fix: register getter on runtime when field is of a parent type

generator/graphql-kotlin-schema-generator/src/main/kotlin/com/expediagroup/graphql/generator/execution/KotlinDataFetcherFactoryProvider.kt

@@ -66,10 +66,12 @@ open class SimpleKotlinDataFetcherFactoryProvider : KotlinDataFetcherFactoryProv
 }
 
 /**
- * [SimpleSingletonKotlinDataFetcherFactoryProvider] is a specialization of [SimpleKotlinDataFetcherFactoryProvider] that will provide a
+ * [SimpleSingletonKotlinDataFetcherFactoryProvider] is a specialization of [SimpleKotlinDataFetcherFactoryProvider] that will provide
  * a [SingletonPropertyDataFetcher] that should be used to target property resolutions without allocating a DataFetcher per property
  */
 open class SimpleSingletonKotlinDataFetcherFactoryProvider : SimpleKotlinDataFetcherFactoryProvider() {
     override fun propertyDataFetcherFactory(kClass: KClass<*>, kProperty: KProperty<*>): DataFetcherFactory<Any?> =
-        SingletonPropertyDataFetcher.getFactoryAndRegister(kClass, kProperty)
+        SingletonPropertyDataFetcher.factory.also {
+            SingletonPropertyDataFetcher.register(kClass, kProperty)
+        }
 }

generator/graphql-kotlin-schema-generator/src/main/kotlin/com/expediagroup/graphql/generator/execution/SingletonPropertyDataFetcher.kt

@@ -5,25 +5,26 @@ import graphql.schema.DataFetcherFactory
 import graphql.schema.DataFetchingEnvironment
 import graphql.schema.GraphQLFieldDefinition
 import graphql.schema.LightDataFetcher
+import org.slf4j.LoggerFactory
 import java.util.concurrent.ConcurrentHashMap
 import java.util.function.Supplier
 import kotlin.reflect.KClass
 import kotlin.reflect.KProperty
+import kotlin.reflect.full.memberProperties
 
 /**
  * Singleton Property [DataFetcher] that stores references to underlying properties getters.
  */
 internal object SingletonPropertyDataFetcher : LightDataFetcher<Any?> {
 
-    private val factory: DataFetcherFactory<Any?> = DataFetcherFactory<Any?> { SingletonPropertyDataFetcher }
-
+    private val logger = LoggerFactory.getLogger(SingletonPropertyDataFetcher::class.java)
+    val factory: DataFetcherFactory<Any?> = DataFetcherFactory<Any?> { SingletonPropertyDataFetcher }
     private val getters: ConcurrentHashMap<String, KProperty.Getter<*>> = ConcurrentHashMap()
 
-    fun getFactoryAndRegister(kClass: KClass<*>, kProperty: KProperty<*>): DataFetcherFactory<Any?> {
+    fun register(kClass: KClass<*>, kProperty: KProperty<*>) {
         getters.computeIfAbsent("${kClass.java.name}.${kProperty.name}") {
             kProperty.getter
         }
-        return factory
     }
 
     override fun get(
@@ -32,7 +33,17 @@ internal object SingletonPropertyDataFetcher : LightDataFetcher<Any?> {
         environmentSupplier: Supplier<DataFetchingEnvironment>
     ): Any? =
         sourceObject?.let {
-            getters["${sourceObject.javaClass.name}.${fieldDefinition.name}"]?.call(sourceObject)
+            getters["${sourceObject.javaClass.name}.${fieldDefinition.name}"]?.call(sourceObject) ?: run {
+                sourceObject::class.memberProperties
+                    .find { it.name == fieldDefinition.name }
+                    ?.let { kProperty ->
+                        kProperty.getter.call(sourceObject).also {
+                            register(sourceObject::class, kProperty)
+                        }
+                    }
+            } ?: run {
+                logger.error("getter method not found: ${sourceObject.javaClass.name}.${fieldDefinition.name}")
+            }
         }
 
     override fun get(environment: DataFetchingEnvironment): Any? =

generator/graphql-kotlin-schema-generator/src/test/kotlin/com/expediagroup/graphql/generator/ToSchemaTest.kt

@@ -86,6 +86,22 @@ class ToSchemaTest {
         assertEquals(1, geo?.get("query")?.get("id"))
     }
 
+    @ParameterizedTest(name = "{index} ==> {1}")
+    @MethodSource("toSchemaTestArguments")
+    fun `SchemaGenerator generates resolvers for parent classes`(provider: KotlinDataFetcherFactoryProvider, name: String) {
+        val schema = toSchema(
+            queries = listOf(TopLevelObject(QueryObject())),
+            mutations = listOf(TopLevelObject(MutationObject())),
+            config = testSchemaConfig(provider)
+        )
+        val graphQL = GraphQL.newGraphQL(schema).build()
+
+        val result = graphQL.execute(" { range { start { day } end { day } } }")
+        val data: Map<String, Map<String, Map<String, Any>>>? = result.getData()
+        assertEquals(30, data?.get("range")?.get("start")?.get("day"))
+        assertEquals(14, data?.get("range")?.get("end")?.get("day"))
+    }
+
     @ParameterizedTest(name = "{index} ==> {1}")
     @MethodSource("toSchemaTestArguments")
     fun `SchemaGenerator generates a simple GraphQL schema with default builder`(provider: KotlinDataFetcherFactoryProvider, name: String) {
@@ -405,9 +421,21 @@ class ToSchemaTest {
         fun foo(): String = "bar"
     }
 
+    open class ParentDate(val day: Int, val month: Int, val year: Int)
+
+    data class DateRange(val start: ParentDate, val end: ParentDate)
+
+    class ChildDate(day: Int, month: Int, year: Int) : ParentDate(day, month, year)
+
     class QueryObject {
         @GraphQLDescription("A GraphQL query method")
         fun query(@GraphQLDescription("A GraphQL value") value: Int): Geography = Geography(value, GeoType.CITY, listOf())
+        fun range(): DateRange {
+            return DateRange(
+                ChildDate(30, 5, 1992),
+                ChildDate(14, 6, 1992),
+            )
+        }
     }
 
     class QueryWithIgnored {