stage3-stage4.patch

diff --git a/queries/stage4.graphql b/queries/stage4.graphql
new file mode 100644
index 0000000..b18e630
--- /dev/null
+++ b/queries/stage4.graphql
@@ -0,0 +1,17 @@
+query stage4{
+
+    allCategories { # 250
+        name
+        products { #30
+            name
+            description
+            picture(size: 100){
+                url
+            }
+            categories { #30
+                name
+            }
+        }
+    }
+
+}
diff --git a/src/main/scala/GraphQLServer.scala b/src/main/scala/GraphQLServer.scala
index 714005e..c936e20 100644
--- a/src/main/scala/GraphQLServer.scala
+++ b/src/main/scala/GraphQLServer.scala
@@ -15,6 +15,14 @@ object GraphQLServer {
 
   val repository = ShopRepository.createDatabase()
 
+  case object TooComplexQuery extends Exception
+
+  val rejectComplexQueries = QueryReducer.rejectComplexQueries(300, (_: Double, _:ShopRepository) => TooComplexQuery)
+
+  val exceptionHandler: Executor.ExceptionHandler = {
+    case (_, TooComplexQuery) => HandledException("Too complex query. Please reduce the field selection")
+  }
+
   def endpoint(requestJSON: JsValue)(implicit e: ExecutionContext): Route = {
 
     val JsObject(fields) = requestJSON
@@ -46,7 +54,9 @@ object GraphQLServer {
       repository,
       variables = vars,
       operationName = op,
-      deferredResolver = SchemaDef.deferredResolver
+      deferredResolver = SchemaDef.deferredResolver,
+      exceptionHandler = exceptionHandler,
+      queryReducers = rejectComplexQueries :: Nil
     ).map(OK -> _)
       .recover {
         case error: QueryAnalysisError => BadRequest -> error.resolveError
diff --git a/src/main/scala/SchemaDef.scala b/src/main/scala/SchemaDef.scala
index 636b2e0..1604f31 100644
--- a/src/main/scala/SchemaDef.scala
+++ b/src/main/scala/SchemaDef.scala
@@ -7,10 +7,8 @@ object SchemaDef {
   import sangria.macros.derive._
 
   //category has relation to product
-  //category id's type is String
   val product = Relation[Product, (Seq[CategoryId], Product), CategoryId]("product-category", _._1, _._2)
   //product has relation to category
-  //product id's type is Int
   val category = Relation[Category, (Seq[ProductId], Category), ProductId]("category-product", _._1, _._2)
 
   val IdentifiableType = InterfaceType(
@@ -27,6 +25,7 @@ object SchemaDef {
       IncludeMethods("picture"), //by defaul macro cosinders fields only
       AddFields(
         Field("categories", ListType(CategoryType),
+          complexity = constantComplexity(30),
           resolve = c => categoriesFetcher.deferRelSeq(category, c.value.id))
       )
     )
@@ -46,6 +45,7 @@ object SchemaDef {
       ObjectTypeDescription("The category of products"),
       AddFields(
         Field("products", ListType(ProductType),
+          complexity = constantComplexity(30),
           resolve = c => productsFetcher.deferRelSeq(product, c.value.id))
       )
     )
@@ -67,6 +67,7 @@ object SchemaDef {
     fields[ShopRepository, Unit](
       Field("allProducts", ListType(ProductType),
         description = Some("Returns a list of all available products."),
+        complexity = constantComplexity(100),
         resolve = _.ctx.allProducts
       ),
       Field("product", OptionType(ProductType),
@@ -85,14 +86,19 @@ object SchemaDef {
       Field("categories", ListType(CategoryType),
         description = Some("Returns categories by provided ids"),
         arguments = Argument("ids", ListInputType(IntType)) :: Nil,
+        complexity = constantComplexity(30),
         resolve = c => categoriesFetcher.deferSeqOpt(c.arg[List[CategoryId]]("ids"))
       ),
       Field("allCategories", ListType(CategoryType),
         description = Some("Returns a list of all available categories."),
+        complexity = constantComplexity(250),
         resolve = _.ctx.allCategories
       )
     )
   )
 
   val ShopSchema = Schema(QueryType) //define entry point
+
+  def constantComplexity[Ctx](complexity: Double) =
+    Some((_: Ctx, _: Args, child: Double) ⇒ child + complexity)
 }