From afb269db24ede13f93531168d3136afa6e1b18db Mon Sep 17 00:00:00 2001
From: Tim Kretschmer <tim@krtschmr.de>
Date: Wed, 27 Jan 2021 12:17:12 +0100
Subject: [PATCH] add :child_order to .rebuild! in order to respect a certain
 children order when calling rebuild! the children will be reordered with
 whatever the argument of `child_order` was

---
 README.md                                       | 2 ++
 lib/closure_tree/hierarchy_maintenance.rb       | 8 ++++----
 spec/closure_tree/hierarchy_maintenance_spec.rb | 9 +++++++++
 3 files changed, 15 insertions(+), 4 deletions(-)

diff --git a/README.md b/README.md
index 5250bdc9..c1567973 100644
--- a/README.md
+++ b/README.md
@@ -404,6 +404,8 @@ end
 ```
 This way, the complete hierarchy including all subclasses will be rebuilt.
 
+If you need to preserve a certain children order to rebuild your tree you can call `rebuild` with the keyword `child_order` and give a regular ordering hash: `rebuild!(child_order: {name: :desc})`
+
 ## Deterministic ordering
 
 By default, children will be ordered by your database engine, which may not be what you want.
diff --git a/lib/closure_tree/hierarchy_maintenance.rb b/lib/closure_tree/hierarchy_maintenance.rb
index 3023b247..acc56714 100644
--- a/lib/closure_tree/hierarchy_maintenance.rb
+++ b/lib/closure_tree/hierarchy_maintenance.rb
@@ -62,7 +62,7 @@ def _ct_before_destroy
       true # don't prevent destruction
     end
 
-    def rebuild!(called_by_rebuild = false)
+    def rebuild!(called_by_rebuild = false, child_order: nil)
       _ct.with_advisory_lock do
         delete_hierarchy_references unless (defined? @was_new_record) && @was_new_record
         hierarchy_class.create!(:ancestor => self, :descendant => self, :generations => 0)
@@ -82,7 +82,7 @@ def rebuild!(called_by_rebuild = false)
           _ct_reorder_siblings if !called_by_rebuild
         end
 
-        children.find_each { |c| c.rebuild!(true) }
+        children.reorder(child_order).find_each { |c| c.rebuild!(true, child_order: child_order) }
 
         _ct_reorder_children if _ct.order_is_numeric? && children.present?
       end
@@ -110,10 +110,10 @@ def delete_hierarchy_references
     module ClassMethods
       # Rebuilds the hierarchy table based on the parent_id column in the database.
       # Note that the hierarchy table will be truncated.
-      def rebuild!
+      def rebuild!(child_order: nil)
         _ct.with_advisory_lock do
           cleanup!
-          roots.find_each { |n| n.send(:rebuild!) } # roots just uses the parent_id column, so this is safe.
+          roots.find_each { |n| n.send(:rebuild!, child_order: child_order) } # roots just uses the parent_id column, so this is safe.
         end
         nil
       end
diff --git a/spec/closure_tree/hierarchy_maintenance_spec.rb b/spec/closure_tree/hierarchy_maintenance_spec.rb
index a4ad09f5..321391b4 100644
--- a/spec/closure_tree/hierarchy_maintenance_spec.rb
+++ b/spec/closure_tree/hierarchy_maintenance_spec.rb
@@ -12,6 +12,15 @@
       Metal.rebuild!
       expect(MetalHierarchy.count).to eq(hierarchy_count)
     end
+
+    it 'rebuild tree with specific child order' do
+      parent = Metal.create(value: "Parent")
+      Metal.create(value: "name3")
+      Metal.create(value: "name1")
+      Metal.create(value: "name2")
+      expect(parent.children).to receive(:reorder).with({value: :desc}).once.and_call_original
+      parent.rebuild!(child_order: {value: :desc})
+    end
   end
 
   describe '.cleanup!' do