Enable support for specifying custom DataFetchers (#152)

* Enable coroutine support in default KotlinDataFetcher

* Enable support for specifying custom DataFetchers

* fix compilation errors

* simplify KotlinDataFetcherFactoryProvider

* add accidentally removed data fetcher tests

* renaming variable name

example/src/main/kotlin/com/expedia/graphql/sample/Application.kt

@@ -3,7 +3,10 @@ package com.expedia.graphql.sample
 import com.expedia.graphql.DirectiveWiringHelper
 import com.expedia.graphql.SchemaGeneratorConfig
 import com.expedia.graphql.TopLevelObject
+import com.expedia.graphql.execution.KotlinDataFetcherFactoryProvider
+import com.expedia.graphql.hooks.SchemaGeneratorHooks
 import com.expedia.graphql.sample.context.MyGraphQLContextBuilder
+import com.expedia.graphql.sample.dataFetchers.CustomDataFetcherFactoryProvider
 import com.expedia.graphql.sample.dataFetchers.SpringDataFetcherFactory
 import com.expedia.graphql.sample.directives.DirectiveWiringFactory
 import com.expedia.graphql.sample.directives.LowercaseDirectiveWiring
@@ -42,10 +45,18 @@ class Application {
     fun wiringFactory() = DirectiveWiringFactory()
 
     @Bean
-    fun schemaConfig(dataFetcherFactory: SpringDataFetcherFactory, validator: Validator, wiringFactory: DirectiveWiringFactory): SchemaGeneratorConfig = SchemaGeneratorConfig(
+    fun hooks(validator: Validator, wiringFactory: DirectiveWiringFactory) =
+            CustomSchemaGeneratorHooks(validator, DirectiveWiringHelper(wiringFactory, mapOf("lowercase" to LowercaseDirectiveWiring())))
+
+    @Bean
+    fun dataFetcherFactoryProvider(springDataFetcherFactory: SpringDataFetcherFactory, hooks: SchemaGeneratorHooks) =
+            CustomDataFetcherFactoryProvider(springDataFetcherFactory, hooks)
+
+    @Bean
+    fun schemaConfig(hooks: SchemaGeneratorHooks, dataFetcherFactoryProvider: KotlinDataFetcherFactoryProvider): SchemaGeneratorConfig = SchemaGeneratorConfig(
         supportedPackages = listOf("com.expedia"),
-        hooks = CustomSchemaGeneratorHooks(validator, DirectiveWiringHelper(wiringFactory, mapOf("lowercase" to LowercaseDirectiveWiring()))),
-        dataFetcherFactory = dataFetcherFactory
+        hooks = hooks,
+        dataFetcherFactoryProvider = dataFetcherFactoryProvider
     )
 
     @Bean

example/src/main/kotlin/com/expedia/graphql/sample/dataFetchers/CustomDataFetcherFactoryProvider.kt

@@ -0,0 +1,23 @@
+package com.expedia.graphql.sample.dataFetchers
+
+import com.expedia.graphql.execution.KotlinDataFetcherFactoryProvider
+import com.expedia.graphql.hooks.SchemaGeneratorHooks
+import graphql.schema.DataFetcherFactory
+import kotlin.reflect.KClass
+import kotlin.reflect.KProperty
+
+/**
+ * Custom DataFetcherFactory provider that returns custom Spring based DataFetcherFactory for resolving lateinit properties.
+ */
+class CustomDataFetcherFactoryProvider(
+        private val springDataFetcherFactory: SpringDataFetcherFactory,
+        hooks: SchemaGeneratorHooks
+) : KotlinDataFetcherFactoryProvider(hooks) {
+
+    override fun propertyDataFetcherFactory(kClazz: KClass<*>, kProperty: KProperty<*>): DataFetcherFactory<Any> =
+        if (kProperty.isLateinit) {
+            springDataFetcherFactory
+        } else {
+            super.propertyDataFetcherFactory(kClazz, kProperty)
+        }
+}

example/src/main/kotlin/com/expedia/graphql/sample/extension/CustomSchemaGeneratorHooks.kt

@@ -1,7 +1,7 @@
 package com.expedia.graphql.sample.extension
 
 import com.expedia.graphql.DirectiveWiringHelper
-import com.expedia.graphql.hooks.DataFetcherExecutionPredicate
+import com.expedia.graphql.execution.DataFetcherExecutionPredicate
 import com.expedia.graphql.hooks.SchemaGeneratorHooks
 import com.expedia.graphql.sample.validation.DataFetcherExecutionValidator
 import graphql.language.StringValue

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

@@ -11,7 +11,7 @@ import org.springframework.stereotype.Component
  * schema and will be automatically autowired at runtime using value from the environment.
  *
  * @see com.expedia.graphql.sample.context.MyGraphQLContextBuilder
- * @see com.expedia.graphql.KotlinDataFetcher
+ * @see com.expedia.graphql.FunctionDataFetcher
  */
 @Component
 class ContextualQuery: Query {

example/src/main/kotlin/com/expedia/graphql/sample/validation/DataFetcherExecutionValidator.kt

@@ -1,6 +1,6 @@
 package com.expedia.graphql.sample.validation
 
-import com.expedia.graphql.hooks.DataFetcherExecutionPredicate
+import com.expedia.graphql.execution.DataFetcherExecutionPredicate
 import com.expedia.graphql.sample.exceptions.ValidationException
 import com.expedia.graphql.sample.exceptions.asConstraintError
 import graphql.schema.DataFetchingEnvironment

src/main/kotlin/com/expedia/graphql/SchemaGeneratorConfig.kt

@@ -1,8 +1,8 @@
 package com.expedia.graphql
 
+import com.expedia.graphql.execution.KotlinDataFetcherFactoryProvider
 import com.expedia.graphql.hooks.NoopSchemaGeneratorHooks
 import com.expedia.graphql.hooks.SchemaGeneratorHooks
-import graphql.schema.DataFetcherFactory
 
 /**
  * Settings for generating the schema.
@@ -12,5 +12,5 @@ data class SchemaGeneratorConfig(
     val topLevelQueryName: String = "TopLevelQuery",
     val topLevelMutationName: String = "TopLevelMutation",
     val hooks: SchemaGeneratorHooks = NoopSchemaGeneratorHooks(),
-    val dataFetcherFactory: DataFetcherFactory<*>? = null
+    val dataFetcherFactoryProvider: KotlinDataFetcherFactoryProvider = KotlinDataFetcherFactoryProvider(hooks)
 )

src/main/kotlin/com/expedia/graphql/hooks/DataFetcherExecutionPredicate.kt → src/main/kotlin/com/expedia/graphql/execution/DataFetcherExecutionPredicate.kt

@@ -1,10 +1,10 @@
-package com.expedia.graphql.hooks
+package com.expedia.graphql.execution
 
 import graphql.schema.DataFetchingEnvironment
 import kotlin.reflect.KParameter
 
 /**
- * Perform runtime evaluations of each parameter passed to any KotlinDataFetcher.
+ * Perform runtime evaluations of each parameter passed to any FunctionDataFetcher.
  *
  * The DataFetcherExecutionPredicate is declared globally for all the datafetchers instances and all the parameters.
  * However a more precise logic (at the field level) is possible depending on the implement of `evaluate`

src/main/kotlin/com/expedia/graphql/KotlinDataFetcher.kt → src/main/kotlin/com/expedia/graphql/execution/FunctionDataFetcher.kt

@@ -1,9 +1,9 @@
-package com.expedia.graphql
+package com.expedia.graphql.execution
 
 import com.expedia.graphql.generator.extensions.getName
 import com.expedia.graphql.generator.extensions.isGraphQLContext
 import com.expedia.graphql.generator.extensions.javaTypeClass
-import com.expedia.graphql.hooks.DataFetcherExecutionPredicate
+import com.fasterxml.jackson.databind.ObjectMapper
 import com.fasterxml.jackson.module.kotlin.jacksonObjectMapper
 import graphql.schema.DataFetcher
 import graphql.schema.DataFetchingEnvironment
@@ -16,16 +16,19 @@ import kotlin.reflect.full.callSuspend
 import kotlin.reflect.full.valueParameters
 
 /**
- * Simple DataFetcher that invokes function on the target object.
+ * Simple DataFetcher that invokes target function on the given object.
  *
- * @param target The target object that performs the data fetching
+ * @param target The target object that performs the data fetching, if not specified then this data fetcher will attempt
+ *   to use source object from the environment
  * @param fn The Kotlin function being invoked
+ * @param objectMapper Jackson ObjectMapper that will be used to deserialize environment arguments to the expected function arguments
  * @param executionPredicate Predicate to run to map the value to a new result
  */
-class KotlinDataFetcher(
+class FunctionDataFetcher(
     private val target: Any?,
     private val fn: KFunction<*>,
-    private val executionPredicate: DataFetcherExecutionPredicate?
+    private val objectMapper: ObjectMapper = jacksonObjectMapper(),
+    private val executionPredicate: DataFetcherExecutionPredicate? = null
 ) : DataFetcher<Any> {
 
     @Suppress("Detekt.SpreadOperator")
@@ -51,13 +54,9 @@ class KotlinDataFetcher(
         } else {
             val name = param.getName()
             val klazz = param.type.javaTypeClass
-            val value = mapper.convertValue(environment.arguments[name], klazz)
+            val value = objectMapper.convertValue(environment.arguments[name], klazz)
             val predicateResult = executionPredicate?.evaluate(value = value, parameter = param, environment = environment)
 
             predicateResult ?: value
         }
-
-    private companion object {
-        private val mapper = jacksonObjectMapper()
-    }
 }

src/main/kotlin/com/expedia/graphql/execution/KotlinDataFetcherFactoryProvider.kt

@@ -0,0 +1,43 @@
+package com.expedia.graphql.execution
+
+import com.expedia.graphql.hooks.SchemaGeneratorHooks
+import com.fasterxml.jackson.module.kotlin.jacksonObjectMapper
+import graphql.schema.DataFetcherFactories
+import graphql.schema.DataFetcherFactory
+import graphql.schema.PropertyDataFetcher
+import kotlin.reflect.KClass
+import kotlin.reflect.KFunction
+import kotlin.reflect.KProperty
+
+/**
+ * DataFetcherFactoryProvider is used during schema construction to obtain [DataFetcherFactory] that should be used
+ * for target function and property resolution.
+ */
+open class KotlinDataFetcherFactoryProvider(private val hooks: SchemaGeneratorHooks) {
+
+    private val defaultObjectMapper = jacksonObjectMapper()
+
+    /**
+     * Retrieve instance of [DataFetcherFactory] that will be used to resolve target function.
+     *
+     * @param target target object that performs the data fetching or NULL if target object should be dynamically
+     * retrieved during data fetcher execution from [graphql.schema.DataFetchingEnvironment]
+     * @param kFunction Kotlin function being invoked
+     */
+    open fun functionDataFetcherFactory(target: Any?, kFunction: KFunction<*>): DataFetcherFactory<Any> =
+            DataFetcherFactories.useDataFetcher(
+                FunctionDataFetcher(
+                        target = target,
+                        fn = kFunction,
+                        objectMapper = defaultObjectMapper,
+                        executionPredicate = hooks.dataFetcherExecutionPredicate))
+
+    /**
+     * Retrieve instance of [DataFetcherFactory] that will be used to resolve target property.
+     *
+     * @param kClass parent class that contains this property
+     * @param kProperty Kotlin property that should be resolved
+     */
+    open fun propertyDataFetcherFactory(kClass: KClass<*>, kProperty: KProperty<*>): DataFetcherFactory<Any> =
+            DataFetcherFactories.useDataFetcher(PropertyDataFetcher(kProperty.name))
+}

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

@@ -1,6 +1,5 @@
 package com.expedia.graphql.generator.types
 
-import com.expedia.graphql.KotlinDataFetcher
 import com.expedia.graphql.exceptions.InvalidInputFieldTypeException
 import com.expedia.graphql.generator.SchemaGenerator
 import com.expedia.graphql.generator.TypeBuilder
@@ -41,9 +40,7 @@ internal class FunctionTypeBuilder(generator: SchemaGenerator) : TypeBuilder(gen
             }
 
         if (!abstract) {
-            val dataFetcher = KotlinDataFetcher(target, fn, config.hooks.dataFetcherExecutionPredicate)
-            val hookDataFetcher = config.hooks.didGenerateDataFetcher(fn, dataFetcher)
-            builder.dataFetcher(hookDataFetcher)
+            builder.dataFetcherFactory(config.dataFetcherFactoryProvider.functionDataFetcherFactory(target = target, kFunction = fn))
         }
 
         val monadType = config.hooks.willResolveMonad(fn.returnType)

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

@@ -5,9 +5,7 @@ import com.expedia.graphql.generator.TypeBuilder
 import com.expedia.graphql.generator.extensions.getPropertyDeprecationReason
 import com.expedia.graphql.generator.extensions.getPropertyDescription
 import com.expedia.graphql.generator.extensions.isPropertyGraphQLID
-import graphql.schema.DataFetcherFactory
 import graphql.schema.GraphQLFieldDefinition
-import graphql.schema.GraphQLNonNull
 import graphql.schema.GraphQLOutputType
 import kotlin.reflect.KClass
 import kotlin.reflect.KProperty
@@ -21,29 +19,14 @@ internal class PropertyTypeBuilder(generator: SchemaGenerator) : TypeBuilder(gen
             .description(prop.getPropertyDescription(parentClass))
             .name(prop.name)
             .type(propertyType)
+            .dataFetcherFactory(config.dataFetcherFactoryProvider.propertyDataFetcherFactory(kClass = parentClass, kProperty = prop))
             .deprecate(prop.getPropertyDeprecationReason(parentClass))
 
         generator.directives(prop).forEach {
             fieldBuilder.withDirective(it)
         }
 
-        val field = if (config.dataFetcherFactory != null && prop.isLateinit) {
-            updatePropertyFieldBuilder(propertyType, fieldBuilder, config.dataFetcherFactory)
-        } else {
-            fieldBuilder
-        }.build()
-
+        val field = fieldBuilder.build()
         return config.hooks.onRewireGraphQLType(prop.returnType, field) as GraphQLFieldDefinition
     }
-
-    private fun updatePropertyFieldBuilder(propertyType: GraphQLOutputType, fieldBuilder: GraphQLFieldDefinition.Builder, dataFetcherFactory: DataFetcherFactory<*>?): GraphQLFieldDefinition.Builder {
-        val updatedFieldBuilder = if (propertyType is GraphQLNonNull) {
-            val graphQLOutputType = propertyType.wrappedType as? GraphQLOutputType
-            if (graphQLOutputType != null) fieldBuilder.type(graphQLOutputType) else fieldBuilder
-        } else {
-            fieldBuilder
-        }
-
-        return updatedFieldBuilder.dataFetcherFactory(dataFetcherFactory)
-    }
 }

src/main/kotlin/com/expedia/graphql/hooks/SchemaGeneratorHooks.kt

@@ -1,7 +1,7 @@
 package com.expedia.graphql.hooks
 
+import com.expedia.graphql.execution.DataFetcherExecutionPredicate
 import com.expedia.graphql.generator.extensions.getTypeOfFirstArgument
-import graphql.schema.DataFetcher
 import graphql.schema.GraphQLFieldDefinition
 import graphql.schema.GraphQLSchema
 import graphql.schema.GraphQLType
@@ -73,12 +73,6 @@ interface SchemaGeneratorHooks {
      */
     fun didGenerateGraphQLType(type: KType, generatedType: GraphQLType) = Unit
 
-    /**
-     * Called after converting the function to a data fetcher allowing wrapping the fetcher to modify data or instrument it.
-     * This is more useful than the graphql.execution.instrumentation.Instrumentation as you have the function type here
-     */
-    fun didGenerateDataFetcher(function: KFunction<*>, dataFetcher: DataFetcher<*>): DataFetcher<*> = dataFetcher
-
     /**
      * Called after converting the function to a field definition but before adding to the schema to allow customization
      */

src/test/kotlin/com/expedia/graphql/dataFetchers/CustomDataFetcherTests.kt → src/test/kotlin/com/expedia/graphql/execution/CustomDataFetcherTests.kt

@@ -1,25 +1,28 @@
-package com.expedia.graphql.dataFetchers
+package com.expedia.graphql.execution
 
-import com.expedia.graphql.TopLevelObject
 import com.expedia.graphql.SchemaGeneratorConfig
+import com.expedia.graphql.TopLevelObject
 import com.expedia.graphql.extensions.deepName
+import com.expedia.graphql.hooks.NoopSchemaGeneratorHooks
 import com.expedia.graphql.toSchema
 import graphql.GraphQL
 import graphql.schema.DataFetcher
+import graphql.schema.DataFetcherFactories
 import graphql.schema.DataFetcherFactory
-import graphql.schema.DataFetcherFactoryEnvironment
 import graphql.schema.DataFetchingEnvironment
 import org.junit.jupiter.api.Test
+import kotlin.reflect.KClass
+import kotlin.reflect.KProperty
 import kotlin.test.assertEquals
 
 class CustomDataFetcherTests {
     @Test
     fun `Custom DataFetcher can be used on functions`() {
-        val config = SchemaGeneratorConfig(supportedPackages = listOf("com.expedia"), dataFetcherFactory = PetDataFetcherFactory())
+        val config = SchemaGeneratorConfig(supportedPackages = listOf("com.expedia"), dataFetcherFactoryProvider = CustomDataFetcherFactoryProvider())
         val schema = toSchema(listOf(TopLevelObject(AnimalQuery())), config = config)
 
         val animalType = schema.getObjectType("Animal")
-        assertEquals("AnimalDetails", animalType.getFieldDefinition("details").type.deepName)
+        assertEquals("AnimalDetails!", animalType.getFieldDefinition("details").type.deepName)
 
         val graphQL = GraphQL.newGraphQL(schema).build()
         val execute = graphQL.execute("{ findAnimal { id type details { specialId } } }")
@@ -46,8 +49,14 @@ data class Animal(
 
 data class AnimalDetails(val specialId: Int)
 
-class PetDataFetcherFactory : DataFetcherFactory<Any> {
-    override fun get(environment: DataFetcherFactoryEnvironment?): DataFetcher<Any> = AnimalDetailsDataFetcher()
+class CustomDataFetcherFactoryProvider : KotlinDataFetcherFactoryProvider(NoopSchemaGeneratorHooks()) {
+
+    override fun propertyDataFetcherFactory(kClazz: KClass<*>, kProperty: KProperty<*>): DataFetcherFactory<Any> =
+        if (kProperty.isLateinit) {
+            DataFetcherFactories.useDataFetcher(AnimalDetailsDataFetcher())
+        } else {
+            super.propertyDataFetcherFactory(kClazz, kProperty)
+        }
 }
 
 class AnimalDetailsDataFetcher : DataFetcher<Any> {

src/test/kotlin/com/expedia/graphql/dataFetchers/DataFetchPredicateTests.kt → src/test/kotlin/com/expedia/graphql/execution/DataFetchPredicateTests.kt

@@ -1,9 +1,8 @@
-package com.expedia.graphql.dataFetchers
+package com.expedia.graphql.execution
 
 import com.expedia.graphql.TopLevelObject
 import com.expedia.graphql.exceptions.GraphQLKotlinException
 import com.expedia.graphql.getTestSchemaConfigWithHooks
-import com.expedia.graphql.hooks.DataFetcherExecutionPredicate
 import com.expedia.graphql.hooks.SchemaGeneratorHooks
 import com.expedia.graphql.toSchema
 import graphql.ExceptionWhileDataFetching