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Polishing Federation section in docs

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rstoyanchev
2024-04-15 12:21:39 +01:00
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spring-graphql-docs/modules/ROOT/pages/federation.adoc
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[[federation]]
= Federation
Spring for GraphQL provides a small integration layer for the
https://github.com/apollographql/federation-jvm[federation-jvm] library that in turn builds
on GraphQL Java, and helps to initialize the `graphql.schema.GraphQLSchema` for a GraphQL
Java application that is a sub-graph within a federated graph. For more details, see
https://www.apollographql.com/docs/federation/[Apollo Federation] and the
https://www.apollographql.com/docs/federation/subgraph-spec[Subgraph spec].
Spring for GraphQL provides an integration for the
https://github.com/apollographql/federation-jvm[federation-jvm] library, which uses
GraphQL Java to initialize the schema of a sub-graph within a federated graph.
See https://www.apollographql.com/docs/federation/[Apollo Federation] and the
https://www.apollographql.com/docs/federation/subgraph-spec[Subgraph spec] for further details.
To use the support you can declare a `FederationSchemaFactory` bean in your config, and plug
it into `GraphQlSource.Builder`. In a Spring Boot application you can do this through a
`GraphQlSourceBuilderCustomizer` as follows:
[[federation.config]]
== Config
To use the integration, declare a `FederationSchemaFactory` bean in your config, and plug
it into `GraphQlSource.Builder`. For example, in a Spring Boot application:
[source,java,indent=0,subs="verbatim,quotes"]
----
@@ -30,7 +33,7 @@ it into `GraphQlSource.Builder`. In a Spring Boot application you can do this th
}
----
Now your sub-graph schema can extend federated types:
Now the schema for the sub-graph service can extend federated types:
[source,graphql,indent=0,subs="verbatim,quotes"]
----
@@ -46,10 +49,15 @@ type Author {
}
----
To assist with resolving federated types as part of an
https://www.apollographql.com/docs/federation/subgraph-spec/#understanding-query_entities[_entities]
query, you can use `@EntityMapping` methods side by side with `@SchemaMapping` methods
for the data that the subgraph application owns. For example:
[[federation.entity-mapping]]
== `@EntityMapping`
To resolve federated types in response to the
https://www.apollographql.com/docs/federation/subgraph-spec/#understanding-query_entities[_entities query],
you can use `@EntityMapping` methods along with `@SchemaMapping` methods for types under the entity.
For example:
[source,java,indent=0,subs="verbatim,quotes"]
----
@@ -69,8 +77,14 @@ for the data that the subgraph application owns. For example:
}
----
The `@Argument` method parameters is resolved from the "representation"input map for the entity.
You can also inject the full `Map<String, Object>`. The below shows all supported arguments:
The `@Argument` method parameters is resolved from the "representation" input map for the entity.
You can also inject the full "representation" input `Map`.
[[federation.entity-mapping.signature]]
=== Method Signature
Entity mapping methods support the following arguments:
[cols="1,2"]
|===
@@ -110,6 +124,10 @@ You can also inject the full `Map<String, Object>`. The below shows all supporte
`@EntityMapping` methods can return `Mono`, `CompletableFuture`, `Callable`, or the actual entity.
[[federation.entity-mapping.exception-handling]]
=== Exception Handling
You can use `@GraphQlExceptionHandler` methods to map exceptions from `@EntityMapping`
methods to ``GraphQLError``'s. The errors will be included in the response of the
"_entities" query. Exception handler methods can be in the same controller or in an