-system/directives/">Directives</a>
</li>
<li class="">
<a class="" href="../type-system/schema/">Schema</a>
</li>
</ul>
</li>
<li class="toctree-l1">
<a class="" href="../executing-queries/">Executing Queries</a>
</li>
<li class="toctree-l1 current">
<a class="current" href="./">Fetching Data</a>
<ul class="subnav">
<li class="toctree-l2"><a href="#overview">Overview</a></li>
<li class="toctree-l2"><a href="#default-field-resolver">Default Field Resolver</a></li>
<li class="toctree-l2"><a href="#default-field-resolver-per-type">Default Field Resolver per Type</a></li>
<li class="toctree-l2"><a href="#solving-n1-problem">Solving N+1 Problem</a></li>
<li class="toctree-l2"><a href="#async-php">Async PHP</a></li>
</ul>
</li>
<li class="toctree-l1">
<a class="" href="../error-handling/">Handling Errors</a>
</li>
<li class="toctree-l1">
<a class="" href="../complementary-tools/">Complementary Tools</a>
</li>
</ul>
</div>
</nav>
<section data-toggle="wy-nav-shift" class="wy-nav-content-wrap">
<nav class="wy-nav-top" role="navigation" aria-label="top navigation">
<i data-toggle="wy-nav-top" class="fa fa-bars"></i>
<a href="..">graphql-php</a>
</nav>
<div class="wy-nav-content">
<div class="rst-content">
<div role="navigation" aria-label="breadcrumbs navigation">
<ul class="wy-breadcrumbs">
<li><a href="..">Docs</a> »</li>
<li>Fetching Data</li>
<li class="wy-breadcrumbs-aside">
</li>
</ul>
<hr/>
</div>
<div role="main">
<div class="section">
<h1 id="overview">Overview</h1>
<p>GraphQL is data-storage agnostic. You can use any underlying data storage engine, including SQL or NoSQL database,
plain files or in-memory data structures.</p>
<p>In order to convert GraphQL query to PHP array <strong>graphql-php</strong> traverses query fields (using depth-first algorithm) and
runs special <code>resolve</code> function on each field. This <code>resolve</code> function is provided by you as a part of
<a href="../type-system/object-types/#field-configuration-options">field definition</a>.</p>
<p>Result returned by <code>resolve</code> function is directly included in response (for scalars and enums)
or passed down to nested fields (for objects).</p>
<p>Let's walk through an example. Consider following GraphQL query:</p>
<pre><code class="graphql">{
lastStory {
title
author {
name
}
}
}
</code></pre>
<p>We need Schema that can fulfill it. On the very top level Schema contains Query type:</p>
<pre><code class="php">$queryType = new ObjectType([
'name' => 'Query',
'fields' => [
'lastStory' => [
'type' => $blogStoryType,
'resolve' => function() {
return [
'id' => 1,
'title' => 'Example blog post',
'authorId' => 1
];
}
]
]
]);
</code></pre>
<p>As we see field <code>lastStory</code> has <code>resolve</code> function that is responsible for fetching data.</p>
<p>In our example we simply return array value, but in real-world application you would query
your database/cache/search index and return result.</p>
<p>Since <code>lastStory</code> is of complex type <code>BlogStory</code> this result is passed down to fields of this type:</p>
<pre><code class="php">$blogStoryType = new ObjectType([
'name' => 'BlogStory',
'fields' => [
'author' => [
'type' => $userType,
'resolve' => function($blogStory) {
$users = [
1 => [
'id' => 1,
'name' => 'Smith'
],
2 => [
'id' => 2,
'name' => 'Anderson'
]
];
return $users[$blogStory['authorId']];
}
],
'title' => [
'type' => Type::string()
]
]
]);
</code></pre>
<p>Here <code>$blogStory</code> is the array returned by <code>lastStory</code> field above. </p>
<p>Again: in real-world applications you would fetch user data from datastore by <code>authorId</code> and return it.
Also note that you don't have to return arrays. You can return any value, <strong>graphql-php</strong> will pass it untouched
to nested resolvers.</p>
<p>But then the question appears - field <code>title</code> has no <code>resolve</code> option. How is it resolved?</p>
<p>The answer is: there is default resolver for all fields. When you define your own <code>resolve</code> function
for a field you simply override this default resolver.</p>
<h1 id="default-field-resolver">Default Field Resolver</h1>
<p><strong>graphql-php</strong> provides following default field resolver:</p>
<pre><code class="php">function defaultFieldResolver($source, $args, $context, ResolveInfo $info)
{
$fieldName = $info->fieldName;
$property = null;
if (is_array($source) || $source instanceof \ArrayAccess) {
if (isset($source[$fieldName])) {
$property = $source[$fieldName];
}
} else if (is_object($source)) {
if (isset($source->{$fieldName})) {
$property = $source->{$fieldName};
}
}
return $property instanceof \Closure ? $property($source, $args, $context) : $property;
}
</code></pre>
<p>As you see it returns value by key (for arrays) or property (for objects). If value is not set - it returns <code>null</code>.</p>
<p>To override default resolver - use:</p>
<pre><code class="php">GraphQL\GraphQL::setDefaultFieldResolver($myResolverCallback);
</code></pre>
<h1 id="default-field-resolver-per-type">Default Field Resolver per Type</h1>
<p>Sometimes it might be convenient to set default field resolver per type. You can do so by providing
<a href="../type-system/object-types/#configuration-options">resolveField option in type config</a>. For example:</p>
<pre><code class="php">$userType = new ObjectType([
'name' => 'User',
'fields' => [
'name' => Type::string(),
'email' => Type::string()
],
'resolveField' => function(User $user, $args, $context, ResolveInfo $info) {
switch ($info->fieldName) {
case 'name':
return $user->getName();
case 'email':
return $user->getEmail();
default:
return null;
}
}
]);
</code></pre>
<p>Keep in mind that <strong>field resolver</strong> has precedence over <strong>default field resolver per type</strong> which in turn
has precedence over <strong>default field resolver</strong>.</p>
<h1 id="solving-n1-problem">Solving N+1 Problem</h1>
<p>Since: 0.9.0</p>
<p>One of the most annoying problems with data fetching is so-called <a href="https://secure.phabricator.com/book/phabcontrib/article/n_plus_one/">N+1 problem</a>.</p>
<p>Consider following GraphQL query:</p>
<pre><code>{
topStories(limit: 10) {
title
author {
name
email
}
}
}
</code></pre>
<p>Naive field resolution process would require up to 10 calls to underlying data store to fetch authors for all 10 stories.</p>
<p><strong>graphql-php</strong> provides tools to mitigate this problem: it allows you to defer actual field resolution to later stage
when one batched query could be executed instead of 10 distinct queries.</p>
<p>Here is an example of <code>BlogStory</code> resolver for field <code>author</code> that uses deferring:</p>
<pre><code class="php">'resolve' => function($blogStory) {
MyUserBuffer::add($blogStory['authorId']);
return new GraphQL\Deferred(function () use ($blogStory) {
MyUserBuffer::loadBuffered();
return MyUserBuffer::get($blogStory['authorId']);
});
}
</code></pre>
<p>In this example we fill up buffer with 10 author ids first. Then <strong>graphql-php</strong> continues
resolving other non-deferred fields until there are none of them left.</p>
<p>After that it calls <code>Closures</code> wrapped by <code>GraphQL\Deferred</code> which in turn load all buffered
ids once (using SQL IN(?), Redis MGET or other similar tools) and return final field value.</p>
<p>Originally this approach was advocated by Facebook in their <a href="https://github.com/facebook/dataloader">Dataloader</a>
project.</p>
<p>This solution enables very interesting optimizations at no cost. Consider following query:</p>
<pre><code>{
topStories(limit: 10) {
author {
email
}
}
category {
stories(limit: 10) {
author {
email
}
}
}
}
</code></pre>
<p>Even if <code>author</code> field is located on different levels of query - it can be buffered in the same buffer.
In this example only one query will be executed for all story authors comparing to 20 queries
in naive implementation.</p>
<h1 id="async-php">Async PHP</h1>
<p>Since: 0.9.0</p>
<p>If your project runs in environment that supports async operations
(like <code>HHVM</code>, <code>ReactPHP</code>, <code>Icicle.io</code>, <code>appserver.io</code> <code>PHP threads</code>, etc) you can leverage
the power of your platform to resolve fields asynchronously.</p>
<p>The only requirement: your platform must support the concept of Promises compatible with
<a href="https://promisesaplus.com/">Promises A+</a> specification.</p>
<p>To enable async support - set adapter for promises:</p>
<pre><code>GraphQL\GraphQL::setPromiseAdapter($adapter);
</code></pre>
<p>Where <code>$adapter</code> is an instance of class implementing <code>GraphQL\Executor\Promise\PromiseAdapter</code> interface.</p>
<p>Then in your <code>resolve</code> functions you should return <code>Promises</code> of your platform instead of
<code>GraphQL\Deferred</code> instances.</p>
<p>Platforms supported out of the box:</p>
<ul>
<li><a href="https://github.com/reactphp/react">ReactPHP</a> (requires <strong>react/promise</strong> as composer dependency):
<code>GraphQL\GraphQL::setPromiseAdapter(new GraphQL\Executor\Promise\Adapter\ReactPromiseAdapter());</code></li>
</ul>
<p>To integrate other platform - implement <code>GraphQL\Executor\Promise\PromiseAdapter</code> interface. </p>
</div>
</div>
<footer>
<div class="rst-footer-buttons" role="navigation" aria-label="footer navigation">
<a href="../error-handling/" class="btn btn-neutral float-right" title="Handling Errors">Next <span class="icon icon-circle-arrow-right"></span></a>
<a href="../executing-queries/" class="btn btn-neutral" title="Executing Queries"><span class="icon icon-circle-arrow-left"></span> Previous</a>
</div>
<hr/>
<div role="contentinfo">
<!-- Copyright etc -->
</div>
Built with <a href="http://www.mkdocs.org">MkDocs</a> using a <a href="https://github.com/snide/sphinx_rtd_theme">theme</a> provided by <a href="https://readthedocs.org">Read the Docs</a>.
</footer>
</div>
</div>
</section>
</div>
<div class="rst-versions" role="note" style="cursor: pointer">
<span class="rst-current-version" data-toggle="rst-current-version">
<span><a href="../executing-queries/" style="color: #fcfcfc;">« Previous</a></span>
<span style="margin-left: 15px"><a href="../error-handling/" style="color: #fcfcfc">Next »</a></span>
</span>
</div>
<script src="../js/theme.js"></script>
</body>
</html>