Add bean factory example and docs (#657)

* Add bean factory example and docs

* Consolidate nested arguments docs

* Rename file

Co-authored-by: Shane Myrick <[email protected]>

Author: smyrick

docs/writing-schemas/nested-fields.md

@@ -0,0 +1,100 @@
+---
+id: nested-fields
+title: Nested Fields
+---
+
+There are a few ways in which you can access data in a query from different levels of arguments. Say we have the following schema:
+
+```graphql
+type Query {
+  findUser(name: String!): User
+}
+
+type User {
+  id: ID!
+  photos(numberOfPhotos: Int!): [Photo!]!
+}
+
+type Photo {
+  url: String!
+}
+```
+
+In Kotlin code, when we are in the `photos` function, if we want access to the parent field `findUser` and its
+arguments there are a couple ways we can access it:
+
+
+## DataFetchingEnvironment
+You can add the `DataFetchingEnvironment` as an argument which will allow you to view the entire query sent to the
+  server. See more in the [DataFetchingEnvironment documentation](../execution/data-fetching-environment)
+
+```kotlin
+class User {
+    fun photos(environment: DataFetchingEnvironment, numberOfPhotos: Int): List<Photo> {
+      val username = environment.executionStepInfo.parent.arguments["name"]
+      return getPhotosFromDataSource(username, numberOfPhotos)
+    }
+}
+```
+
+## GraphQL Context
+You can add the `GraphQLContext` as an argument which will allow you to view the context object you set up in the
+  data fetchers. See more in the [GraphQLContext documentation](../execution/contextual-data)
+
+```kotlin
+class User {
+    fun photos(context: MyContextObject, numberOfPhotos: Int): List<Photo> {
+      val username = context.getDataFromMyCustomFunction()
+      return getPhotosFromDataSource(username, numberOfPhotos)
+    }
+}
+```
+
+## Exluding from the Schema
+You can construct the child objects by passing down arguments as non-public fields or annotate the argument with [@GraphQLIgnore](../customizing-schemas/excluding-fields)
+
+```kotlin
+class User(private val username: String) {
+
+    fun photosProperty(numberOfPhotos: Int): List<Photo> {
+      return getPhotosFromDataSource(username, numberOfPhotos)
+    }
+
+    fun photosIgnore(@GraphQLIgnore username: String, numberOfPhotos: Int): List<Photo> {
+      return getPhotosFromDataSource(username, numberOfPhotos)
+    }
+}
+```
+
+## Spring BeanFactoryAware
+You can use Spring beans to wire different objects together at runtime.
+There is an example of how to set this up in the example app in [TopLevelBeanFactoryQuery.kt](https://github.com/ExpediaGroup/graphql-kotlin/blob/master/examples/spring/src/main/kotlin/com/expediagroup/graphql/examples/query/TopLevelBeanFactoryQuery.kt)
+
+```kotlin
+@Component
+class UsersQuery : Query, BeanFactoryAware {
+    private lateinit var beanFactory: BeanFactory
+
+    @GraphQLIgnore
+    override fun setBeanFactory(beanFactory: BeanFactory) {
+        this.beanFactory = beanFactory
+    }
+
+    fun findUser(name: String): SubQuery = beanFactory.getBean(User::class.java, name)
+}
+
+@Component
+@Scope("prototype")
+class User @Autowired(required = false) constructor(internal val userName: String) {
+
+    @Autowired
+    private lateinit var service: PhotoService
+
+    fun photos(numberOfPhotos: Int): List<Photo> = service.findPhotos(userName, numberOfPhotos)
+}
+```
+
+------
+
+We have examples of these techniques implemented in Spring boot in the [example
+app](https://github.com/ExpediaGroup/graphql-kotlin/blob/master/examples/spring/src/main/kotlin/com/expediagroup/graphql/examples/query/NestedQueries.kt).

docs/writing-schemas/nested-queries.md

@@ -22,9 +22,12 @@ import graphql.language.StringValue
 import graphql.schema.Coercing
 import graphql.schema.GraphQLScalarType
 import graphql.schema.GraphQLType
+import org.springframework.beans.factory.BeanFactoryAware
 import reactor.core.publisher.Mono
 import java.util.UUID
+import kotlin.reflect.KClass
 import kotlin.reflect.KType
+import kotlin.reflect.full.isSubclassOf
 
 /**
  * Schema generator hook that adds additional scalar types.
@@ -46,6 +49,16 @@ class CustomSchemaGeneratorHooks(override val wiringFactory: KotlinDirectiveWiri
         Mono::class -> type.arguments.firstOrNull()?.type
         else -> type
     } ?: type
+
+    /**
+     * Exclude the Spring bean factory interface
+     */
+    override fun isValidSuperclass(kClass: KClass<*>): Boolean {
+        return when {
+            kClass.isSubclassOf(BeanFactoryAware::class) -> false
+            else -> super.isValidSuperclass(kClass)
+        }
+    }
 }
 
 internal val graphqlUUIDType = GraphQLScalarType.newScalar()

examples/spring/src/main/kotlin/com/expediagroup/graphql/examples/hooks/CustomSchemaGeneratorHooks.kt

@@ -0,0 +1,92 @@
+/*
+ * Copyright 2020 Expedia, Inc
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.expediagroup.graphql.examples.query
+
+import com.expediagroup.graphql.annotations.GraphQLIgnore
+import com.expediagroup.graphql.spring.operations.Query
+import org.springframework.beans.factory.BeanFactory
+import org.springframework.beans.factory.BeanFactoryAware
+import org.springframework.beans.factory.annotation.Autowired
+import org.springframework.context.annotation.Scope
+import org.springframework.stereotype.Component
+import org.springframework.stereotype.Service
+import kotlin.random.Random
+
+/**
+ * This is the top level query
+ */
+@Component
+class TopLevelBeanFactoryQuery : Query, BeanFactoryAware {
+
+    private lateinit var beanFactory: BeanFactory
+
+    @GraphQLIgnore
+    override fun setBeanFactory(beanFactory: BeanFactory) {
+        this.beanFactory = beanFactory
+    }
+
+    fun topLevelBeanFactory(topLevelValue: String): SecondLevelBeanFactoryQuery = beanFactory.getBean(SecondLevelBeanFactoryQuery::class.java, topLevelValue)
+}
+
+/**
+ * This is the second level object that is created at execution time of the
+ * [TopLevelBeanFactoryQuery.topLevelBeanFactory] function.
+ */
+@Component
+@Scope("prototype")
+class SecondLevelBeanFactoryQuery
+    @Autowired(required = false)
+    constructor(internal val topLevelValue: String) : BeanFactoryAware {
+
+    private lateinit var beanFactory: BeanFactory
+
+    @GraphQLIgnore
+    override fun setBeanFactory(beanFactory: BeanFactory) {
+        this.beanFactory = beanFactory
+    }
+
+    fun secondLevel(secondLevelValue: String): ThirdLevelBeanFactoryQuery = beanFactory.getBean(ThirdLevelBeanFactoryQuery::class.java, topLevelValue, secondLevelValue)
+}
+
+/**
+ * This is the third level object that is created at execution time of the
+ * [SecondLevelBeanFactoryQuery.secondLevel] function.
+ */
+@Component
+@Scope("prototype")
+class ThirdLevelBeanFactoryQuery
+    @Autowired(required = false)
+    constructor(
+        internal val topLevelValue: String,
+        internal val secondLevelValue: String
+    ) {
+
+    @Autowired
+    private lateinit var service: ExampleExternalService
+
+    fun printMessage(thirdLevelValue: String): String =
+        "topLevelValue=$topLevelValue, secondLevelValue=$secondLevelValue, thirdLevelValue=$thirdLevelValue, serviceValue=${service.getData()}"
+}
+
+/**
+ * Spring service that represents some other component that is not
+ * created from the bean factory
+ */
+@Service
+class ExampleExternalService {
+    fun getData(): Int = Random.nextInt()
+}

examples/spring/src/main/kotlin/com/expediagroup/graphql/examples/query/TopLevelBeanFactoryQuery.kt

@@ -17,7 +17,7 @@
           "writing-schemas/lists",
           "writing-schemas/interfaces",
           "writing-schemas/unions",
-          "writing-schemas/nested-queries",
+          "writing-schemas/nested-fields",
           "writing-schemas/annotations"
         ]
       },