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<li class="toctree-l2"><a href="#overview">Overview</a></li>
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<h1 id="overview">Overview</h1>
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<p>GraphQL is data-storage agnostic. You can use any underlying data storage engine, including SQL or NoSQL database,
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plain files or in-memory data structures.</p>
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<p>In order to convert the GraphQL query to PHP array, <strong>graphql-php</strong> traverses query fields (using depth-first algorithm) and
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runs special <strong>resolve</strong> function on each field. This <strong>resolve</strong> function is provided by you as a part of
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<a href="../type-system/object-types/#field-configuration-options">field definition</a> or <a href="../executing-queries/#overview">query execution call</a>.</p>
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<p>Result returned by <strong>resolve</strong> function is directly included in the response (for scalars and enums)
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or passed down to nested fields (for objects).</p>
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<p>Let's walk through an example. Consider following GraphQL query:</p>
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<pre><code class="graphql">{
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lastStory {
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title
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author {
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name
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}
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}
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}
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</code></pre>
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<p>We need a Schema that can fulfill it. On the very top level the Schema contains Query type:</p>
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<pre><code class="php"><?php
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use GraphQL\Type\Definition\ObjectType;
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$queryType = new ObjectType([
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'name' => 'Query',
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'fields' => [
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'lastStory' => [
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'type' => $blogStoryType,
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'resolve' => function() {
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return [
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'id' => 1,
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'title' => 'Example blog post',
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'authorId' => 1
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];
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}
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]
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]
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]);
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</code></pre>
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<p>As we see field <strong>lastStory</strong> has <strong>resolve</strong> function that is responsible for fetching data.</p>
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<p>In our example, we simply return array value, but in the real-world application you would query
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your database/cache/search index and return the result.</p>
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<p>Since <strong>lastStory</strong> is of composite type <strong>BlogStory</strong> this result is passed down to fields of this type:</p>
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<pre><code class="php"><?php
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use GraphQL\Type\Definition\Type;
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use GraphQL\Type\Definition\ObjectType;
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$blogStoryType = new ObjectType([
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'name' => 'BlogStory',
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'fields' => [
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'author' => [
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'type' => $userType,
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'resolve' => function($blogStory) {
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$users = [
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1 => [
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'id' => 1,
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'name' => 'Smith'
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],
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2 => [
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'id' => 2,
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'name' => 'Anderson'
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]
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];
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return $users[$blogStory['authorId']];
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}
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],
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'title' => [
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'type' => Type::string()
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]
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]
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]);
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</code></pre>
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<p>Here <strong>$blogStory</strong> is the array returned by <strong>lastStory</strong> field above. </p>
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<p>Again: in the real-world applications you would fetch user data from data store by <strong>authorId</strong> and return it.
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Also, note that you don't have to return arrays. You can return any value, <strong>graphql-php</strong> will pass it untouched
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to nested resolvers.</p>
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<p>But then the question appears - field <strong>title</strong> has no <strong>resolve</strong> option. How is it resolved?</p>
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<p>There is a default resolver for all fields. When you define your own <strong>resolve</strong> function
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for a field you simply override this default resolver.</p>
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<h1 id="default-field-resolver">Default Field Resolver</h1>
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<p><strong>graphql-php</strong> provides following default field resolver:</p>
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<pre><code class="php"><?php
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function defaultFieldResolver($source, $args, $context, \GraphQL\Type\Definition\ResolveInfo $info)
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{
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$fieldName = $info->fieldName;
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$property = null;
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if (is_array($source) || $source instanceof \ArrayAccess) {
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if (isset($source[$fieldName])) {
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$property = $source[$fieldName];
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}
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} else if (is_object($source)) {
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if (isset($source->{$fieldName})) {
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$property = $source->{$fieldName};
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}
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}
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return $property instanceof \Closure ? $property($source, $args, $context) : $property;
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}
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</code></pre>
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<p>As you see it returns value by key (for arrays) or property (for objects).
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If the value is not set - it returns <strong>null</strong>.</p>
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<p>To override the default resolver, pass it as an argument of <a href="../executing-queries/">executeQuery</a> call.</p>
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<h1 id="default-field-resolver-per-type">Default Field Resolver per Type</h1>
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<p>Sometimes it might be convenient to set default field resolver per type. You can do so by providing
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<a href="../type-system/object-types/#configuration-options">resolveField option in type config</a>. For example:</p>
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<pre><code class="php"><?php
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use GraphQL\Type\Definition\Type;
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use GraphQL\Type\Definition\ObjectType;
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use GraphQL\Type\Definition\ResolveInfo;
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$userType = new ObjectType([
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'name' => 'User',
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'fields' => [
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'name' => Type::string(),
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'email' => Type::string()
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],
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'resolveField' => function(User $user, $args, $context, ResolveInfo $info) {
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switch ($info->fieldName) {
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case 'name':
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return $user->getName();
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case 'email':
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return $user->getEmail();
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default:
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return null;
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}
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}
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]);
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</code></pre>
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<p>Keep in mind that <strong>field resolver</strong> has precedence over <strong>default field resolver per type</strong> which in turn
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has precedence over <strong>default field resolver</strong>.</p>
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<h1 id="solving-n1-problem">Solving N+1 Problem</h1>
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<p>Since: 0.9.0</p>
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<p>One of the most annoying problems with data fetching is a so-called
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<a href="https://secure.phabricator.com/book/phabcontrib/article/n_plus_one/">N+1 problem</a>. <br>
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Consider following GraphQL query:</p>
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<pre><code>{
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topStories(limit: 10) {
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title
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author {
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name
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email
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}
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}
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}
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</code></pre>
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<p>Naive field resolution process would require up to 10 calls to the underlying data store to fetch authors for all 10 stories.</p>
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<p><strong>graphql-php</strong> provides tools to mitigate this problem: it allows you to defer actual field resolution to a later stage
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when one batched query could be executed instead of 10 distinct queries.</p>
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<p>Here is an example of <strong>BlogStory</strong> resolver for field <strong>author</strong> that uses deferring:</p>
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<pre><code class="php"><?php
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'resolve' => function($blogStory) {
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MyUserBuffer::add($blogStory['authorId']);
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return new GraphQL\Deferred(function () use ($blogStory) {
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MyUserBuffer::loadBuffered();
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return MyUserBuffer::get($blogStory['authorId']);
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});
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}
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</code></pre>
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<p>In this example, we fill up the buffer with 10 author ids first. Then <strong>graphql-php</strong> continues
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resolving other non-deferred fields until there are none of them left.</p>
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<p>After that, it calls closures wrapped by <code>GraphQL\Deferred</code> which in turn load all buffered
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ids once (using SQL IN(?), Redis MGET or other similar tools) and returns final field value.</p>
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<p>Originally this approach was advocated by Facebook in their <a href="https://github.com/facebook/dataloader">Dataloader</a>
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project. This solution enables very interesting optimizations at no cost. Consider the following query:</p>
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<pre><code class="graphql">{
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topStories(limit: 10) {
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author {
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email
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}
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}
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category {
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stories(limit: 10) {
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author {
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email
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}
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}
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}
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}
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</code></pre>
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<p>Even though <strong>author</strong> field is located on different levels of the query - it can be buffered in the same buffer.
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In this example, only one query will be executed for all story authors comparing to 20 queries
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in a naive implementation.</p>
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<h1 id="async-php">Async PHP</h1>
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<p>Since: 0.10.0 (version 0.9.0 had slightly different API which still works, but is deprecated)</p>
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<p>If your project runs in an environment that supports async operations
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(like HHVM, ReactPHP, Icicle.io, appserver.io, PHP threads, etc)
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you can leverage the power of your platform to resolve some fields asynchronously.</p>
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<p>The only requirement: your platform must support the concept of Promises compatible with
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<a href="https://promisesaplus.com/">Promises A+</a> specification.</p>
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<p>To start using this feature, switch facade method for query execution from
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<strong>executeQuery</strong> to <strong>promiseToExecute</strong>:</p>
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<pre><code class="php"><?php
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use GraphQL\GraphQL;
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use GraphQL\Executor\ExecutionResult;
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$promise = GraphQL::promiseToExecute(
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$promiseAdapter,
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$schema,
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$queryString,
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$rootValue = null,
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$contextValue = null,
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$variableValues = null,
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$operationName = null,
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$fieldResolver = null,
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$validationRules = null
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);
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$promise->then(function(ExecutionResult $result) {
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return $result->toArray();
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});
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</code></pre>
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<p>Where <strong>$promiseAdapter</strong> is an instance of:</p>
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<ul>
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<li>
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<p>For <a href="https://github.com/reactphp/react">ReactPHP</a> (requires <strong>react/promise</strong> as composer dependency): <br>
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<code>GraphQL\Executor\Promise\Adapter\ReactPromiseAdapter</code></p>
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</li>
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<li>
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<p>Other platforms: write your own class implementing interface: <br>
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<a href="../reference/#graphqlexecutorpromisepromiseadapter"><code>GraphQL\Executor\Promise\PromiseAdapter</code></a>. </p>
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</li>
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</ul>
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<p>Then your <strong>resolve</strong> functions should return promises of your platform instead of <code>GraphQL\Deferred</code>s.</p>
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|
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