update

src/main/kotlin/Payload.kt

@@ -0,0 +1,6 @@
+data class WipeDataPayload(val success: Boolean) {
+  companion object {
+    val SUCCESS = WipeDataPayload(true)
+    val FAILURE = WipeDataPayload(false)
+  }
+}

src/main/kotlin/PersonRepository.kt

@@ -1,6 +1,8 @@
 object PersonRepository {
   var people: MutableList<Person> = mutableListOf()
 
+  fun clear() = people.clear()
+
   fun addPerson(name: String): Person {
     val id = nextId()
     val person = Person(id, name, emptyList())
@@ -17,7 +19,9 @@ object PersonRepository {
   fun addFriends(first: Person, second: Person): Boolean =
     first.addFriend(second) && second.addFriend(first)
 
-  fun allPeople() = people.toList()
+  fun allPeople() = people.toList().also {
+    println("Expensive call to get all people")
+  }
 
   // Note: this can be expensive, so look at the Person.kt class for a hint on how to batch calls
   fun findById(id: Int) = people.first { it.id == id }

src/main/kotlin/PetsRepository.kt

@@ -1,10 +1,14 @@
 object PetsRepository {
   var pets = mutableListOf<Pet>()
 
+  fun clear() = pets.clear()
+
   fun findById(id: Int) = pets.first { it.id == id }
-  fun findByIds(ids: List<Int>) = pets.filter { it.id in ids}.also {
-    println("Another expensive call to get pets with ids: $ids")
-  }
+  fun findByIds(ids: List<Int>) = pets
+    .filter { it.id in ids}
+    .also {
+      println("Another expensive call to get pets with ids: $ids")
+    }
 
   fun allPets() = pets.toList()
 

src/main/kotlin/schema.kt

@@ -40,9 +40,19 @@ class QueryResolver : GraphQLQueryResolver {
 
 @Suppress("unused") // GraphQL by reflection
 class MutationResolver : GraphQLMutationResolver {
+  fun wipeData() = run {
+    try {
+      PersonRepository.clear()
+      PetsRepository.clear()
+      WipeDataPayload.SUCCESS
+    } catch (e: Exception) {
+      WipeDataPayload.FAILURE
+    }
+  }
+
   fun generateData(): List<Person> {
     val faker = Faker()
-    val newPeople = (1..2).map {
+    val newPeople = (1..10).map {
       val fakePersonName = faker.name().nameWithMiddle()
 
       val petIds = (0..Random.nextInt(5)).map {

src/main/resources/schema.graphql

@@ -51,6 +51,11 @@ type Mutation {
   addPerson(input: PersonInput!): Person!
   addFriends(input: AddFriendsInput!): Boolean!
   generateData: [Person!]!
+  wipeData: WipeDataPayload!
+}
+
+type WipeDataPayload {
+  success: Boolean!
 }
 
 # RFC3339: full-date