[SLING-9796] Add support for using Unions - ASF JIRA

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Details

Type: New Feature
Status: Closed
Priority: Major
Resolution: Fixed
Affects Version/s: None
Fix Version/s: GraphQL Core 0.0.8
Component/s: GraphQL
Labels:
None

Description

The current implementation of sling-org-apache-sling-graphql-core is not supporting the Union type, however there's a way to implement it.

1. Hardcoded solution just to prove what is missing.

Supporting Unions can be added by extending the buildWiring() method [3] adding the following lines

based on the graphql-java documentation [4] the TypeResolver returns the schema ObjectType based on the current result item instance

        List<UnionTypeDefinition> unionTypes = typeRegistry.getTypes(UnionTypeDefinition.class);
        for (UnionTypeDefinition type : unionTypes) {

            TypeResolver typeResolver = env -> {
                Object javaObject = env.getObject();
                 // schema contains only one union definition:
                 //     "union TestUnion = Type_1 | Type_2 | Type_3 | Type_4"
                 // hardcoding to force return the object type Type1
                 return env.getSchema().getObjectType("Type1");

            };

            builder.type(type.getName(), typeWriting -> typeWriting.typeResolver(typeResolver));
        }

2. General solution

The suggested solution would be to extend sling-org-apache-sling-graphql-core to allow TypeProviders as external callable, following the pattern how it was implemented in case of data fetchers.

Unfortunately, there's no general logic (in sling) regarding how a TypeProvider can decide which Object Type needs to be returned. The condition is based on the result item (javaObject) which is constructed by the data fetcher (external callable). Therefore, to match the logic, the TypeResolver should be callable (OSGI component) which could be detected by directives (@fecher) used by the Union type definition as follows:

# This directive maps the corresponding type resolver to a given Union
directive @resolver(
    name: String, 
    options: String = "", 
    source: String = ""
) on UNION

union TestUnion @resolver(name : "test/resolver", source : "TestUnion") = Type_1 | Type_2 | Type_3 | Type_4

[3] https://github.com/apache/sling-org-apache-sling-graphql-core/blob/19bc07c039bfb3e9d578e9c592b60c3da6bdd951/src/main/java/org/apache/sling/graphql/core/engine/GraphQLResourceQuery.java#L133
[4] https://www.graphql-java.com/documentation/v11/schema/#datafetcher-and-typeresolver