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<ol class="chapter"><li class="chapter-item expanded "><a href="../index.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/defining_objects.html"><strong aria-hidden="true">3.1.</strong> Defining 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/using_contexts.html"><strong aria-hidden="true">3.1.2.</strong> Using contexts</a></li><li class="chapter-item expanded "><a href="../types/objects/error_handling.html"><strong aria-hidden="true">3.1.3.</strong> Error handling</a></li></ol></li><li class="chapter-item expanded "><a href="../types/other-index.html"><strong aria-hidden="true">3.2.</strong> Other types</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../types/enums.html"><strong aria-hidden="true">3.2.1.</strong> Enums</a></li><li class="chapter-item expanded "><a href="../types/interfaces.html"><strong aria-hidden="true">3.2.2.</strong> Interfaces</a></li><li class="chapter-item expanded "><a href="../types/input_objects.html"><strong aria-hidden="true">3.2.3.</strong> Input objects</a></li><li class="chapter-item expanded "><a href="../types/scalars.html"><strong aria-hidden="true">3.2.4.</strong> Scalars</a></li><li class="chapter-item expanded "><a href="../types/unions.html" class="active"><strong aria-hidden="true">3.2.5.</strong> Unions</a></li></ol></li></ol></li><li class="chapter-item expanded "><a href="../schema/schemas_and_mutations.html"><strong aria-hidden="true">4.</strong> Schemas and mutations</a></li><li class="chapter-item expanded "><a href="../servers/index.html"><strong aria-hidden="true">5.</strong> Adding A Server</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../servers/official.html"><strong aria-hidden="true">5.1.</strong> Official Server Integrations</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../servers/warp.html"><strong aria-hidden="true">5.1.1.</strong> Warp</a></li><li class="chapter-item expanded "><a href="../servers/rocket.html"><strong aria-hidden="true">5.1.2.</strong> Rocket</a></li><li class="chapter-item expanded "><a href="../servers/iron.html"><strong aria-hidden="true">5.1.3.</strong> Iron</a></li><li class="chapter-item expanded "><a href="../servers/hyper.html"><strong aria-hidden="true">5.1.4.</strong> Hyper</a></li></ol></li><li class="chapter-item expanded "><a href="../servers/third-party.html"><strong aria-hidden="true">5.2.</strong> Third Party Integrations</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/introspection.html"><strong aria-hidden="true">6.1.</strong> Introspection</a></li><li class="chapter-item expanded "><a href="../advanced/non_struct_objects.html"><strong aria-hidden="true">6.2.</strong> Non-struct objects</a></li><li class="chapter-item expanded "><a href="../advanced/implicit_and_explicit_null.html"><strong aria-hidden="true">6.3.</strong> Implicit and explicit null</a></li><li class="chapter-item expanded "><a href="../advanced/objects_and_generics.html"><strong aria-hidden="true">6.4.</strong> Objects and generics</a></li><li class="chapter-item expanded "><a href="../advanced/multiple_ops_per_request.html"><strong aria-hidden="true">6.5.</strong> Multiple operations per request</a></li><li class="chapter-item expanded "><a href="../advanced/dataloaders.html"><strong aria-hidden="true">6.6.</strong> Dataloaders</a></li><li class="chapter-item expanded "><a href="../advanced/subscriptions.html"><strong aria-hidden="true">6.7.</strong> Subscriptions</a></li></ol></li></ol>
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<h1 id="unions"><a class="header" href="#unions">Unions</a></h1>
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<p>From the server's point of view, <a href="https://spec.graphql.org/October2021#sec-Unions">GraphQL unions</a> are somewhat similar to <a href="https://spec.graphql.org/October2021#sec-Interfaces">interfaces</a> - the main difference is that they don't contain fields on their own.</p>
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<p>The most obvious and straightforward way to represent a <a href="https://spec.graphql.org/October2021#sec-Unions">GraphQL union</a> in Rust is enum. However, we also can do so either with trait or a regular struct. That's why, for implementing <a href="https://spec.graphql.org/October2021#sec-Unions">GraphQL unions</a> Juniper provides:</p>
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<ul>
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<li><code>#[derive(GraphQLUnion)]</code> macro for enums and structs.</li>
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<li><code>#[graphql_union]</code> for traits.</li>
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</ul>
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<h2 id="enums"><a class="header" href="#enums">Enums</a></h2>
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<p>Most of the time, we just need a trivial and straightforward Rust enum to represent a <a href="https://spec.graphql.org/October2021#sec-Unions">GraphQL union</a>.</p>
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<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">extern crate juniper;
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</span><span class="boring">extern crate derive_more;
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</span>use derive_more::From;
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use juniper::{GraphQLObject, GraphQLUnion};
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#[derive(GraphQLObject)]
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struct Human {
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id: String,
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home_planet: String,
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}
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#[derive(GraphQLObject)]
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struct Droid {
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id: String,
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primary_function: String,
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}
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#[derive(From, GraphQLUnion)]
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enum Character {
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Human(Human),
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Droid(Droid),
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}
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<span class="boring">
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</span><span class="boring">fn main() {}
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</span></code></pre></pre>
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<h3 id="ignoring-enum-variants"><a class="header" href="#ignoring-enum-variants">Ignoring enum variants</a></h3>
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<p>In some rare situations we may want to omit exposing an enum variant in the GraphQL schema.</p>
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<p>As an example, let's consider the situation where we need to bind some type parameter <code>T</code> for doing interesting type-level stuff in our resolvers. To achieve this we need to have <code>PhantomData<T></code>, but we don't want it exposed in the GraphQL schema.</p>
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<blockquote>
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<p><strong>WARNING</strong>:<br />
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It's the <em>library user's responsibility</em> to ensure that ignored enum variant is <em>never</em> returned from resolvers, otherwise resolving the GraphQL query will <strong>panic at runtime</strong>.</p>
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</blockquote>
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<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">extern crate juniper;
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</span><span class="boring">extern crate derive_more;
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</span><span class="boring">use std::marker::PhantomData;
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</span>use derive_more::From;
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use juniper::{GraphQLObject, GraphQLUnion};
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#[derive(GraphQLObject)]
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struct Human {
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id: String,
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home_planet: String,
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}
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#[derive(GraphQLObject)]
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struct Droid {
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id: String,
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primary_function: String,
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}
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#[derive(From, GraphQLUnion)]
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enum Character<S> {
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Human(Human),
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Droid(Droid),
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#[from(ignore)]
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#[graphql(ignore)] // or `#[graphql(skip)]`, your choice
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_State(PhantomData<S>),
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}
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<span class="boring">
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</span><span class="boring">fn main() {}
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</span></code></pre></pre>
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<h3 id="external-resolver-functions"><a class="header" href="#external-resolver-functions">External resolver functions</a></h3>
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<p>If some custom logic is needed to resolve a <a href="https://spec.graphql.org/October2021#sec-Unions">GraphQL union</a> variant, you may specify an external function to do so:</p>
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<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(dead_code)]
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</span><span class="boring">extern crate juniper;
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</span>use juniper::{GraphQLObject, GraphQLUnion};
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#[derive(GraphQLObject)]
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#[graphql(Context = CustomContext)]
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struct Human {
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id: String,
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home_planet: String,
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}
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#[derive(GraphQLObject)]
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#[graphql(Context = CustomContext)]
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struct Droid {
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id: String,
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primary_function: String,
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}
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pub struct CustomContext {
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droid: Droid,
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}
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impl juniper::Context for CustomContext {}
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#[derive(GraphQLUnion)]
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#[graphql(Context = CustomContext)]
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enum Character {
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Human(Human),
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#[graphql(with = Character::droid_from_context)]
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Droid(Droid),
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}
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impl Character {
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// NOTICE: The function signature must contain `&self` and `&Context`,
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// and return `Option<&VariantType>`.
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fn droid_from_context<'c>(&self, ctx: &'c CustomContext) -> Option<&'c Droid> {
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Some(&ctx.droid)
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}
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}
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<span class="boring">
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</span><span class="boring">fn main() {}
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</span></code></pre></pre>
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<p>With an external resolver function we can even declare a new <a href="https://spec.graphql.org/October2021#sec-Unions">GraphQL union</a> variant where the Rust type is absent in the initial enum definition. The attribute syntax <code>#[graphql(on VariantType = resolver_fn)]</code> follows the <a href="https://spec.graphql.org/October2021#example-f8163">GraphQL syntax for dispatching union variants</a>.</p>
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<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(dead_code)]
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</span><span class="boring">extern crate juniper;
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</span>use juniper::{GraphQLObject, GraphQLUnion};
|
|
|
|
#[derive(GraphQLObject)]
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#[graphql(Context = CustomContext)]
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struct Human {
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id: String,
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home_planet: String,
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}
|
|
|
|
#[derive(GraphQLObject)]
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#[graphql(Context = CustomContext)]
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struct Droid {
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id: String,
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primary_function: String,
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}
|
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|
|
#[derive(GraphQLObject)]
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#[graphql(Context = CustomContext)]
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struct Ewok {
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id: String,
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is_funny: bool,
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}
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pub struct CustomContext {
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ewok: Ewok,
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}
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impl juniper::Context for CustomContext {}
|
|
|
|
#[derive(GraphQLUnion)]
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#[graphql(Context = CustomContext)]
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#[graphql(on Ewok = Character::ewok_from_context)]
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enum Character {
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Human(Human),
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Droid(Droid),
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#[graphql(ignore)] // or `#[graphql(skip)]`, your choice
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Ewok,
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}
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impl Character {
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fn ewok_from_context<'c>(&self, ctx: &'c CustomContext) -> Option<&'c Ewok> {
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if let Self::Ewok = self {
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Some(&ctx.ewok)
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} else {
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None
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}
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}
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}
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<span class="boring">
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</span><span class="boring">fn main() {}
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</span></code></pre></pre>
|
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<h2 id="structs"><a class="header" href="#structs">Structs</a></h2>
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<p>Using Rust structs as <a href="https://spec.graphql.org/October2021#sec-Unions">GraphQL unions</a> is very similar to using enums, with the nuance that specifying an external resolver function is the only way to declare a <a href="https://spec.graphql.org/October2021#sec-Unions">GraphQL union</a> variant.</p>
|
|
<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">extern crate juniper;
|
|
</span><span class="boring">use std::collections::HashMap;
|
|
</span>use juniper::{GraphQLObject, GraphQLUnion};
|
|
|
|
#[derive(GraphQLObject)]
|
|
#[graphql(Context = Database)]
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|
struct Human {
|
|
id: String,
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|
home_planet: String,
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}
|
|
|
|
#[derive(GraphQLObject)]
|
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#[graphql(Context = Database)]
|
|
struct Droid {
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|
id: String,
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primary_function: String,
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}
|
|
|
|
struct Database {
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|
humans: HashMap<String, Human>,
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|
droids: HashMap<String, Droid>,
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}
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impl juniper::Context for Database {}
|
|
|
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#[derive(GraphQLUnion)]
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#[graphql(
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Context = Database,
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on Human = Character::get_human,
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on Droid = Character::get_droid,
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)]
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struct Character {
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|
id: String,
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}
|
|
|
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impl Character {
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fn get_human<'db>(&self, ctx: &'db Database) -> Option<&'db Human>{
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ctx.humans.get(&self.id)
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}
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|
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fn get_droid<'db>(&self, ctx: &'db Database) -> Option<&'db Droid>{
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ctx.droids.get(&self.id)
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}
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}
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<span class="boring">
|
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</span><span class="boring">fn main() {}
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|
</span></code></pre></pre>
|
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<h2 id="traits"><a class="header" href="#traits">Traits</a></h2>
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<p>To use a Rust trait definition as a <a href="https://spec.graphql.org/October2021#sec-Unions">GraphQL union</a> you need to use the <code>#[graphql_union]</code> macro. <a href="https://doc.rust-lang.org/stable/reference/procedural-macros.html#derive-macros">Rust doesn't allow derive macros on traits</a>, so using <code>#[derive(GraphQLUnion)]</code> on traits doesn't work.</p>
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<blockquote>
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<p><strong>NOTICE</strong>:<br />
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A <strong>trait has to be <a href="https://doc.rust-lang.org/stable/reference/items/traits.html#object-safety">object safe</a></strong>, because schema resolvers will need to return a <a href="https://doc.rust-lang.org/stable/reference/types/trait-object.html">trait object</a> to specify a <a href="https://spec.graphql.org/October2021#sec-Unions">GraphQL union</a> behind it.</p>
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</blockquote>
|
|
<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">extern crate juniper;
|
|
</span>use juniper::{graphql_union, GraphQLObject};
|
|
|
|
#[derive(GraphQLObject)]
|
|
struct Human {
|
|
id: String,
|
|
home_planet: String,
|
|
}
|
|
|
|
#[derive(GraphQLObject)]
|
|
struct Droid {
|
|
id: String,
|
|
primary_function: String,
|
|
}
|
|
|
|
#[graphql_union]
|
|
trait Character {
|
|
// NOTICE: The method signature must contain `&self` and return `Option<&VariantType>`.
|
|
fn as_human(&self) -> Option<&Human> { None }
|
|
fn as_droid(&self) -> Option<&Droid> { None }
|
|
}
|
|
|
|
impl Character for Human {
|
|
fn as_human(&self) -> Option<&Human> { Some(&self) }
|
|
}
|
|
|
|
impl Character for Droid {
|
|
fn as_droid(&self) -> Option<&Droid> { Some(&self) }
|
|
}
|
|
<span class="boring">
|
|
</span><span class="boring">fn main() {}
|
|
</span></code></pre></pre>
|
|
<h3 id="custom-context"><a class="header" href="#custom-context">Custom context</a></h3>
|
|
<p>If a <a href="https://docs.rs/juniper/0.14.2/juniper/trait.Context.html"><code>Context</code></a> is required in a trait method to resolve a <a href="https://spec.graphql.org/October2021#sec-Unions">GraphQL union</a> variant, specify it as an argument.</p>
|
|
<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused_variables)]
|
|
</span><span class="boring">extern crate juniper;
|
|
</span><span class="boring">use std::collections::HashMap;
|
|
</span>use juniper::{graphql_union, GraphQLObject};
|
|
|
|
#[derive(GraphQLObject)]
|
|
#[graphql(Context = Database)]
|
|
struct Human {
|
|
id: String,
|
|
home_planet: String,
|
|
}
|
|
|
|
#[derive(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 {}
|
|
|
|
#[graphql_union(context = Database)]
|
|
trait Character {
|
|
// NOTICE: The method signature may optionally contain `&Context`.
|
|
fn as_human<'db>(&self, ctx: &'db Database) -> Option<&'db Human> { None }
|
|
fn as_droid<'db>(&self, ctx: &'db Database) -> Option<&'db Droid> { None }
|
|
}
|
|
|
|
impl Character for Human {
|
|
fn as_human<'db>(&self, ctx: &'db Database) -> Option<&'db Human> {
|
|
ctx.humans.get(&self.id)
|
|
}
|
|
}
|
|
|
|
impl Character for Droid {
|
|
fn as_droid<'db>(&self, ctx: &'db Database) -> Option<&'db Droid> {
|
|
ctx.droids.get(&self.id)
|
|
}
|
|
}
|
|
<span class="boring">
|
|
</span><span class="boring">fn main() {}
|
|
</span></code></pre></pre>
|
|
<h3 id="ignoring-trait-methods"><a class="header" href="#ignoring-trait-methods">Ignoring trait methods</a></h3>
|
|
<p>As with enums, we may want to omit some trait methods to be assumed as <a href="https://spec.graphql.org/October2021#sec-Unions">GraphQL union</a> variants and ignore them.</p>
|
|
<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">extern crate juniper;
|
|
</span>use juniper::{graphql_union, GraphQLObject};
|
|
|
|
#[derive(GraphQLObject)]
|
|
struct Human {
|
|
id: String,
|
|
home_planet: String,
|
|
}
|
|
|
|
#[derive(GraphQLObject)]
|
|
struct Droid {
|
|
id: String,
|
|
primary_function: String,
|
|
}
|
|
|
|
#[graphql_union]
|
|
trait Character {
|
|
fn as_human(&self) -> Option<&Human> { None }
|
|
fn as_droid(&self) -> Option<&Droid> { None }
|
|
#[graphql(ignore)] // or `#[graphql(skip)]`, your choice
|
|
fn id(&self) -> &str;
|
|
}
|
|
|
|
impl Character for Human {
|
|
fn as_human(&self) -> Option<&Human> { Some(&self) }
|
|
fn id(&self) -> &str { self.id.as_str() }
|
|
}
|
|
|
|
impl Character for Droid {
|
|
fn as_droid(&self) -> Option<&Droid> { Some(&self) }
|
|
fn id(&self) -> &str { self.id.as_str() }
|
|
}
|
|
<span class="boring">
|
|
</span><span class="boring">fn main() {}
|
|
</span></code></pre></pre>
|
|
<h3 id="external-resolver-functions-1"><a class="header" href="#external-resolver-functions-1">External resolver functions</a></h3>
|
|
<p>Similarly to enums and structs, it's not mandatory to use trait methods as <a href="https://spec.graphql.org/October2021#sec-Unions">GraphQL union</a> variant resolvers. Instead, custom functions may be specified:</p>
|
|
<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">extern crate juniper;
|
|
</span><span class="boring">use std::collections::HashMap;
|
|
</span>use juniper::{graphql_union, GraphQLObject};
|
|
|
|
#[derive(GraphQLObject)]
|
|
#[graphql(Context = Database)]
|
|
struct Human {
|
|
id: String,
|
|
home_planet: String,
|
|
}
|
|
|
|
#[derive(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 {}
|
|
|
|
#[graphql_union(context = Database)]
|
|
#[graphql_union(
|
|
on Human = DynCharacter::get_human,
|
|
on Droid = get_droid,
|
|
)]
|
|
trait Character {
|
|
#[graphql(ignore)] // or `#[graphql(skip)]`, your choice
|
|
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() }
|
|
}
|
|
|
|
// The trait object is always `Send` and `Sync`.
|
|
type DynCharacter<'a> = dyn Character + Send + Sync + 'a;
|
|
|
|
impl<'a> DynCharacter<'a> {
|
|
fn get_human<'db>(&self, ctx: &'db Database) -> Option<&'db Human> {
|
|
ctx.humans.get(self.id())
|
|
}
|
|
}
|
|
|
|
// External resolver function doesn't have to be a method of a type.
|
|
// It's only a matter of the function signature to match the requirements.
|
|
fn get_droid<'db>(ch: &DynCharacter<'_>, ctx: &'db Database) -> Option<&'db Droid> {
|
|
ctx.droids.get(ch.id())
|
|
}
|
|
<span class="boring">
|
|
</span><span class="boring">fn main() {}
|
|
</span></code></pre></pre>
|
|
<h2 id="scalarvalue-considerations"><a class="header" href="#scalarvalue-considerations"><code>ScalarValue</code> considerations</a></h2>
|
|
<p>By default, <code>#[derive(GraphQLUnion)]</code> and <code>#[graphql_union]</code> macros generate code, which is generic over a <a href="https://docs.rs/juniper/latest/juniper/trait.ScalarValue.html"><code>ScalarValue</code></a> type. This may introduce a problem when at least one of <a href="https://spec.graphql.org/October2021#sec-Unions">GraphQL union</a> variants is restricted to a concrete <a href="https://docs.rs/juniper/latest/juniper/trait.ScalarValue.html"><code>ScalarValue</code></a> type in its implementation. To resolve such problem, a concrete <a href="https://docs.rs/juniper/latest/juniper/trait.ScalarValue.html"><code>ScalarValue</code></a> type should be specified:</p>
|
|
<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(dead_code)]
|
|
</span><span class="boring">extern crate juniper;
|
|
</span>use juniper::{DefaultScalarValue, GraphQLObject, GraphQLUnion};
|
|
|
|
#[derive(GraphQLObject)]
|
|
#[graphql(Scalar = DefaultScalarValue)]
|
|
struct Human {
|
|
id: String,
|
|
home_planet: String,
|
|
}
|
|
|
|
#[derive(GraphQLObject)]
|
|
struct Droid {
|
|
id: String,
|
|
primary_function: String,
|
|
}
|
|
|
|
#[derive(GraphQLUnion)]
|
|
#[graphql(Scalar = DefaultScalarValue)] // removing this line will fail compilation
|
|
enum Character {
|
|
Human(Human),
|
|
Droid(Droid),
|
|
}
|
|
<span class="boring">
|
|
</span><span class="boring">fn main() {}
|
|
</span></code></pre></pre>
|
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