From 87e98c1516311c8d06de16dae7377413a5627ad0 Mon Sep 17 00:00:00 2001
From: Alvaro Aleman <alvaroaleman@users.noreply.github.com>
Date: Wed, 5 Aug 2020 20:59:01 -0400
Subject: [PATCH] :sparkles: Add handler.FromMapFunc to simplify creation of
 custom mappers

---
 pkg/handler/enqueue_mapped.go | 16 ++++++++++++++++
 pkg/handler/eventhandler.go   |  2 +-
 pkg/handler/example_test.go   | 27 +++++++++++++--------------
 3 files changed, 30 insertions(+), 15 deletions(-)

diff --git a/pkg/handler/enqueue_mapped.go b/pkg/handler/enqueue_mapped.go
index a60790242c..6bfe44f781 100644
--- a/pkg/handler/enqueue_mapped.go
+++ b/pkg/handler/enqueue_mapped.go
@@ -25,6 +25,22 @@ import (
 	"sigs.k8s.io/controller-runtime/pkg/runtime/inject"
 )
 
+// FromMapFunc enqueues Requests by running a transformation function that outputs a collection
+// of reconcile.Requests on each Event.  The reconcile.Requests may be for an arbitrary set of objects
+// defined by some user specified transformation of the source Event.  (e.g. trigger Reconciler for a set of objects
+// in response to a cluster resize event caused by adding or deleting a Node)
+//
+// FromMapFunc is frequently used to fan-out updates from one object to one or more other
+// objects of a differing type.
+//
+// For UpdateEvents which contain both a new and old object, the transformation function is run on both
+// objects and both sets of Requests are enqueue.
+func FromMapFunc(mapFN func(MapObject) []reconcile.Request) EventHandler {
+	return &EnqueueRequestsFromMapFunc{
+		ToRequests: ToRequestsFunc(mapFN),
+	}
+}
+
 var _ EventHandler = &EnqueueRequestsFromMapFunc{}
 
 // EnqueueRequestsFromMapFunc enqueues Requests by running a transformation function that outputs a collection
diff --git a/pkg/handler/eventhandler.go b/pkg/handler/eventhandler.go
index c9b93f8b97..5970e7724c 100644
--- a/pkg/handler/eventhandler.go
+++ b/pkg/handler/eventhandler.go
@@ -33,7 +33,7 @@ import (
 // * Use EnqueueRequestForOwner to reconcile the owner of the object the event is for
 // - do this for events for the types the Controller creates.  (e.g. ReplicaSets created by a Deployment Controller)
 //
-// * Use EnqueueRequestsFromMapFunc to transform an event for an object to a reconcile of an object
+// * Use EnqueueRequestsFromMapFunc or FromMapFunc to transform an event for an object to a reconcile of an object
 // of a different type - do this for events for types the Controller may be interested in, but doesn't create.
 // (e.g. If Foo responds to cluster size events, map Node events to Foo objects.)
 //
diff --git a/pkg/handler/example_test.go b/pkg/handler/example_test.go
index 7ead7632cb..77be76c532 100644
--- a/pkg/handler/example_test.go
+++ b/pkg/handler/example_test.go
@@ -65,20 +65,19 @@ func ExampleEnqueueRequestsFromMapFunc() {
 	// controller is a controller.controller
 	err := c.Watch(
 		&source.Kind{Type: &appsv1.Deployment{}},
-		&handler.EnqueueRequestsFromMapFunc{
-			ToRequests: handler.ToRequestsFunc(func(a handler.MapObject) []reconcile.Request {
-				return []reconcile.Request{
-					{NamespacedName: types.NamespacedName{
-						Name:      a.Meta.GetName() + "-1",
-						Namespace: a.Meta.GetNamespace(),
-					}},
-					{NamespacedName: types.NamespacedName{
-						Name:      a.Meta.GetName() + "-2",
-						Namespace: a.Meta.GetNamespace(),
-					}},
-				}
-			}),
-		})
+		handler.FromMapFunc(func(a handler.MapObject) []reconcile.Request {
+			return []reconcile.Request{
+				{NamespacedName: types.NamespacedName{
+					Name:      a.Meta.GetName() + "-1",
+					Namespace: a.Meta.GetNamespace(),
+				}},
+				{NamespacedName: types.NamespacedName{
+					Name:      a.Meta.GetName() + "-2",
+					Namespace: a.Meta.GetNamespace(),
+				}},
+			}
+		}),
+	)
 	if err != nil {
 		// handle it
 	}