391 lines
19 KiB
HTML
391 lines
19 KiB
HTML
<!DOCTYPE HTML>
|
|
<html lang="en" class="sidebar-visible no-js">
|
|
<head>
|
|
<!-- Book generated using mdBook -->
|
|
<meta charset="UTF-8">
|
|
<title>Interfaces - Juniper - GraphQL Server for Rust</title>
|
|
<meta content="text/html; charset=utf-8" http-equiv="Content-Type">
|
|
<meta name="description" content="Documentation for juniper, a GraphQL server library for Rust.">
|
|
<meta name="viewport" content="width=device-width, initial-scale=1">
|
|
<meta name="theme-color" content="#ffffff" />
|
|
|
|
<link rel="shortcut icon" href="../favicon.png">
|
|
<link rel="stylesheet" href="../css/variables.css">
|
|
<link rel="stylesheet" href="../css/general.css">
|
|
<link rel="stylesheet" href="../css/chrome.css">
|
|
<link rel="stylesheet" href="../css/print.css" media="print">
|
|
|
|
<!-- Fonts -->
|
|
<link rel="stylesheet" href="../FontAwesome/css/font-awesome.css">
|
|
<link href="https://fonts.googleapis.com/css?family=Open+Sans:300italic,400italic,600italic,700italic,800italic,400,300,600,700,800" rel="stylesheet" type="text/css">
|
|
<link href="https://fonts.googleapis.com/css?family=Source+Code+Pro:500" rel="stylesheet" type="text/css">
|
|
|
|
<!-- Highlight.js Stylesheets -->
|
|
<link rel="stylesheet" href="../highlight.css">
|
|
<link rel="stylesheet" href="../tomorrow-night.css">
|
|
<link rel="stylesheet" href="../ayu-highlight.css">
|
|
|
|
<!-- Custom theme stylesheets -->
|
|
|
|
|
|
|
|
</head>
|
|
<body class="light">
|
|
<!-- Provide site root to javascript -->
|
|
<script type="text/javascript">var path_to_root = "../";</script>
|
|
|
|
<!-- Work around some values being stored in localStorage wrapped in quotes -->
|
|
<script type="text/javascript">
|
|
try {
|
|
var theme = localStorage.getItem('mdbook-theme');
|
|
var sidebar = localStorage.getItem('mdbook-sidebar');
|
|
|
|
if (theme.startsWith('"') && theme.endsWith('"')) {
|
|
localStorage.setItem('mdbook-theme', theme.slice(1, theme.length - 1));
|
|
}
|
|
|
|
if (sidebar.startsWith('"') && sidebar.endsWith('"')) {
|
|
localStorage.setItem('mdbook-sidebar', sidebar.slice(1, sidebar.length - 1));
|
|
}
|
|
} catch (e) { }
|
|
</script>
|
|
|
|
<!-- Set the theme before any content is loaded, prevents flash -->
|
|
<script type="text/javascript">
|
|
var theme;
|
|
try { theme = localStorage.getItem('mdbook-theme'); } catch(e) { }
|
|
if (theme === null || theme === undefined) { theme = 'light'; }
|
|
document.body.className = theme;
|
|
document.querySelector('html').className = theme + ' js';
|
|
</script>
|
|
|
|
<!-- Hide / unhide sidebar before it is displayed -->
|
|
<script type="text/javascript">
|
|
var html = document.querySelector('html');
|
|
var sidebar = 'hidden';
|
|
if (document.body.clientWidth >= 1080) {
|
|
try { sidebar = localStorage.getItem('mdbook-sidebar'); } catch(e) { }
|
|
sidebar = sidebar || 'visible';
|
|
}
|
|
html.classList.remove('sidebar-visible');
|
|
html.classList.add("sidebar-" + sidebar);
|
|
</script>
|
|
|
|
<nav id="sidebar" class="sidebar" aria-label="Table of contents">
|
|
<ol class="chapter"><li class="affix"><a href="../index.html">Introduction</a></li><li class="affix"><a href="../quickstart.html">Quickstart</a></li><li class="affix"><a href="../types/index.html">Type System</a></li><li><a href="../types/objects/defining_objects.html"><strong aria-hidden="true">1.</strong> Defining objects</a></li><li><ol class="section"><li><a href="../types/objects/complex_fields.html"><strong aria-hidden="true">1.1.</strong> Complex fields</a></li><li><a href="../types/objects/using_contexts.html"><strong aria-hidden="true">1.2.</strong> Using contexts</a></li><li><a href="../types/objects/error_handling.html"><strong aria-hidden="true">1.3.</strong> Error handling</a></li></ol></li><li><a href="../types/other-index.html"><strong aria-hidden="true">2.</strong> Other types</a></li><li><ol class="section"><li><a href="../types/enums.html"><strong aria-hidden="true">2.1.</strong> Enums</a></li><li><a href="../types/interfaces.html" class="active"><strong aria-hidden="true">2.2.</strong> Interfaces</a></li><li><a href="../types/input_objects.html"><strong aria-hidden="true">2.3.</strong> Input objects</a></li><li><a href="../types/scalars.html"><strong aria-hidden="true">2.4.</strong> Scalars</a></li><li><a href="../types/unions.html"><strong aria-hidden="true">2.5.</strong> Unions</a></li></ol></li><li><a href="../schema/schemas_and_mutations.html"><strong aria-hidden="true">3.</strong> Schemas and mutations</a></li><li><a href="../servers/index.html"><strong aria-hidden="true">4.</strong> Adding A Server</a></li><li><ol class="section"><li><a href="../servers/official.html"><strong aria-hidden="true">4.1.</strong> Official Server Integrations</a></li><li><ol class="section"><li><a href="../servers/warp.html"><strong aria-hidden="true">4.1.1.</strong> Warp</a></li><li><a href="../servers/rocket.html"><strong aria-hidden="true">4.1.2.</strong> Rocket</a></li><li><a href="../servers/iron.html"><strong aria-hidden="true">4.1.3.</strong> Iron</a></li><li><a href="../servers/hyper.html"><strong aria-hidden="true">4.1.4.</strong> Hyper</a></li></ol></li><li><a href="../servers/third-party.html"><strong aria-hidden="true">4.2.</strong> Third Party Integrations</a></li></ol></li><li><a href="../advanced/index.html"><strong aria-hidden="true">5.</strong> Advanced Topics</a></li><li><ol class="section"><li><a href="../advanced/introspection.html"><strong aria-hidden="true">5.1.</strong> Introspection</a></li><li><a href="../advanced/non_struct_objects.html"><strong aria-hidden="true">5.2.</strong> Non-struct objects</a></li><li><a href="../advanced/objects_and_generics.html"><strong aria-hidden="true">5.3.</strong> Objects and generics</a></li><li><a href="../advanced/multiple_ops_per_request.html"><strong aria-hidden="true">5.4.</strong> Multiple operations per request</a></li><li><a href="../advanced/dataloaders.html"><strong aria-hidden="true">5.5.</strong> Dataloaders</a></li></ol></li></ol>
|
|
</nav>
|
|
|
|
<div id="page-wrapper" class="page-wrapper">
|
|
|
|
<div class="page">
|
|
|
|
<div id="menu-bar" class="menu-bar">
|
|
<div id="menu-bar-sticky-container">
|
|
<div class="left-buttons">
|
|
<button id="sidebar-toggle" class="icon-button" type="button" title="Toggle Table of Contents" aria-label="Toggle Table of Contents" aria-controls="sidebar">
|
|
<i class="fa fa-bars"></i>
|
|
</button>
|
|
<button id="theme-toggle" class="icon-button" type="button" title="Change theme" aria-label="Change theme" aria-haspopup="true" aria-expanded="false" aria-controls="theme-list">
|
|
<i class="fa fa-paint-brush"></i>
|
|
</button>
|
|
<ul id="theme-list" class="theme-popup" aria-label="Themes" role="menu">
|
|
<li role="none"><button role="menuitem" class="theme" id="light">Light <span class="default">(default)</span></button></li>
|
|
<li role="none"><button role="menuitem" class="theme" id="rust">Rust</button></li>
|
|
<li role="none"><button role="menuitem" class="theme" id="coal">Coal</button></li>
|
|
<li role="none"><button role="menuitem" class="theme" id="navy">Navy</button></li>
|
|
<li role="none"><button role="menuitem" class="theme" id="ayu">Ayu</button></li>
|
|
</ul>
|
|
|
|
<button id="search-toggle" class="icon-button" type="button" title="Search. (Shortkey: s)" aria-label="Toggle Searchbar" aria-expanded="false" aria-keyshortcuts="S" aria-controls="searchbar">
|
|
<i class="fa fa-search"></i>
|
|
</button>
|
|
|
|
</div>
|
|
|
|
<h1 class="menu-title">Juniper - GraphQL Server for Rust</h1>
|
|
|
|
<div class="right-buttons">
|
|
<a href="../print.html" title="Print this book" aria-label="Print this book">
|
|
<i id="print-button" class="fa fa-print"></i>
|
|
</a>
|
|
</div>
|
|
</div>
|
|
</div>
|
|
|
|
|
|
<div id="search-wrapper" class="hidden">
|
|
<form id="searchbar-outer" class="searchbar-outer">
|
|
<input type="search" name="search" id="searchbar" name="searchbar" placeholder="Search this book ..." aria-controls="searchresults-outer" aria-describedby="searchresults-header">
|
|
</form>
|
|
<div id="searchresults-outer" class="searchresults-outer hidden">
|
|
<div id="searchresults-header" class="searchresults-header"></div>
|
|
<ul id="searchresults">
|
|
</ul>
|
|
</div>
|
|
</div>
|
|
|
|
|
|
<!-- Apply ARIA attributes after the sidebar and the sidebar toggle button are added to the DOM -->
|
|
<script type="text/javascript">
|
|
document.getElementById('sidebar-toggle').setAttribute('aria-expanded', sidebar === 'visible');
|
|
document.getElementById('sidebar').setAttribute('aria-hidden', sidebar !== 'visible');
|
|
Array.from(document.querySelectorAll('#sidebar a')).forEach(function(link) {
|
|
link.setAttribute('tabIndex', sidebar === 'visible' ? 0 : -1);
|
|
});
|
|
</script>
|
|
|
|
<div id="content" class="content">
|
|
<main>
|
|
<a class="header" href="#interfaces" id="interfaces"><h1>Interfaces</h1></a>
|
|
<p>GraphQL interfaces map well to interfaces known from common object-oriented
|
|
languages such as Java or C#, but Rust has unfortunately not a concept that maps
|
|
perfectly to them. Because of this, defining interfaces in Juniper can require a
|
|
little bit of boilerplate code, but on the other hand gives you full control
|
|
over which type is backing your interface.</p>
|
|
<p>To highlight a couple of different ways you can implement interfaces in Rust,
|
|
let's have a look at the same end-result from a few different implementations:</p>
|
|
<a class="header" href="#traits" id="traits"><h2>Traits</h2></a>
|
|
<p>Traits are maybe the most obvious concept you want to use when building
|
|
interfaces. But because GraphQL supports downcasting while Rust doesn't, you'll
|
|
have to manually specify how to convert a trait into a concrete type. This can
|
|
be done in a couple of different ways:</p>
|
|
<a class="header" href="#downcasting-via-accessor-methods" id="downcasting-via-accessor-methods"><h3>Downcasting via accessor methods</h3></a>
|
|
<pre><code class="language-rust ignore">#[derive(juniper::GraphQLObject)]
|
|
struct Human {
|
|
id: String,
|
|
home_planet: String,
|
|
}
|
|
|
|
#[derive(juniper::GraphQLObject)]
|
|
struct Droid {
|
|
id: String,
|
|
primary_function: String,
|
|
}
|
|
|
|
trait Character {
|
|
fn id(&self) -> &str;
|
|
|
|
// Downcast methods, each concrete class will need to implement one of these
|
|
fn as_human(&self) -> Option<&Human> { None }
|
|
fn as_droid(&self) -> Option<&Droid> { None }
|
|
}
|
|
|
|
impl Character for Human {
|
|
fn id(&self) -> &str { self.id.as_str() }
|
|
fn as_human(&self) -> Option<&Human> { Some(&self) }
|
|
}
|
|
|
|
impl Character for Droid {
|
|
fn id(&self) -> &str { self.id.as_str() }
|
|
fn as_droid(&self) -> Option<&Droid> { Some(&self) }
|
|
}
|
|
|
|
juniper::graphql_interface!(<'a> &'a dyn Character: () as "Character" where Scalar = <S> |&self| {
|
|
field id() -> &str { self.id() }
|
|
|
|
instance_resolvers: |_| {
|
|
// The left hand side indicates the concrete type T, the right hand
|
|
// side should be an expression returning Option<T>
|
|
&Human => self.as_human(),
|
|
&Droid => self.as_droid(),
|
|
}
|
|
});
|
|
|
|
# fn main() {}
|
|
</code></pre>
|
|
<p>The <code>instance_resolvers</code> declaration lists all the implementors of the given
|
|
interface and how to resolve them.</p>
|
|
<p>As you can see, you lose a bit of the point with using traits: you need to list
|
|
all the concrete types in the trait itself, and there's a bit of repetition
|
|
going on.</p>
|
|
<a class="header" href="#using-an-extra-database-lookup" id="using-an-extra-database-lookup"><h3>Using an extra database lookup</h3></a>
|
|
<p>If you can afford an extra database lookup when the concrete class is requested,
|
|
you can do away with the downcast methods and use the context instead. Here,
|
|
we'll use two hashmaps, but this could be two tables and some SQL calls instead:</p>
|
|
<pre><code class="language-rust ignore"># use std::collections::HashMap;
|
|
#[derive(juniper::GraphQLObject)]
|
|
#[graphql(Context = Database)]
|
|
struct Human {
|
|
id: String,
|
|
home_planet: String,
|
|
}
|
|
|
|
#[derive(juniper::GraphQLObject)]
|
|
#[graphql(Context = Database)]
|
|
struct Droid {
|
|
id: String,
|
|
primary_function: String,
|
|
}
|
|
|
|
struct Database {
|
|
humans: HashMap<String, Human>,
|
|
droids: HashMap<String, Droid>,
|
|
}
|
|
|
|
impl juniper::Context for Database {}
|
|
|
|
trait Character {
|
|
fn id(&self) -> &str;
|
|
}
|
|
|
|
impl Character for Human {
|
|
fn id(&self) -> &str { self.id.as_str() }
|
|
}
|
|
|
|
impl Character for Droid {
|
|
fn id(&self) -> &str { self.id.as_str() }
|
|
}
|
|
|
|
juniper::graphql_interface!(<'a> &'a dyn Character: Database as "Character" where Scalar = <S> |&self| {
|
|
field id() -> &str { self.id() }
|
|
|
|
instance_resolvers: |&context| {
|
|
&Human => context.humans.get(self.id()),
|
|
&Droid => context.droids.get(self.id()),
|
|
}
|
|
});
|
|
|
|
# fn main() {}
|
|
</code></pre>
|
|
<p>This removes the need of downcast methods, but still requires some repetition.</p>
|
|
<a class="header" href="#placeholder-objects" id="placeholder-objects"><h2>Placeholder objects</h2></a>
|
|
<p>Continuing on from the last example, the trait itself seems a bit unneccesary.
|
|
Maybe it can just be a struct containing the ID?</p>
|
|
<pre><code class="language-rust ignore"># use std::collections::HashMap;
|
|
#[derive(juniper::GraphQLObject)]
|
|
#[graphql(Context = "Database")]
|
|
struct Human {
|
|
id: String,
|
|
home_planet: String,
|
|
}
|
|
|
|
#[derive(juniper::GraphQLObject)]
|
|
#[graphql(Context = "Database")]
|
|
struct Droid {
|
|
id: String,
|
|
primary_function: String,
|
|
}
|
|
|
|
struct Database {
|
|
humans: HashMap<String, Human>,
|
|
droids: HashMap<String, Droid>,
|
|
}
|
|
|
|
impl juniper::Context for Database {}
|
|
|
|
struct Character {
|
|
id: String,
|
|
}
|
|
|
|
juniper::graphql_interface!(Character: Database where Scalar = <S> |&self| {
|
|
field id() -> &str { self.id.as_str() }
|
|
|
|
instance_resolvers: |&context| {
|
|
&Human => context.humans.get(&self.id),
|
|
&Droid => context.droids.get(&self.id),
|
|
}
|
|
});
|
|
|
|
# fn main() {}
|
|
</code></pre>
|
|
<p>This reduces repetition some more, but might be impractical if the interface's
|
|
surface area is large.</p>
|
|
<a class="header" href="#enums" id="enums"><h2>Enums</h2></a>
|
|
<p>Using enums and pattern matching lies half-way between using traits and using
|
|
placeholder objects. We don't need the extra database call in this case, so
|
|
we'll remove it.</p>
|
|
<pre><code class="language-rust ignore">#[derive(juniper::GraphQLObject)]
|
|
struct Human {
|
|
id: String,
|
|
home_planet: String,
|
|
}
|
|
|
|
#[derive(juniper::GraphQLObject)]
|
|
struct Droid {
|
|
id: String,
|
|
primary_function: String,
|
|
}
|
|
|
|
# #[allow(dead_code)]
|
|
enum Character {
|
|
Human(Human),
|
|
Droid(Droid),
|
|
}
|
|
|
|
juniper::graphql_interface!(Character: () where Scalar = <S> |&self| {
|
|
field id() -> &str {
|
|
match *self {
|
|
Character::Human(Human { ref id, .. }) |
|
|
Character::Droid(Droid { ref id, .. }) => id,
|
|
}
|
|
}
|
|
|
|
instance_resolvers: |_| {
|
|
&Human => match *self { Character::Human(ref h) => Some(h), _ => None },
|
|
&Droid => match *self { Character::Droid(ref d) => Some(d), _ => None },
|
|
}
|
|
});
|
|
|
|
# fn main() {}
|
|
</code></pre>
|
|
|
|
</main>
|
|
|
|
<nav class="nav-wrapper" aria-label="Page navigation">
|
|
<!-- Mobile navigation buttons -->
|
|
|
|
<a rel="prev" href="../types/enums.html" class="mobile-nav-chapters previous" title="Previous chapter" aria-label="Previous chapter" aria-keyshortcuts="Left">
|
|
<i class="fa fa-angle-left"></i>
|
|
</a>
|
|
|
|
|
|
|
|
<a rel="next" href="../types/input_objects.html" class="mobile-nav-chapters next" title="Next chapter" aria-label="Next chapter" aria-keyshortcuts="Right">
|
|
<i class="fa fa-angle-right"></i>
|
|
</a>
|
|
|
|
|
|
<div style="clear: both"></div>
|
|
</nav>
|
|
</div>
|
|
</div>
|
|
|
|
<nav class="nav-wide-wrapper" aria-label="Page navigation">
|
|
|
|
<a href="../types/enums.html" class="nav-chapters previous" title="Previous chapter" aria-label="Previous chapter" aria-keyshortcuts="Left">
|
|
<i class="fa fa-angle-left"></i>
|
|
</a>
|
|
|
|
|
|
|
|
<a href="../types/input_objects.html" class="nav-chapters next" title="Next chapter" aria-label="Next chapter" aria-keyshortcuts="Right">
|
|
<i class="fa fa-angle-right"></i>
|
|
</a>
|
|
|
|
</nav>
|
|
|
|
</div>
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
<script src="../elasticlunr.min.js" type="text/javascript" charset="utf-8"></script>
|
|
<script src="../mark.min.js" type="text/javascript" charset="utf-8"></script>
|
|
<script src="../searcher.js" type="text/javascript" charset="utf-8"></script>
|
|
|
|
|
|
<script src="../clipboard.min.js" type="text/javascript" charset="utf-8"></script>
|
|
<script src="../highlight.js" type="text/javascript" charset="utf-8"></script>
|
|
<script src="../book.js" type="text/javascript" charset="utf-8"></script>
|
|
|
|
<!-- Custom JS scripts -->
|
|
|
|
|
|
|
|
|
|
</body>
|
|
</html>
|