464 lines
22 KiB
HTML
464 lines
22 KiB
HTML
|
<!DOCTYPE HTML>
|
||
|
|
<html lang="en" class="light" dir="ltr">
|
||
|
|
<head>
|
||
|
|
<!-- Book generated using mdBook -->
|
||
|
|
<meta charset="UTF-8">
|
||
|
|
<title>Eager loading - Juniper Book</title>
|
||
|
|
|
||
|
|
|
||
|
|
<!-- Custom HTML head -->
|
||
|
|
|
||
|
|
<meta name="description" content="User guide for Juniper (GraphQL server library for Rust).">
|
||
|
|
<meta name="viewport" content="width=device-width, initial-scale=1">
|
||
|
|
<meta name="theme-color" content="#ffffff">
|
||
|
|
|
||
|
|
<link rel="icon" href="../favicon.svg">
|
||
|
|
<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 rel="stylesheet" href="../fonts/fonts.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="sidebar-visible no-js">
|
||
|
|
<div id="body-container">
|
||
|
|
<!-- Provide site root to javascript -->
|
||
|
|
<script>
|
||
|
|
var path_to_root = "../";
|
||
|
|
var default_theme = window.matchMedia("(prefers-color-scheme: dark)").matches ? "navy" : "light";
|
||
|
|
</script>
|
||
|
|
|
||
|
|
<!-- Work around some values being stored in localStorage wrapped in quotes -->
|
||
|
|
<script>
|
||
|
|
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>
|
||
|
|
var theme;
|
||
|
|
try { theme = localStorage.getItem('mdbook-theme'); } catch(e) { }
|
||
|
|
if (theme === null || theme === undefined) { theme = default_theme; }
|
||
|
|
var html = document.querySelector('html');
|
||
|
|
html.classList.remove('light')
|
||
|
|
html.classList.add(theme);
|
||
|
|
var body = document.querySelector('body');
|
||
|
|
body.classList.remove('no-js')
|
||
|
|
body.classList.add('js');
|
||
|
|
</script>
|
||
|
|
|
||
|
|
<input type="checkbox" id="sidebar-toggle-anchor" class="hidden">
|
||
|
|
|
||
|
|
<!-- Hide / unhide sidebar before it is displayed -->
|
||
|
|
<script>
|
||
|
|
var body = document.querySelector('body');
|
||
|
|
var sidebar = null;
|
||
|
|
var sidebar_toggle = document.getElementById("sidebar-toggle-anchor");
|
||
|
|
if (document.body.clientWidth >= 1080) {
|
||
|
|
try { sidebar = localStorage.getItem('mdbook-sidebar'); } catch(e) { }
|
||
|
|
sidebar = sidebar || 'visible';
|
||
|
|
} else {
|
||
|
|
sidebar = 'hidden';
|
||
|
|
}
|
||
|
|
sidebar_toggle.checked = sidebar === 'visible';
|
||
|
|
body.classList.remove('sidebar-visible');
|
||
|
|
body.classList.add("sidebar-" + sidebar);
|
||
|
|
</script>
|
||
|
|
|
||
|
|
<nav id="sidebar" class="sidebar" aria-label="Table of contents">
|
||
|
|
<div class="sidebar-scrollbox">
|
||
|
|
<ol class="chapter"><li class="chapter-item expanded "><a href="../introduction.html"><strong aria-hidden="true">1.</strong> Introduction</a></li><li class="chapter-item expanded "><a href="../quickstart.html"><strong aria-hidden="true">2.</strong> Quickstart</a></li><li class="chapter-item expanded "><a href="../types/index.html"><strong aria-hidden="true">3.</strong> Type system</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../types/objects/index.html"><strong aria-hidden="true">3.1.</strong> Objects</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../types/objects/complex_fields.html"><strong aria-hidden="true">3.1.1.</strong> Complex fields</a></li><li class="chapter-item expanded "><a href="../types/objects/context.html"><strong aria-hidden="true">3.1.2.</strong> Context</a></li><li class="chapter-item expanded "><a href="../types/objects/error/index.html"><strong aria-hidden="true">3.1.3.</strong> Error handling</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../types/objects/error/field.html"><strong aria-hidden="true">3.1.3.1.</strong> Field errors</a></li><li class="chapter-item expanded "><a href="../types/objects/error/schema.html"><strong aria-hidden="true">3.1.3.2.</strong> Schema errors</a></li></ol></li><li class="chapter-item expanded "><a href="../types/objects/generics.html"><strong aria-hidden="true">3.1.4.</strong> Generics</a></li></ol></li><li class="chapter-item expanded "><a href="../types/interfaces.html"><strong aria-hidden="true">3.2.</strong> Interfaces</a></li><li class="chapter-item expanded "><a href="../types/unions.html"><strong aria-hidden="true">3.3.</strong> Unions</a></li><li class="chapter-item expanded "><a href="../types/enums.html"><strong aria-hidden="true">3.4.</strong> Enums</a></li><li class="chapter-item expanded "><a href="../types/input_objects.html"><strong aria-hidden="true">3.5.</strong> Input objects</a></li><li class="chapter-item expanded "><a href="../types/scalars.html"><strong aria-hidden="true">3.6.</strong> Scalars</a></li></ol></li><li class="chapter-item expanded "><a href="../schema/index.html"><strong aria-hidden="true">4.</strong> Schema</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../schema/subscriptions.html"><strong aria-hidden="true">4.1.</strong> Subscriptions</a></li><li class="chapter-item expanded "><a href="../schema/introspection.html"><strong aria-hidden="true">4.2.</strong> Introspection</a></li></ol></li><li class="chapter-item expanded "><a href="../serve/index.html"><strong aria-hidden="true">5.</strong> Serving</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../serve/batching.html"><strong aria-hidden="true">5.1.</strong> Batching</a></li></ol></li><li class="chapter-item expanded "><a href="../advanced/index.html"><strong aria-hidden="true">6.</strong> Advanced Topics</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../advanced/implicit_and_explicit_null.html"><strong aria-hidden="true">6.1.</strong> Implicit and explicit null</a></li><li class="chapter-item expanded "><a href="../advanced/n_plus_1.html"><strong aria-hidden="true">6.2.</strong> N+1 problem</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../advanced/dataloader.html"><strong aria-hidden="true">6.2.1.</strong> DataLoader</a></li><li class="chapter-item expanded "><a href="../advanced/lookahead.html"><strong aria-hidden="true">6.2.2.</strong> Look-ahead</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../advanced/eager_loading.html" class="active"><strong aria-hidden="true">6.2.2.1.</strong> Eager loading</a></li></ol></li></ol></li></ol></li></ol>
|
||
|
|
</div>
|
||
|
|
<div id="sidebar-resize-handle" class="sidebar-resize-handle">
|
||
|
|
<div class="sidebar-resize-indicator"></div>
|
||
|
|
</div>
|
||
|
|
</nav>
|
||
|
|
|
||
|
|
<!-- Track and set sidebar scroll position -->
|
||
|
|
<script>
|
||
|
|
var sidebarScrollbox = document.querySelector('#sidebar .sidebar-scrollbox');
|
||
|
|
sidebarScrollbox.addEventListener('click', function(e) {
|
||
|
|
if (e.target.tagName === 'A') {
|
||
|
|
sessionStorage.setItem('sidebar-scroll', sidebarScrollbox.scrollTop);
|
||
|
|
}
|
||
|
|
}, { passive: true });
|
||
|
|
var sidebarScrollTop = sessionStorage.getItem('sidebar-scroll');
|
||
|
|
sessionStorage.removeItem('sidebar-scroll');
|
||
|
|
if (sidebarScrollTop) {
|
||
|
|
// preserve sidebar scroll position when navigating via links within sidebar
|
||
|
|
sidebarScrollbox.scrollTop = sidebarScrollTop;
|
||
|
|
} else {
|
||
|
|
// scroll sidebar to current active section when navigating via "next/previous chapter" buttons
|
||
|
|
var activeSection = document.querySelector('#sidebar .active');
|
||
|
|
if (activeSection) {
|
||
|
|
activeSection.scrollIntoView({ block: 'center' });
|
||
|
|
}
|
||
|
|
}
|
||
|
|
</script>
|
||
|
|
|
||
|
|
<div id="page-wrapper" class="page-wrapper">
|
||
|
|
|
||
|
|
<div class="page">
|
||
|
|
<div id="menu-bar-hover-placeholder"></div>
|
||
|
|
<div id="menu-bar" class="menu-bar sticky">
|
||
|
|
<div class="left-buttons">
|
||
|
|
<label id="sidebar-toggle" class="icon-button" for="sidebar-toggle-anchor" title="Toggle Table of Contents" aria-label="Toggle Table of Contents" aria-controls="sidebar">
|
||
|
|
<i class="fa fa-bars"></i>
|
||
|
|
</label>
|
||
|
|
<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</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 Book</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 id="search-wrapper" class="hidden">
|
||
|
|
<form id="searchbar-outer" class="searchbar-outer">
|
||
|
|
<input type="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>
|
||
|
|
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>
|
||
|
|
<h1 id="eager-loading"><a class="header" href="#eager-loading">Eager loading</a></h1>
|
||
|
|
<p>As a further evolution of the <a href="lookahead.html#n1-problem">dealing with the N+1 problem via look-ahead</a>, we may systematically remodel <a href="https://www.rust-lang.org">Rust</a> types mapping to <a href="https://graphql.org">GraphQL</a> ones in the way to encourage doing eager preloading of data for its <a href="https://spec.graphql.org/October2021#sec-Language.Fields">fields</a> and using the already preloaded data when resolving a particular <a href="https://spec.graphql.org/October2021#sec-Language.Fields">field</a>.</p>
|
||
|
|
<p>At the moment, this approach is represented with the <a href="https://docs.rs/juniper-eager-loading"><code>juniper-eager-loading</code></a> crate for <a href="https://docs.rs/juniper">Juniper</a>.</p>
|
||
|
|
<blockquote>
|
||
|
|
<p><strong>NOTE</strong>: Since this library requires <a href="https://docs.rs/juniper-from-schema"><code>juniper-from-schema</code></a>, it's best first to become familiar with it.</p>
|
||
|
|
</blockquote>
|
||
|
|
<!-- TODO: Provide example of solving the problem from "N+1 chapter" once `juniper-eager-loading` support the latest `juniper`. -->
|
||
|
|
<p>From <a href="https://docs.rs/juniper-eager-loading/latest/juniper_eager_loading#how-this-library-works-at-a-high-level">"How this library works at a high level"</a> and <a href="https://docs.rs/juniper-eager-loading/latest/juniper_eager_loading#a-real-example">"A real example"</a> sections of <a href="https://docs.rs/juniper-eager-loading"><code>juniper-eager-loading</code></a> documentation:</p>
|
||
|
|
<blockquote>
|
||
|
|
<h3 id="how-this-library-works-at-a-high-level"><a class="header" href="#how-this-library-works-at-a-high-level">How this library works at a high level</a></h3>
|
||
|
|
<p>If you have a GraphQL type like this</p>
|
||
|
|
<pre><code class="language-graphql">type User {
|
||
|
|
id: Int!
|
||
|
|
country: Country!
|
||
|
|
}
|
||
|
|
</code></pre>
|
||
|
|
<p>You might create the corresponding Rust model type like this:</p>
|
||
|
|
<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
|
||
|
|
</span><span class="boring">fn main() {
|
||
|
|
</span>struct User {
|
||
|
|
id: i32,
|
||
|
|
country_id: i32,
|
||
|
|
}
|
||
|
|
<span class="boring">}</span></code></pre></pre>
|
||
|
|
<p>However this approach has one big issue. How are you going to resolve the field <code>User.country</code>
|
||
|
|
without doing a database query? All the resolver has access to is a <code>User</code> with a <code>country_id</code>
|
||
|
|
field. It can't get the country without loading it from the database...</p>
|
||
|
|
<p>Fundamentally these kinds of model structs don't work for eager loading with GraphQL. So
|
||
|
|
this library takes a different approach.</p>
|
||
|
|
<p>What if we created separate structs for the database models and the GraphQL models? Something
|
||
|
|
like this:</p>
|
||
|
|
<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">fn main() {}
|
||
|
|
</span><span class="boring">
|
||
|
|
</span>mod models {
|
||
|
|
pub struct User {
|
||
|
|
id: i32,
|
||
|
|
country_id: i32
|
||
|
|
}
|
||
|
|
|
||
|
|
pub struct Country {
|
||
|
|
id: i32,
|
||
|
|
}
|
||
|
|
}
|
||
|
|
|
||
|
|
struct User {
|
||
|
|
user: models::User,
|
||
|
|
country: HasOne<Country>,
|
||
|
|
}
|
||
|
|
|
||
|
|
struct Country {
|
||
|
|
country: models::Country
|
||
|
|
}
|
||
|
|
|
||
|
|
enum HasOne<T> {
|
||
|
|
Loaded(T),
|
||
|
|
NotLoaded,
|
||
|
|
}</code></pre></pre>
|
||
|
|
<p>Now we're able to resolve the query with code like this:</p>
|
||
|
|
<ol>
|
||
|
|
<li>Load all the users (first query).</li>
|
||
|
|
<li>Map the users to a list of country ids.</li>
|
||
|
|
<li>Load all the countries with those ids (second query).</li>
|
||
|
|
<li>Pair up the users with the country with the correct id, so change <code>User.country</code> from
|
||
|
|
<code>HasOne::NotLoaded</code> to <code>HasOne::Loaded(matching_country)</code>.</li>
|
||
|
|
<li>When resolving the GraphQL field <code>User.country</code> simply return the loaded country.</li>
|
||
|
|
</ol>
|
||
|
|
<h3 id="a-real-example"><a class="header" href="#a-real-example">A real example</a></h3>
|
||
|
|
<pre><code class="language-rust ignore">use juniper::{Executor, FieldResult};
|
||
|
|
use juniper_eager_loading::{prelude::*, EagerLoading, HasOne};
|
||
|
|
use juniper_from_schema::graphql_schema;
|
||
|
|
use std::error::Error;
|
||
|
|
|
||
|
|
// Define our GraphQL schema.
|
||
|
|
graphql_schema! {
|
||
|
|
schema {
|
||
|
|
query: Query
|
||
|
|
}
|
||
|
|
|
||
|
|
type Query {
|
||
|
|
allUsers: [User!]! @juniper(ownership: "owned")
|
||
|
|
}
|
||
|
|
|
||
|
|
type User {
|
||
|
|
id: Int!
|
||
|
|
country: Country!
|
||
|
|
}
|
||
|
|
|
||
|
|
type Country {
|
||
|
|
id: Int!
|
||
|
|
}
|
||
|
|
}
|
||
|
|
|
||
|
|
// Our model types.
|
||
|
|
mod models {
|
||
|
|
use std::error::Error;
|
||
|
|
use juniper_eager_loading::LoadFrom;
|
||
|
|
|
||
|
|
#[derive(Clone)]
|
||
|
|
pub struct User {
|
||
|
|
pub id: i32,
|
||
|
|
pub country_id: i32
|
||
|
|
}
|
||
|
|
|
||
|
|
#[derive(Clone)]
|
||
|
|
pub struct Country {
|
||
|
|
pub id: i32,
|
||
|
|
}
|
||
|
|
|
||
|
|
// This trait is required for eager loading countries.
|
||
|
|
// It defines how to load a list of countries from a list of ids.
|
||
|
|
// Notice that `Context` is generic and can be whatever you want.
|
||
|
|
// It will normally be your Juniper context which would contain
|
||
|
|
// a database connection.
|
||
|
|
impl LoadFrom<i32> for Country {
|
||
|
|
type Error = Box<dyn Error>;
|
||
|
|
type Context = super::Context;
|
||
|
|
|
||
|
|
fn load(
|
||
|
|
employments: &[i32],
|
||
|
|
field_args: &(),
|
||
|
|
ctx: &Self::Context,
|
||
|
|
) -> Result<Vec<Self>, Self::Error> {
|
||
|
|
// ...
|
||
|
|
<span class="boring"> unimplemented!()
|
||
|
|
</span> }
|
||
|
|
}
|
||
|
|
}
|
||
|
|
|
||
|
|
// Our sample database connection type.
|
||
|
|
pub struct DbConnection;
|
||
|
|
|
||
|
|
impl DbConnection {
|
||
|
|
// Function that will load all the users.
|
||
|
|
fn load_all_users(&self) -> Vec<models::User> {
|
||
|
|
// ...
|
||
|
|
<span class="boring"> unimplemented!()
|
||
|
|
</span> }
|
||
|
|
}
|
||
|
|
|
||
|
|
// Our Juniper context type which contains a database connection.
|
||
|
|
pub struct Context {
|
||
|
|
db: DbConnection,
|
||
|
|
}
|
||
|
|
|
||
|
|
impl juniper::Context for Context {}
|
||
|
|
|
||
|
|
// Our GraphQL user type.
|
||
|
|
// `#[derive(EagerLoading)]` takes care of generating all the boilerplate code.
|
||
|
|
#[derive(Clone, EagerLoading)]
|
||
|
|
// You need to set the context and error type.
|
||
|
|
#[eager_loading(
|
||
|
|
context = Context,
|
||
|
|
error = Box<dyn Error>,
|
||
|
|
|
||
|
|
// These match the default so you wouldn't have to specify them
|
||
|
|
model = models::User,
|
||
|
|
id = i32,
|
||
|
|
root_model_field = user,
|
||
|
|
)]
|
||
|
|
pub struct User {
|
||
|
|
// This user model is used to resolve `User.id`
|
||
|
|
user: models::User,
|
||
|
|
|
||
|
|
// Setup a "has one" association between a user and a country.
|
||
|
|
//
|
||
|
|
// We could also have used `#[has_one(default)]` here.
|
||
|
|
#[has_one(
|
||
|
|
foreign_key_field = country_id,
|
||
|
|
root_model_field = country,
|
||
|
|
graphql_field = country,
|
||
|
|
)]
|
||
|
|
country: HasOne<Country>,
|
||
|
|
}
|
||
|
|
|
||
|
|
// And the GraphQL country type.
|
||
|
|
#[derive(Clone, EagerLoading)]
|
||
|
|
#[eager_loading(context = Context, error = Box<dyn Error>)]
|
||
|
|
pub struct Country {
|
||
|
|
country: models::Country,
|
||
|
|
}
|
||
|
|
|
||
|
|
// The root query GraphQL type.
|
||
|
|
pub struct Query;
|
||
|
|
|
||
|
|
impl QueryFields for Query {
|
||
|
|
// The resolver for `Query.allUsers`.
|
||
|
|
fn field_all_users(
|
||
|
|
&self,
|
||
|
|
executor: &Executor<'_, Context>,
|
||
|
|
trail: &QueryTrail<'_, User, Walked>,
|
||
|
|
) -> FieldResult<Vec<User>> {
|
||
|
|
let ctx = executor.context();
|
||
|
|
|
||
|
|
// Load the model users.
|
||
|
|
let user_models = ctx.db.load_all_users();
|
||
|
|
|
||
|
|
// Turn the model users into GraphQL users.
|
||
|
|
let mut users = User::from_db_models(&user_models);
|
||
|
|
|
||
|
|
// Perform the eager loading.
|
||
|
|
// `trail` is used to only eager load the fields that are requested. Because
|
||
|
|
// we're using `QueryTrail`s from "juniper_from_schema" it would be a compile
|
||
|
|
// error if we eager loaded associations that aren't requested in the query.
|
||
|
|
User::eager_load_all_children_for_each(&mut users, &user_models, ctx, trail)?;
|
||
|
|
|
||
|
|
Ok(users)
|
||
|
|
}
|
||
|
|
}
|
||
|
|
|
||
|
|
impl UserFields for User {
|
||
|
|
fn field_id(
|
||
|
|
&self,
|
||
|
|
executor: &Executor<'_, Context>,
|
||
|
|
) -> FieldResult<&i32> {
|
||
|
|
Ok(&self.user.id)
|
||
|
|
}
|
||
|
|
|
||
|
|
fn field_country(
|
||
|
|
&self,
|
||
|
|
executor: &Executor<'_, Context>,
|
||
|
|
trail: &QueryTrail<'_, Country, Walked>,
|
||
|
|
) -> FieldResult<&Country> {
|
||
|
|
// This will unwrap the country from the `HasOne` or return an error if the
|
||
|
|
// country wasn't loaded, or wasn't found in the database.
|
||
|
|
Ok(self.country.try_unwrap()?)
|
||
|
|
}
|
||
|
|
}
|
||
|
|
|
||
|
|
impl CountryFields for Country {
|
||
|
|
fn field_id(
|
||
|
|
&self,
|
||
|
|
executor: &Executor<'_, Context>,
|
||
|
|
) -> FieldResult<&i32> {
|
||
|
|
Ok(&self.country.id)
|
||
|
|
}
|
||
|
|
}
|
||
|
|
<span class="boring">
|
||
|
|
</span><span class="boring">fn main() {}</span></code></pre>
|
||
|
|
</blockquote>
|
||
|
|
<p>For more details, check out the <a href="https://docs.rs/juniper-eager-loading"><code>juniper-eager-loading</code> documentation</a>.</p>
|
||
|
|
<h2 id="full-example"><a class="header" href="#full-example">Full example</a></h2>
|
||
|
|
<p>For a full example using eager loading in <a href="https://docs.rs/juniper">Juniper</a> check out the <a href="https://github.com/davidpdrsn/graphql-app-example"><code>davidpdrsn/graphql-app-example</code> repository</a>.</p>
|
||
|
|
|
||
|
|
</main>
|
||
|
|
|
||
|
|
<nav class="nav-wrapper" aria-label="Page navigation">
|
||
|
|
<!-- Mobile navigation buttons -->
|
||
|
|
<a rel="prev" href="../advanced/lookahead.html" class="mobile-nav-chapters previous" title="Previous chapter" aria-label="Previous chapter" aria-keyshortcuts="Left">
|
||
|
|
<i class="fa fa-angle-left"></i>
|
||
|
|
</a>
|
||
|
|
|
||
|
|
|
||
|
|
<div style="clear: both"></div>
|
||
|
|
</nav>
|
||
|
|
</div>
|
||
|
|
</div>
|
||
|
|
|
||
|
|
<nav class="nav-wide-wrapper" aria-label="Page navigation">
|
||
|
|
<a rel="prev" href="../advanced/lookahead.html" class="nav-chapters previous" title="Previous chapter" aria-label="Previous chapter" aria-keyshortcuts="Left">
|
||
|
|
<i class="fa fa-angle-left"></i>
|
||
|
|
</a>
|
||
|
|
|
||
|
|
</nav>
|
||
|
|
|
||
|
|
</div>
|
||
|
|
|
||
|
|
|
||
|
|
|
||
|
|
|
||
|
|
<script>
|
||
|
|
window.playground_copyable = true;
|
||
|
|
</script>
|
||
|
|
|
||
|
|
|
||
|
|
<script src="../elasticlunr.min.js"></script>
|
||
|
|
<script src="../mark.min.js"></script>
|
||
|
|
<script src="../searcher.js"></script>
|
||
|
|
|
||
|
|
<script src="../clipboard.min.js"></script>
|
||
|
|
<script src="../highlight.js"></script>
|
||
|
|
<script src="../book.js"></script>
|
||
|
|
|
||
|
|
<!-- Custom JS scripts -->
|
||
|
|
|
||
|
|
|
||
|
|
</div>
|
||
|
|
</body>
|
||
|
|
</html>
|