Handle re-ranking failure by aborting the save with error

Rely on ActiveRecord.version. Is in support AR versions

see e.g.
https://github.com/rails/rails/blob/4-0-stable/activerecord/lib/active_record/version.rb

lib/ranked-model.rb

@@ -25,14 +25,49 @@ def self.included base
       }
     end
 
+    rails_version = ActiveRecord.version.to_s
+    if rails_version < '5.0'
+      base.module_eval <<-EOS.strip_heredoc, __FILE__, __LINE__ + 1
+        def handle_ranking_return_value(return_value)
+          @ranked_model_ranking_succeeded
+        end
+
+        def abort_handle_ranking
+          nil
+        end
+      EOS
+    end
   end
 
   private
 
   def handle_ranking
-    self.class.rankers.each do |ranker|
-      ranker.with(self).handle_ranking
+    @ranked_model_ranking_succeeded = true
+    return_value = self.class.rankers.each do |ranker|
+      ranking_failed_reason = catch :ranking_failed do
+        ranker.with(self).handle_ranking
+        nil
+      end
+      handle_ranking_failure(ranker, ranking_failed_reason)
     end
+    handle_ranking_return_value(return_value)
+  end
+
+  def handle_ranking_failure(ranker, ranking_failed_reason)
+    return if ranking_failed_reason.nil?
+    errors.add ranker.column, ranking_failed_reason
+    @ranked_model_ranking_succeeded = false
+    abort_handle_ranking
+  end
+
+  # May be overriden
+  def handle_ranking_return_value(return_value)
+    return_value
+  end
+
+  # May be overriden
+  def abort_handle_ranking
+    throw :abort
   end
 
   module ClassMethods

lib/ranked-model/ranker.rb

@@ -185,10 +185,10 @@ def rearrange_ranks
         _scope = finder
         escaped_column = instance_class.ranker_connection_class.connection.quote_column_name ranker.column
         if current_first.nil?
-          return if handle_cannot_rearrange_ranks("current_first is nil").nil?
+          return if handle_cannot_rearrange_ranks("current_first not found").nil?
         end
         if current_last.nil?
-          return if handle_cannot_rearrange_ranks("current_last is nil").nil?
+          return if handle_cannot_rearrange_ranks("current_last not found").nil?
         end
         # If there is room at the bottom of the list and we're added to the very top of the list...
         if current_first.rank && current_first.rank > RankedModel::MIN_RANK_VALUE && rank == RankedModel::MAX_RANK_VALUE
@@ -215,8 +215,7 @@ def rearrange_ranks
       end
 
       def handle_cannot_rearrange_ranks(message)
-        logger.warn "[RANKED_MODEL] #{message}. Skipping re-ranking of #{instance.model_name.name} #{instance.id}"
-        nil
+        throw :ranking_failed, "Could not re-rank: #{message}."
       end
 
       def rebalance_ranks