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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"><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" class="active"><strong aria-hidden="true">5.7.</strong> Subscriptions</a></li></ol></li></ol>
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<main>
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<a class="header" href="#subscriptions" id="subscriptions"><h1>Subscriptions</h1></a>
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<a class="header" href="#how-to-achieve-realtime-data-with-graphql-subscriptions" id="how-to-achieve-realtime-data-with-graphql-subscriptions"><h3>How to achieve realtime data with GraphQL subscriptions</h3></a>
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<p>GraphQL subscriptions are a way to push data from the server to clients requesting real-time messages
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from the server. Subscriptions are similar to queries in that they specify a set of fields to be delivered to the client,
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but instead of immediately returning a single answer a result is sent every time a particular event happens on the
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server.</p>
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<p>In order to execute subscriptions you need a coordinator (that spawns connections)
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and a GraphQL object that can be resolved into a stream--elements of which will then
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be returned to the end user. The <a href="https://github.com/graphql-rust/juniper/tree/master/juniper_subscriptions"><code>juniper_subscriptions</code></a> crate
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provides a default connection implementation. Currently subscriptions are only supported on the <code>master</code> branch. Add the following to your <code>Cargo.toml</code>:</p>
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<pre><code class="language-toml">[dependencies]
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juniper = { git = "https://github.com/graphql-rust/juniper", branch = "master" }
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juniper_subscriptions = { git = "https://github.com/graphql-rust/juniper", branch = "master" }
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</code></pre>
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<a class="header" href="#schema-definition" id="schema-definition"><h3>Schema Definition</h3></a>
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<p>The <code>Subscription</code> is just a GraphQL object, similar to the query root and mutations object that you defined for the
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operations in your [Schema][Schema]. For subscriptions all fields/operations should be async and should return a <a href="https://docs.rs/futures/0.3.4/futures/stream/trait.Stream.html">Stream</a>.</p>
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<p>This example shows a subscription operation that returns two events, the strings <code>Hello</code> and <code>World!</code>
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sequentially:</p>
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<pre><pre class="playpen"><code class="language-rust"># use juniper::{graphql_object, graphql_subscription, FieldError};
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# use futures::Stream;
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# use std::pin::Pin;
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#
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# #[derive(Clone)]
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# pub struct Database;
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# impl juniper::Context for Database {}
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# pub struct Query;
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# #[graphql_object(context = Database)]
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# impl Query {
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# fn hello_world() -> &'static str {
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# "Hello World!"
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# }
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# }
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pub struct Subscription;
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type StringStream = Pin<Box<dyn Stream<Item = Result<String, FieldError>> + Send>>;
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#[graphql_subscription(context = Database)]
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impl Subscription {
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async fn hello_world() -> StringStream {
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let stream = futures::stream::iter(vec![
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Ok(String::from("Hello")),
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Ok(String::from("World!"))
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]);
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Box::pin(stream)
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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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<a class="header" href="#coordinator" id="coordinator"><h3>Coordinator</h3></a>
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<p>Subscriptions require a bit more resources than regular queries and provide a great vector for DOS attacks. This can can bring down a server easily if not handled correctly. The [<code>SubscriptionCoordinator</code>][SubscriptionCoordinator] trait provides coordination logic to enable functionality like DOS attack mitigation and resource limits.</p>
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<p>The [<code>SubscriptionCoordinator</code>][SubscriptionCoordinator] contains the schema and can keep track of opened connections, handle subscription
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start and end, and maintain a global subscription id for each subscription. Each time a connection is established,<br />
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the [<code>SubscriptionCoordinator</code>][SubscriptionCoordinator] spawns a [<code>SubscriptionConnection</code>][SubscriptionConnection]. The [<code>SubscriptionConnection</code>][SubscriptionConnection] handles a single connection, providing resolver logic for a client stream as well as reconnection
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and shutdown logic.</p>
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<p>While you can implement [<code>SubscriptionCoordinator</code>][SubscriptionCoordinator] yourself, Juniper contains a simple and generic implementation called [<code>Coordinator</code>][Coordinator]. The <code>subscribe</code>
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operation returns a [<code>Future</code>][Future] with an <code>Item</code> value of a <code>Result<Connection, GraphQLError></code>,
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where [<code>Connection</code>][Connection] is a <code>Stream</code> of values returned by the operation and [<code>GraphQLError</code>][GraphQLError] is the error when the subscription fails.</p>
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<pre><pre class="playpen"><code class="language-rust"># #![allow(dead_code)]
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# extern crate futures;
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# extern crate juniper;
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# extern crate juniper_subscriptions;
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# extern crate serde_json;
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# extern crate tokio;
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# use juniper::{
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# http::GraphQLRequest,
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# graphql_object, graphql_subscription,
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# DefaultScalarValue, EmptyMutation, FieldError,
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# RootNode, SubscriptionCoordinator,
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# };
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# use juniper_subscriptions::Coordinator;
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# use futures::{Stream, StreamExt};
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# use std::pin::Pin;
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#
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# #[derive(Clone)]
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# pub struct Database;
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#
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# impl juniper::Context for Database {}
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#
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# impl Database {
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# fn new() -> Self {
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# Self {}
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# }
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# }
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#
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# pub struct Query;
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#
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# #[graphql_object(context = Database)]
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# impl Query {
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# fn hello_world() -> &'static str {
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# "Hello World!"
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# }
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# }
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#
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# pub struct Subscription;
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#
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# type StringStream = Pin<Box<dyn Stream<Item = Result<String, FieldError>> + Send>>;
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#
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# #[graphql_subscription(context = Database)]
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# impl Subscription {
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# async fn hello_world() -> StringStream {
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# let stream =
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# futures::stream::iter(vec![Ok(String::from("Hello")), Ok(String::from("World!"))]);
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# Box::pin(stream)
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# }
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# }
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type Schema = RootNode<'static, Query, EmptyMutation<Database>, Subscription>;
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fn schema() -> Schema {
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Schema::new(Query {}, EmptyMutation::new(), Subscription {})
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}
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async fn run_subscription() {
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let schema = schema();
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let coordinator = Coordinator::new(schema);
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let req: GraphQLRequest<DefaultScalarValue> = serde_json::from_str(
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r#"{
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"query": "subscription { helloWorld }"
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}"#,
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)
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.unwrap();
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let ctx = Database::new();
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let mut conn = coordinator.subscribe(&req, &ctx).await.unwrap();
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while let Some(result) = conn.next().await {
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println!("{}", serde_json::to_string(&result).unwrap());
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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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<a class="header" href="#web-integration-and-examples" id="web-integration-and-examples"><h3>Web Integration and Examples</h3></a>
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||
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<p>Currently there is an example of subscriptions with [warp][warp], but it still in an alpha state.
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||
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GraphQL over [WS][WS] is not fully supported yet and is non-standard.</p>
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<ul>
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<li><a href="https://github.com/graphql-rust/juniper/tree/master/examples/warp_subscriptions">Warp Subscription Example</a></li>
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|
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<li><a href="https://github.com/graphql-rust/juniper/tree/master/examples/basic_subscriptions">Small Example</a></li>
|
||
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</ul>
|
||
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<!-- TODO: Fix these links when the documentation for the `juniper_subscriptions` are defined in the docs. --->
|
||
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[Coordinator]: https://docs.rs/juniper_subscriptions/0.15.0/struct.Coordinator.html
|
||
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[SubscriptionCoordinator]: https://docs.rs/juniper_subscriptions/0.15.0/trait.SubscriptionCoordinator.html
|
||
|
|
[Connection]: https://docs.rs/juniper_subscriptions/0.15.0/struct.Connection.html
|
||
|
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[SubscriptionConnection]: https://docs.rs/juniper_subscriptions/0.15.0/trait.SubscriptionConnection.html
|
||
|
|
<!--- --->
|
||
|
|
[Future]: https://docs.rs/futures/0.3.4/futures/future/trait.Future.html
|
||
|
|
[warp]: https://github.com/graphql-rust/juniper/tree/master/juniper_warp
|
||
|
|
[WS]: https://github.com/apollographql/subscriptions-transport-ws/blob/master/PROTOCOL.md
|
||
|
|
[GraphQLError]: https://docs.rs/juniper/0.14.2/juniper/enum.GraphQLError.html
|
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|
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[Schema]: ../schema/schemas_and_mutations.md
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