fixes #2048

app/models/post.rb

@@ -433,7 +433,7 @@ class Post < ActiveRecord::Base
 
     def filter_metatags(tags)
       @pre_metatags, tags = tags.partition {|x| x =~ /\A(?:rating|parent):/i}
-      @post_metatags, tags = tags.partition {|x| x =~ /\A(?:-pool|pool|newpool|fav):/i}
+      @post_metatags, tags = tags.partition {|x| x =~ /\A(?:-pool|pool|newpool|fav|child):/i}
       apply_pre_metatags
       return tags
     end
@@ -468,6 +468,11 @@ class Post < ActiveRecord::Base
 
         when /^fav:(.+)$/i
           add_favorite!(CurrentUser.user)
+
+        when /^child:(.+)$/i
+          child = Post.find($1)
+          child.parent_id = id
+          child.save
         end
       end
     end

test/unit/post_test.rb

@@ -576,6 +576,20 @@ class PostTest < ActiveSupport::TestCase
             assert_equal("fav:#{@user.id}", @post.fav_string)
           end
         end
+
+        context "for a child" do
+          setup do
+            @child = FactoryGirl.create(:post)
+          end
+
+          should "update the parent relationships for both posts" do
+            @post.update_attributes(:tag_string => "aaa child:#{@child.id}")
+            @post.reload
+            @child.reload
+            assert_equal(@post.id, @child.parent_id)
+            assert(@post.has_children?)
+          end
+        end
       end
 
       context "tagged with a negated tag" do