Rails 6.1 Compatability

Gemfile

@@ -4,7 +4,7 @@ source 'https://rubygems.org'
 gemspec
 
 gem 'pg', '>= 0.21', '< 1.3'
-gem 'activerecord', '>= 5.0', '< 6.1'
+gem 'activerecord', '>= 5.0', '< 6.2'
 
 group :local do
   gem 'yard'

activerecord-hierarchical_query.gemspec

@@ -16,10 +16,10 @@ Gem::Specification.new do |spec|
   spec.test_files    = spec.files.grep(%r{^(test|spec|features)/})
   spec.require_paths = %w(lib)
 
-  spec.add_dependency 'activerecord', '>= 5.0', '< 6.1'
+  spec.add_dependency 'activerecord', '>= 5.0', '< 6.2'
   spec.add_dependency 'pg', '>= 0.21', '< 1.3'
 
-  spec.add_development_dependency 'bundler', '~> 1.16'
+  spec.add_development_dependency 'bundler', '>= 1.16'
   spec.add_development_dependency 'rake', '~> 12.3'
   spec.add_development_dependency 'rspec', '~> 3.8'
   spec.add_development_dependency 'database_cleaner', '~> 1.7'

gemfiles/rails6.1.0.gemfile

@@ -0,0 +1,23 @@
+# This file was generated by Appraisal
+
+source "https://rubygems.org"
+
+gem "pg", ">= 0.21", "< 1.2"
+gem "activerecord", "~> 6.1.0.rc1"
+
+group :local do
+  gem "yard"
+  gem "redcarpet"
+  gem "github-markup"
+  gem "appraisal", ">= 1.0.0"
+end
+
+group :development do
+  gem "pry"
+end
+
+group :travis do
+  gem "coveralls", "~> 0.8.21"
+end
+
+gemspec path: "../"

lib/active_record/hierarchical_query/cte/columns.rb

@@ -1,5 +1,3 @@
-require 'arel/visitors/depth_first'
-
 module ActiveRecord
   module HierarchicalQuery
     module CTE
@@ -18,7 +16,23 @@ def to_a
 
         private
         def connect_by_columns
-          @query.join_conditions.grep(Arel::Attributes::Attribute) { |column| column.name.to_s }
+          columns = []
+          traverse(@query.join_conditions) do |node|
+            columns << node.name.to_s if node.is_a?(Arel::Attributes::Attribute)
+          end
+          columns
+        end
+
+        def traverse(ast, &blck)
+          if ast && ast.respond_to?(:left) && ast.left
+            traverse(ast.left, &blck)
+          end
+
+          if ast && ast.respond_to?(:right) && ast.right
+            traverse(ast.right, &blck)
+          end
+
+          yield ast
         end
       end
     end