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<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"><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" class="active"><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/implicit_and_explicit_null.html"><strong aria-hidden="true">5.3.</strong> Implicit and explicit null</a></li><li><a href="../advanced/objects_and_generics.html"><strong aria-hidden="true">5.4.</strong> Objects and generics</a></li><li><a href="../advanced/multiple_ops_per_request.html"><strong aria-hidden="true">5.5.</strong> Multiple operations per request</a></li><li><a href="../advanced/dataloaders.html"><strong aria-hidden="true">5.6.</strong> Dataloaders</a></li><li><a href="../advanced/subscriptions.html"><strong aria-hidden="true">5.7.</strong> Subscriptions</a></li></ol></li></ol>
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<h1 class="menu-title">Juniper - GraphQL Server for Rust</h1>
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<a class="header" href="#scalars" id="scalars"><h1>Scalars</h1></a>
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<p>Scalars are the primitive types at the leaves of a GraphQL query: numbers,
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strings, and booleans. You can create custom scalars to other primitive values,
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but this often requires coordination with the client library intended to consume
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the API you're building.</p>
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<p>Since any value going over the wire is eventually transformed into JSON, you're
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also limited in the data types you can use.</p>
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<p>There are two ways to define custom scalars.</p>
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<ul>
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<li>For simple scalars that just wrap a primitive type, you can use the newtype pattern with
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a custom derive.</li>
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<li>For more advanced use cases with custom validation, you can use
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the <code>graphql_scalar</code> proc macro.</li>
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</ul>
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<a class="header" href="#built-in-scalars" id="built-in-scalars"><h2>Built-in scalars</h2></a>
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<p>Juniper has built-in support for:</p>
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<ul>
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<li><code>i32</code> as <code>Int</code></li>
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<li><code>f64</code> as <code>Float</code></li>
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<li><code>String</code> and <code>&str</code> as <code>String</code></li>
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<li><code>bool</code> as <code>Boolean</code></li>
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<li><code>juniper::ID</code> as <code>ID</code>. This type is defined <a href="http://facebook.github.io/graphql/#sec-ID">in the
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spec</a> as a type that is serialized
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as a string but can be parsed from both a string and an integer.</li>
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</ul>
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<p>Note that there is no built-in support for <code>i64</code>/<code>u64</code>, as the GraphQL spec <a href="https://spec.graphql.org/June2018/#sec-Int">doesn't define any built-in scalars for <code>i64</code>/<code>u64</code> by default</a>. You may wish to leverage a <a href="#custom-scalars">custom GraphQL scalar</a> in your schema to support them.</p>
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<p><strong>Third party types</strong>:</p>
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<p>Juniper has built-in support for a few additional types from common third party
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crates. They are enabled via features that are on by default.</p>
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<ul>
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<li>uuid::Uuid</li>
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<li>chrono::DateTime</li>
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<li>time::{Date, OffsetDateTime, PrimitiveDateTime, Time, UtcOffset}</li>
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<li>url::Url</li>
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<li>bson::oid::ObjectId</li>
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</ul>
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<a class="header" href="#newtype-pattern" id="newtype-pattern"><h2>newtype pattern</h2></a>
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<p>Often, you might need a custom scalar that just wraps an existing type.</p>
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<p>This can be done with the newtype pattern and a custom derive, similar to how
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serde supports this pattern with <code>#[serde(transparent)]</code>.</p>
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<pre><pre class="playpen"><code class="language-rust"># extern crate juniper;
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#[derive(juniper::GraphQLScalarValue)]
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pub struct UserId(i32);
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#[derive(juniper::GraphQLObject)]
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struct User {
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id: UserId,
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}
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# fn main() {}
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</code></pre></pre>
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<p>That's it, you can now user <code>UserId</code> in your schema.</p>
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<p>The macro also allows for more customization:</p>
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<pre><pre class="playpen"><code class="language-rust"># extern crate juniper;
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/// You can use a doc comment to specify a description.
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#[derive(juniper::GraphQLScalarValue)]
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#[graphql(
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transparent,
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// Overwrite the GraphQL type name.
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name = "MyUserId",
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// Specify a custom description.
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// A description in the attribute will overwrite a doc comment.
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description = "My user id description",
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)]
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pub struct UserId(i32);
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# fn main() {}
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</code></pre></pre>
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<a class="header" href="#custom-scalars" id="custom-scalars"><h2>Custom scalars</h2></a>
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<p>For more complex situations where you also need custom parsing or validation,
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you can use the <code>graphql_scalar</code> proc macro.</p>
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<p>Typically, you represent your custom scalars as strings.</p>
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<p>The example below implements a custom scalar for a custom <code>Date</code> type.</p>
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<p>Note: juniper already has built-in support for the <code>chrono::DateTime</code> type
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via <code>chrono</code> feature, which is enabled by default and should be used for this
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purpose.</p>
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<p>The example below is used just for illustration.</p>
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<p><strong>Note</strong>: the example assumes that the <code>Date</code> type implements
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<code>std::fmt::Display</code> and <code>std::str::FromStr</code>.</p>
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<pre><pre class="playpen"><code class="language-rust"># extern crate juniper;
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# mod date {
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# pub struct Date;
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# impl std::str::FromStr for Date {
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# type Err = String; fn from_str(_value: &str) -> Result<Self, Self::Err> { unimplemented!() }
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# }
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# // And we define how to represent date as a string.
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# impl std::fmt::Display for Date {
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# fn fmt(&self, _f: &mut std::fmt::Formatter) -> std::fmt::Result {
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# unimplemented!()
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# }
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# }
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# }
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#
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use juniper::{Value, ParseScalarResult, ParseScalarValue};
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use date::Date;
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#[juniper::graphql_scalar(description = "Date")]
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impl<S> GraphQLScalar for Date
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where
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S: ScalarValue
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{
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// Define how to convert your custom scalar into a primitive type.
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fn resolve(&self) -> Value {
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Value::scalar(self.to_string())
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}
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// Define how to parse a primitive type into your custom scalar.
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// NOTE: The error type should implement `IntoFieldError<S>`.
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fn from_input_value(v: &InputValue) -> Result<Date, String> {
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v.as_string_value()
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.ok_or_else(|| format!("Expected `String`, found: {}", v))
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.and_then(|s| s.parse().map_err(|e| format!("Failed to parse `Date`: {}", e)))
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}
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// Define how to parse a string value.
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fn from_str<'a>(value: ScalarToken<'a>) -> ParseScalarResult<'a, S> {
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<String as ParseScalarValue<S>>::from_str(value)
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}
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}
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#
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# fn main() {}
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</code></pre></pre>
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