feat: support data and errors with DataFetcherResult

Fixes ExpediaGroup#244

Kotlin functions can now return a  instead of just their return type which allows you to modify the errors field with any extra data you need

Author: smyrick

README.md

@@ -100,4 +100,4 @@ If you have a question about something you can not find in our wiki or javadocs,
 
 One way to run a GraphQL server is with Spring Boot. A sample Spring Boot app that uses [Spring Webflux](https://docs.spring.io/spring/docs/current/spring-framework-reference/web-reactive.html) together with `graphql-kotlin` and [graphql-playground](https://github.com/prisma/graphql-playground) is provided in the [example folder](https://github.com/ExpediaDotCom/graphql-kotlin/tree/master/example). All the examples used in this documentation should be available in the sample app.
 
-In order to run it you can run [Application.kt](https://github.com/ExpediaDotCom/graphql-kotlin/blob/master/example/src/main/kotlin/com.expedia.graphql.sample/Application.kt) directly from your IDE. Alternatively you can also use the Spring Boot maven plugin by running `mvn spring-boot:run` from the command line. Once the app has started you can explore the example schema by opening GraphiQL endpoint at [http://localhost:8080/playground](http://localhost:8080/playground).
+In order to run it you can run [Application.kt](https://github.com/ExpediaDotCom/graphql-kotlin/blob/master/example/src/main/kotlin/com.expedia.graphql.sample/Application.kt) directly from your IDE. Alternatively you can also use the Spring Boot maven plugin by running `mvn spring-boot:run` from the command line. Once the app has started you can explore the example schema by opening the Playground endpoint at [http://localhost:8080/playground](http://localhost:8080/playground).

example/README.md

@@ -16,4 +16,4 @@ Start the server:
 * Alternatively you can also use the spring boot maven plugin by running `mvn spring-boot:run` from the command line.
 
 
-Once the app has started you can explore the example schema by opening Playground endpoint at http://localhost:8080/playground.
+Once the app has started you can explore the example schema by opening the Playground endpoint at http://localhost:8080/playground.

example/src/main/kotlin/com/expedia/graphql/sample/query/DataAndErrors.kt

@@ -0,0 +1,16 @@
+package com.expedia.graphql.sample.query
+
+import graphql.ExceptionWhileDataFetching
+import graphql.execution.DataFetcherResult
+import graphql.execution.ExecutionPath
+import graphql.language.SourceLocation
+import org.springframework.stereotype.Component
+
+@Component
+class DataAndErrors : Query {
+
+    fun returnDataAndErrors(): DataFetcherResult<String> {
+        val error = ExceptionWhileDataFetching(ExecutionPath.rootPath(), RuntimeException(), SourceLocation(1, 1))
+        return DataFetcherResult("Hello from data fetcher", listOf(error))
+    }
+}

src/main/kotlin/com/expedia/graphql/generator/types/FunctionBuilder.kt

@@ -13,6 +13,7 @@ import com.expedia.graphql.generator.extensions.isGraphQLContext
 import com.expedia.graphql.generator.extensions.isGraphQLIgnored
 import com.expedia.graphql.generator.extensions.isInterface
 import com.expedia.graphql.generator.extensions.safeCast
+import graphql.execution.DataFetcherResult
 import graphql.schema.FieldCoordinates
 import graphql.schema.GraphQLArgument
 import graphql.schema.GraphQLFieldDefinition
@@ -51,7 +52,8 @@ internal class FunctionBuilder(generator: SchemaGenerator) : TypeBuilder(generat
 
         val typeFromHooks = config.hooks.willResolveMonad(fn.returnType)
         val returnType = getWrappedReturnType(typeFromHooks)
-        builder.type(graphQLTypeOf(returnType).safeCast<GraphQLOutputType>())
+        val graphQLOutputType = graphQLTypeOf(returnType).safeCast<GraphQLOutputType>()
+        builder.type(graphQLOutputType)
         val graphQLType = builder.build()
 
         val coordinates = FieldCoordinates.coordinates(parentName, fn.name)
@@ -63,10 +65,19 @@ internal class FunctionBuilder(generator: SchemaGenerator) : TypeBuilder(generat
         return config.hooks.onRewireGraphQLType(graphQLType, coordinates, codeRegistry).safeCast()
     }
 
+    /**
+     * These are the classes that can be returned from data fetchers (ie functions)
+     * but we only want to expose the wrapped type in the schema.
+     *
+     * [Publisher] is used for subscriptions
+     * [CompletableFuture] is used for asynchronous results
+     * [DataFetcherResult] is used for returning data and errors in the same response
+     */
     private fun getWrappedReturnType(returnType: KType): KType =
         when {
             returnType.getKClass().isSubclassOf(Publisher::class) -> returnType.getTypeOfFirstArgument()
             returnType.classifier == CompletableFuture::class -> returnType.getTypeOfFirstArgument()
+            returnType.classifier == DataFetcherResult::class -> returnType.getTypeOfFirstArgument()
             else -> returnType
         }
 

src/test/kotlin/com/expedia/graphql/generator/SchemaGeneratorTest.kt

@@ -11,8 +11,12 @@ import com.expedia.graphql.exceptions.InvalidIdTypeException
 import com.expedia.graphql.extensions.deepName
 import com.expedia.graphql.testSchemaConfig
 import com.expedia.graphql.toSchema
+import graphql.ExceptionWhileDataFetching
 import graphql.GraphQL
 import graphql.Scalars
+import graphql.execution.DataFetcherResult
+import graphql.execution.ExecutionPath
+import graphql.language.SourceLocation
 import graphql.schema.GraphQLNonNull
 import graphql.schema.GraphQLObjectType
 import org.junit.jupiter.api.Test
@@ -288,6 +292,23 @@ class SchemaGeneratorTest {
         assertEquals(Scalars.GraphQLID, serialField?.wrappedType)
     }
 
+    @Test
+    fun `SchemaGenerator supports DataFetcherResult as a return type`() {
+        val schema = toSchema(queries = listOf(TopLevelObject(QueryWithDataFetcherResult())), config = testSchemaConfig)
+
+        val graphQL = GraphQL.newGraphQL(schema).build()
+        val result = graphQL.execute("{ dataAndErrors }")
+        val data = result.getData<Map<String, String>>()
+        val errors = result.errors
+
+        assertNotNull(data)
+        val res: String? = data["dataAndErrors"]
+        assertEquals(actual = res, expected = "Hello")
+
+        assertNotNull(errors)
+        assertEquals(expected = 1, actual = errors.size)
+    }
+
     class QueryObject {
         @GraphQLDescription("A GraphQL query method")
         fun query(@GraphQLDescription("A GraphQL value") value: Int): Geography = Geography(value, GeoType.CITY, listOf())
@@ -485,4 +506,11 @@ class SchemaGeneratorTest {
         @GraphQLID val serial: UUID,
         val type: String
     )
+
+    class QueryWithDataFetcherResult {
+        fun dataAndErrors(): DataFetcherResult<String> {
+            val error = ExceptionWhileDataFetching(ExecutionPath.rootPath(), RuntimeException(), SourceLocation(1, 1))
+            return DataFetcherResult.newResult<String>().data("Hello").error(error).build()
+        }
+    }
 }

src/test/kotlin/com/expedia/graphql/generator/types/FunctionBuilderTest.kt

@@ -5,8 +5,12 @@ import com.expedia.graphql.annotations.GraphQLDescription
 import com.expedia.graphql.annotations.GraphQLDirective
 import com.expedia.graphql.annotations.GraphQLIgnore
 import com.expedia.graphql.execution.FunctionDataFetcher
+import graphql.ExceptionWhileDataFetching
 import graphql.Scalars
+import graphql.execution.DataFetcherResult
+import graphql.execution.ExecutionPath
 import graphql.introspection.Introspection
+import graphql.language.SourceLocation
 import graphql.schema.DataFetchingEnvironment
 import graphql.schema.FieldCoordinates
 import graphql.schema.GraphQLNonNull
@@ -64,6 +68,11 @@ internal class FunctionBuilderTest : TypeTestHelper() {
         fun completableFuture(num: Int): CompletableFuture<Int> = CompletableFuture.completedFuture(num)
 
         fun dataFetchingEnvironment(environment: DataFetchingEnvironment): String = environment.field.name
+
+        fun dataFetcherResult(): DataFetcherResult<String> {
+            val error = ExceptionWhileDataFetching(ExecutionPath.rootPath(), RuntimeException(), SourceLocation(1, 1))
+            return DataFetcherResult.newResult<String>().data("Hello").error(error).build()
+        }
     }
 
     @Test
@@ -208,4 +217,12 @@ internal class FunctionBuilderTest : TypeTestHelper() {
         assertEquals(expected = 0, actual = result.arguments.size)
         assertEquals("String", (result.type as? GraphQLNonNull)?.wrappedType?.name)
     }
+
+    @Test
+    fun `DataFetcherResult return type is valid and unwrapped in the schema`() {
+        val kFunction = Happy::dataFetcherResult
+        val result = builder.function(fn = kFunction, parentName = "Query")
+
+        assertEquals("String", (result.type as? GraphQLNonNull)?.wrappedType?.name)
+    }
 }