fix: register getter on runtime when field is of a parent type (#2091)

### 📝 Description
Adding a missing use case when the registered resolver during schema
generation is from a Parent class, while on runtime the resolve object
could be an instance of a Child class, as a result, the resolver won't
be available in the getters cache.

This PR will attempt to resolve the getter using reflection and it will
store it in the getters cache, if not getter found after checking the
cache and checking the object class with reflection then a message log
will be printed

Co-authored-by: Samuel Vazquez <samvazquez@expediagroup.com>

Author: samuelAndalon

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 {