diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 7704685..8a7c089 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -50,16 +50,16 @@ jobs:
           - activerecord_6.1
           - activerecord_edge
         adapter:
-          - 'sqlite3:///:memory:'
+          - sqlite3:///tmp/closure_tree_test
           - mysql2://root:root@0/closure_tree_test
-          - postgres://closure_tree:closure_tree@0/closure_tree_test
+          - postgres://postgres:postgres@0/closure_tree_test
         exclude:
           - ruby: '3.0'
             rails: activerecord_edge
 
     steps:
       - name: Checkout
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
 
       - name: Setup Ruby
         uses: ruby/setup-ruby@v1
@@ -74,7 +74,8 @@ jobs:
       - name: RSpec
         env:
           RAILS_VERSION: ${{ matrix.rails }}
-          DB_ADAPTER: ${{ matrix.adapter }}
+          DATABASE_URL: ${{ matrix.adapter }}
+          SECONDARY_DATABASE_URL: ${{ matrix.adapter }}_secondary
           BUNDLE_GEMFILE: gemfiles/${{ matrix.rails }}.gemfile
           WITH_ADVISORY_LOCK_PREFIX: ${{ github.run_id }}
         run: bin/rake
diff --git a/.github/workflows/ci_jruby.yml b/.github/workflows/ci_jruby.yml
index c7d0156..558fbcc 100644
--- a/.github/workflows/ci_jruby.yml
+++ b/.github/workflows/ci_jruby.yml
@@ -43,12 +43,12 @@ jobs:
           - activerecord_7.0
           - activerecord_6.1
         adapter:
-          - 'sqlite3:///:memory:'
+          - sqlite3:///tmp/closure_tree_test
           - mysql2://root:root@0/closure_tree_test
-          - postgres://closure_tree:closure_tree@0/closure_tree_test
+          - postgres://postgres:postgres@0/closure_tree_test
     steps:
       - name: Checkout
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
 
       - name: Setup Ruby
         uses: ruby/setup-ruby@v1
@@ -63,7 +63,8 @@ jobs:
       - name: RSpec
         env:
           RAILS_VERSION: ${{ matrix.rails }}
-          DB_ADAPTER: ${{ matrix.adapter }}
+          DATABASE_URL: ${{ matrix.adapter }}
+          SECONDARY_DATABASE_URL: ${{ matrix.adapter }}_secondary
           BUNDLE_GEMFILE: gemfiles/${{ matrix.rails }}.gemfile
           WITH_ADVISORY_LOCK_PREFIX: ${{ github.run_id }}
         run: bin/rake
diff --git a/.github/workflows/ci_truffleruby.yml b/.github/workflows/ci_truffleruby.yml
index b61630f..77bf270 100644
--- a/.github/workflows/ci_truffleruby.yml
+++ b/.github/workflows/ci_truffleruby.yml
@@ -45,13 +45,13 @@ jobs:
           - activerecord_7.0
           - activerecord_6.1
         adapter:
-          - 'sqlite3:///:memory:'
+          - sqlite3:///tmp/closure_tree_test
           - mysql2://root:root@0/closure_tree_test
-          - postgres://closure_tree:closure_tree@0/closure_tree_test
+          - postgres://postgres:postgres@0/closure_tree_test
 
     steps:
       - name: Checkout
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
 
       - name: Setup Ruby
         uses: ruby/setup-ruby@v1
@@ -66,7 +66,8 @@ jobs:
       - name: RSpec
         env:
           RAILS_VERSION: ${{ matrix.rails }}
-          DB_ADAPTER: ${{ matrix.adapter }}
+          DATABASE_URL: ${{ matrix.adapter }}
+          SECONDARY_DATABASE_URL: ${{ matrix.adapter }}_secondary
           BUNDLE_GEMFILE: gemfiles/${{ matrix.rails }}.gemfile
           WITH_ADVISORY_LOCK_PREFIX: ${{ github.run_id }}
         run: bin/rake
diff --git a/.gitignore b/.gitignore
index 2f6900c..e9f555f 100644
--- a/.gitignore
+++ b/.gitignore
@@ -14,3 +14,4 @@ tmp/
 .ruby-*
 *.iml
 coverage/
+.env
diff --git a/lib/closure_tree/has_closure_tree.rb b/lib/closure_tree/has_closure_tree.rb
index b0bc5b1..a45462c 100644
--- a/lib/closure_tree/has_closure_tree.rb
+++ b/lib/closure_tree/has_closure_tree.rb
@@ -31,10 +31,6 @@ def has_closure_tree(options = {})
 
       include ClosureTree::DeterministicOrdering if _ct.order_option?
       include ClosureTree::NumericDeterministicOrdering if _ct.order_is_numeric?
-
-      connection_pool.release_connection
-    rescue StandardError => e
-      raise e unless ClosureTree.configuration.database_less
     end
 
     alias_method :acts_as_tree, :has_closure_tree
diff --git a/lib/closure_tree/has_closure_tree_root.rb b/lib/closure_tree/has_closure_tree_root.rb
index 70e327d..26f9d53 100644
--- a/lib/closure_tree/has_closure_tree_root.rb
+++ b/lib/closure_tree/has_closure_tree_root.rb
@@ -77,8 +77,6 @@ def has_closure_tree_root(assoc_name, options = {})
 
         @closure_tree_roots[assoc_name][assoc_map] = root
       end
-
-      connection_pool.release_connection
     end
   end
 end
diff --git a/lib/closure_tree/numeric_order_support.rb b/lib/closure_tree/numeric_order_support.rb
index 0223a41..351720a 100644
--- a/lib/closure_tree/numeric_order_support.rb
+++ b/lib/closure_tree/numeric_order_support.rb
@@ -1,53 +1,42 @@
 module ClosureTree
   module NumericOrderSupport
-
-    def self.adapter_for_connection(connection)
-      das = WithAdvisoryLock::DatabaseAdapterSupport.new(connection)
-      if das.postgresql?
-        ::ClosureTree::NumericOrderSupport::PostgreSQLAdapter
-      elsif das.mysql?
-        ::ClosureTree::NumericOrderSupport::MysqlAdapter
-      else
-        ::ClosureTree::NumericOrderSupport::GenericAdapter
-      end
-    end
-
     module MysqlAdapter
-      def reorder_with_parent_id(parent_id, minimum_sort_order_value = nil)
-        return if parent_id.nil? && dont_order_roots
+      module_function def reorder_with_parent_id(ct, parent_id, minimum_sort_order_value = nil)
+        return if parent_id.nil? && ct.dont_order_roots
+
         min_where = if minimum_sort_order_value
-          "AND #{quoted_order_column} >= #{minimum_sort_order_value}"
+          "AND #{ct.quoted_order_column} >= #{minimum_sort_order_value}"
         else
           ""
         end
-        connection.execute 'SET @i = 0'
-        connection.execute <<-SQL.squish
-          UPDATE #{quoted_table_name}
-            SET #{quoted_order_column} = (@i := @i + 1) + #{minimum_sort_order_value.to_i - 1}
-          WHERE #{where_eq(parent_column_name, parent_id)} #{min_where}
-          ORDER BY #{nulls_last_order_by}
+        ct.connection.execute 'SET @i = 0'
+        ct.connection.execute <<-SQL.squish
+          UPDATE #{ct.quoted_table_name}
+            SET #{ct.quoted_order_column} = (@i := @i + 1) + #{minimum_sort_order_value.to_i - 1}
+          WHERE #{ct.where_eq(ct.parent_column_name, parent_id)} #{min_where}
+          ORDER BY #{ct.nulls_last_order_by}
         SQL
       end
     end
 
     module PostgreSQLAdapter
-      def reorder_with_parent_id(parent_id, minimum_sort_order_value = nil)
-        return if parent_id.nil? && dont_order_roots
+      module_function def reorder_with_parent_id(ct, parent_id, minimum_sort_order_value = nil)
+        return if parent_id.nil? && ct.dont_order_roots
         min_where = if minimum_sort_order_value
-          "AND #{quoted_order_column} >= #{minimum_sort_order_value}"
+          "AND #{ct.quoted_order_column} >= #{minimum_sort_order_value}"
         else
           ""
         end
-        connection.execute <<-SQL.squish
-          UPDATE #{quoted_table_name}
-          SET #{quoted_order_column(false)} = t.seq + #{minimum_sort_order_value.to_i - 1}
+        ct.connection.execute <<-SQL.squish
+          UPDATE #{ct.quoted_table_name}
+          SET #{ct.quoted_order_column(false)} = t.seq + #{minimum_sort_order_value.to_i - 1}
           FROM (
-            SELECT #{quoted_id_column_name} AS id, row_number() OVER(ORDER BY #{order_by}) AS seq
-            FROM #{quoted_table_name}
-            WHERE #{where_eq(parent_column_name, parent_id)} #{min_where}
+            SELECT #{ct.quoted_id_column_name} AS id, row_number() OVER(ORDER BY #{ct.order_by}) AS seq
+            FROM #{ct.quoted_table_name}
+            WHERE #{ct.where_eq(ct.parent_column_name, parent_id)} #{min_where}
           ) AS t
-          WHERE #{quoted_table_name}.#{quoted_id_column_name} = t.id and
-                #{quoted_table_name}.#{quoted_order_column(false)} is distinct from t.seq + #{minimum_sort_order_value.to_i - 1}
+          WHERE #{ct.quoted_table_name}.#{ct.quoted_id_column_name} = t.id and
+                #{ct.quoted_table_name}.#{ct.quoted_order_column(false)} is distinct from t.seq + #{minimum_sort_order_value.to_i - 1}
         SQL
       end
 
@@ -57,18 +46,31 @@ def rows_updated(result)
     end
 
     module GenericAdapter
-      def reorder_with_parent_id(parent_id, minimum_sort_order_value = nil)
-        return if parent_id.nil? && dont_order_roots
-        scope = model_class.
-          where(parent_column_sym => parent_id).
-          order(nulls_last_order_by)
+      module_function def reorder_with_parent_id(ct, parent_id, minimum_sort_order_value = nil)
+        return if parent_id.nil? && ct.dont_order_roots
+        binding.irb
+        scope = ct.
+          where(ct.parent_column_sym => parent_id).
+          order(ct.nulls_last_order_by)
         if minimum_sort_order_value
-          scope = scope.where("#{quoted_order_column} >= #{minimum_sort_order_value}")
+          scope = scope.where("#{ct.quoted_order_column} >= #{minimum_sort_order_value}")
         end
         scope.each_with_index do |ea, idx|
           ea.update_order_value(idx + minimum_sort_order_value.to_i)
         end
       end
     end
+
+
+    module_function def adapter_for_connection(ct, parent_id, minimum_sort_order_value = nil)
+      das = WithAdvisoryLock::DatabaseAdapterSupport.new(ct.connection)
+      if das.postgresql?
+        PostgreSQLAdapter.reorder_with_parent_id(ct, parent_id, minimum_sort_order_value = nil)
+      elsif das.mysql?
+        MysqlAdapter.reorder_with_parent_id(ct, parent_id, minimum_sort_order_value = nil)
+      else
+        GenericAdapter.reorder_with_parent_id(ct, parent_id, minimum_sort_order_value = nil)
+      end
+    end
   end
 end
diff --git a/lib/closure_tree/support.rb b/lib/closure_tree/support.rb
index e887090..0e406bd 100644
--- a/lib/closure_tree/support.rb
+++ b/lib/closure_tree/support.rb
@@ -26,9 +26,6 @@ def initialize(model_class, options)
         :numeric_order => false
       }.merge(options)
       raise ArgumentError, "name_column can't be 'path'" if options[:name_column] == 'path'
-      if order_is_numeric?
-        extend NumericOrderSupport.adapter_for_connection(connection)
-      end
     end
 
     def hierarchy_class_for_model
@@ -54,6 +51,10 @@ def hash
       hierarchy_class
     end
 
+    def reorder_with_parent_id(parent_id, minimum_sort_order_value = nil)
+      NumericOrderSupport.adapter_for_connection(self, parent_id, minimum_sort_order_value)
+    end
+
     def hierarchy_table_name
       # We need to use the table_name, not something like ct_class.to_s.demodulize + "_hierarchies",
       # because they may have overridden the table name, which is what we want to be consistent with
diff --git a/lib/closure_tree/support_attributes.rb b/lib/closure_tree/support_attributes.rb
index 38879ad..5ec8ef4 100644
--- a/lib/closure_tree/support_attributes.rb
+++ b/lib/closure_tree/support_attributes.rb
@@ -117,7 +117,7 @@ def quoted_order_column(include_table_name = true)
 
     # table_name alias keyword , like "AS". When used on table name alias, Oracle Database don't support used 'AS'
     def t_alias_keyword
-      (ActiveRecord::Base.connection.adapter_name.to_sym == :OracleEnhanced) ? "" : "AS"
+      (connection.adapter_name.to_sym == :OracleEnhanced) ? "" : "AS"
     end
   end
 end
diff --git a/spec/spec_helper.rb b/spec/spec_helper.rb
index eba943f..1803df2 100644
--- a/spec/spec_helper.rb
+++ b/spec/spec_helper.rb
@@ -1,6 +1,5 @@
 # frozen_string_literal: true
 
-
 require 'database_cleaner'
 require 'closure_tree/test/matcher'
 require 'tmpdir'
@@ -11,6 +10,7 @@
 require 'active_record'
 require 'active_support/core_ext/array'
 
+puts "Using ActiveRecord #{ActiveRecord.gem_version} and #{RUBY_ENGINE} #{RUBY_ENGINE_VERSION} as #{RUBY_VERSION}"
 
 # Start Simplecov
 if RUBY_ENGINE == 'ruby'
@@ -20,10 +20,23 @@
   end
 end
 
+primary_database_url = ENV['DATABASE_URL'].presence || "sqlite3:///tmp/closure_tree_test"
+secondary_database_url = ENV['SECONDARY_DATABASE_URL'].presence || "sqlite3:///tmp/closure_tree_test-s"
+
+puts "Using primary database #{primary_database_url}"
+puts "Using secondary database #{secondary_database_url}"
+
 ActiveRecord::Base.configurations = {
   default_env: {
-    url: ENV.fetch('DATABASE_URL', "sqlite3::memory:"),
-    properties: { allowPublicKeyRetrieval: true } # for JRuby madness
+    primary: {
+      primary: true,
+      url: primary_database_url,
+      properties: { allowPublicKeyRetrieval: true } # for JRuby madness
+    },
+    secondary: {
+      url: secondary_database_url,
+      properties: { allowPublicKeyRetrieval: true } # for JRuby madness
+    }
   }
 }
 
@@ -31,14 +44,9 @@
 ActiveRecord::Migration.verbose = false
 ActiveRecord::Base.table_name_prefix = ENV['DB_PREFIX'].to_s
 ActiveRecord::Base.table_name_suffix = ENV['DB_SUFFIX'].to_s
-ActiveRecord::Base.establish_connection
 
 def env_db
-  @env_db ||= if ActiveRecord::Base.respond_to?(:connection_db_config)
-                ActiveRecord::Base.connection_db_config.adapter
-              else
-                ActiveRecord::Base.connection_config[:adapter]
-              end.to_sym
+  @env_db ||= ActiveRecord::Base.connection_db_config.adapter.to_sym
 end
 
 # Use in specs to skip some tests
@@ -73,15 +81,12 @@ def sqlite?
   # disable monkey patching
   # see: https://relishapp.com/rspec/rspec-core/v/3-8/docs/configuration/zero-monkey-patching-mode
   config.disable_monkey_patching!
+  config.before(:suite) do
+    ENV['FLOCK_DIR'] = Dir.mktmpdir if sqlite?
+  end
 
-  if sqlite?
-    config.before(:suite) do
-      ENV['FLOCK_DIR'] = Dir.mktmpdir
-    end
-
-    config.after(:suite) do
-      FileUtils.remove_entry_secure ENV['FLOCK_DIR']
-    end
+  config.after(:suite) do
+    FileUtils.remove_entry_secure(ENV['FLOCK_DIR']) if sqlite?
   end
 end
 
@@ -92,14 +97,12 @@ def sqlite?
 # See: https://github.com/ClosureTree/with_advisory_lock
 ENV['WITH_ADVISORY_LOCK_PREFIX'] ||= SecureRandom.hex
 
-ActiveRecord::Base.connection.recreate_database("closure_tree_test") unless sqlite?
-puts "Testing with #{env_db} database, ActiveRecord #{ActiveRecord.gem_version} and #{RUBY_ENGINE} #{RUBY_ENGINE_VERSION} as #{RUBY_VERSION}"
 # Require our gem
 require 'closure_tree'
 
 # Load test helpers
 require_relative 'support/schema'
-require_relative 'support/models'
 require_relative 'support/helpers'
 require_relative 'support/exceed_query_limit'
 require_relative 'support/query_counter'
+puts "Testing with #{env_db} database"
diff --git a/spec/support/exceed_query_limit.rb b/spec/support/exceed_query_limit.rb
index b167a82..a8d7cf9 100644
--- a/spec/support/exceed_query_limit.rb
+++ b/spec/support/exceed_query_limit.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # Derived from http://stackoverflow.com/a/13423584/153896. Updated for RSpec 3.
 RSpec::Matchers.define :exceed_query_limit do |expected|
   supports_block_expectations
@@ -6,7 +8,7 @@
     query_count(&block) > expected
   end
 
-  failure_message_when_negated do |actual|
+  failure_message_when_negated do |_actual|
     "Expected to run maximum #{expected} queries, got #{@counter.query_count}"
   end
 
diff --git a/spec/support/helpers.rb b/spec/support/helpers.rb
index 1404714..d303eba 100644
--- a/spec/support/helpers.rb
+++ b/spec/support/helpers.rb
@@ -1,7 +1,9 @@
+# frozen_string_literal: true
+
 # See http://stackoverflow.com/a/22388177/1268016
 def count_queries(&block)
   count = 0
-  counter_fn = ->(name, started, finished, unique_id, payload) do
+  counter_fn = lambda do |_name, _started, _finished, _unique_id, payload|
     count += 1 unless %w[CACHE SCHEMA].include? payload[:name]
   end
   ActiveSupport::Notifications.subscribed(counter_fn, 'sql.active_record', &block)
diff --git a/spec/support/models.rb b/spec/support/models.rb
index 9927af4..cb937a1 100644
--- a/spec/support/models.rb
+++ b/spec/support/models.rb
@@ -1,5 +1,20 @@
-class Tag < ActiveRecord::Base
-  has_closure_tree :dependent => :destroy, :order => :name
+# frozen_string_literal: true
+
+
+
+class ApplicationRecord < ActiveRecord::Base
+  self.abstract_class = true
+
+  connects_to database: { writing: :primary, reading: :primary }
+end
+
+class SecondDatabaseRecord < ActiveRecord::Base
+  self.abstract_class = true
+
+  connects_to database: { writing: :secondary, reading: :secondary }
+end
+class Tag < ApplicationRecord
+  has_closure_tree dependent: :destroy, order: :name
   before_destroy :add_destroyed_tag
 
   def to_s
@@ -8,11 +23,11 @@ def to_s
 
   def add_destroyed_tag
     # Proof for the tests that the destroy rather than the delete method was called:
-    DestroyedTag.create(:name => name)
+    DestroyedTag.create(name: to_s)
   end
 end
 
-class UUIDTag < ActiveRecord::Base
+class UUIDTag < ApplicationRecord
   self.primary_key = :uuid
   before_create :set_uuid
   has_closure_tree dependent: :destroy, order: 'name', parent_column_name: 'parent_uuid'
@@ -28,40 +43,40 @@ def to_s
 
   def add_destroyed_tag
     # Proof for the tests that the destroy rather than the delete method was called:
-    DestroyedTag.create(:name => name)
+    DestroyedTag.create(name: to_s)
   end
 end
 
-class DestroyedTag < ActiveRecord::Base
+class DestroyedTag < ApplicationRecord
 end
 
-class Group < ActiveRecord::Base
+class Group < ApplicationRecord
   has_closure_tree_root :root_user
 end
 
-class Grouping < ActiveRecord::Base
-  has_closure_tree_root :root_person, class_name: "User", foreign_key: :group_id
+class Grouping < ApplicationRecord
+  has_closure_tree_root :root_person, class_name: 'User', foreign_key: :group_id
 end
 
-class UserSet < ActiveRecord::Base
-  has_closure_tree_root :root_user, class_name: "Useur"
+class UserSet < ApplicationRecord
+  has_closure_tree_root :root_user, class_name: 'Useur'
 end
 
-class Team < ActiveRecord::Base
-  has_closure_tree_root :root_user, class_name: "User", foreign_key: :grp_id
+class Team < ApplicationRecord
+  has_closure_tree_root :root_user, class_name: 'User', foreign_key: :grp_id
 end
 
-class User < ActiveRecord::Base
-  acts_as_tree :parent_column_name => "referrer_id",
-    :name_column => 'email',
-    :hierarchy_class_name => 'ReferralHierarchy',
-    :hierarchy_table_name => 'referral_hierarchies'
+class User < ApplicationRecord
+  acts_as_tree parent_column_name: 'referrer_id',
+               name_column: 'email',
+               hierarchy_class_name: 'ReferralHierarchy',
+               hierarchy_table_name: 'referral_hierarchies'
 
   has_many :contracts, inverse_of: :user
   belongs_to :group # Can't use and don't need inverse_of here when using has_closure_tree_root.
 
   def indirect_contracts
-    Contract.where(:user_id => descendant_ids)
+    Contract.where(user_id: descendant_ids)
   end
 
   def to_s
@@ -69,21 +84,21 @@ def to_s
   end
 end
 
-class Contract < ActiveRecord::Base
+class Contract < ApplicationRecord
   belongs_to :user, inverse_of: :contracts
   belongs_to :contract_type, inverse_of: :contracts
 end
 
-class ContractType < ActiveRecord::Base
+class ContractType < ApplicationRecord
   has_many :contracts, inverse_of: :contract_type
 end
 
-class Label < ActiveRecord::Base
+class Label < ApplicationRecord
   # make sure order doesn't matter
-  acts_as_tree :order => :column_whereby_ordering_is_inferred, # <- symbol, and not "sort_order"
-    :numeric_order => true,
-    :parent_column_name => "mother_id",
-    :dependent => :destroy
+  acts_as_tree order: :column_whereby_ordering_is_inferred, # <- symbol, and not "sort_order"
+               numeric_order: true,
+               parent_column_name: 'mother_id',
+               dependent: :destroy
 
   def to_s
     "#{self.class}: #{name}"
@@ -99,13 +114,13 @@ class DateLabel < Label
 class DirectoryLabel < Label
 end
 
-class LabelWithoutRootOrdering < ActiveRecord::Base
+class LabelWithoutRootOrdering < ApplicationRecord
   # make sure order doesn't matter
-  acts_as_tree :order => :column_whereby_ordering_is_inferred, # <- symbol, and not "sort_order"
-    :numeric_order => true,
-    :dont_order_roots => true,
-    :parent_column_name => "mother_id",
-    :hierarchy_table_name => "label_hierarchies"
+  acts_as_tree order: :column_whereby_ordering_is_inferred, # <- symbol, and not "sort_order"
+               numeric_order: true,
+               dont_order_roots: true,
+               parent_column_name: 'mother_id',
+               hierarchy_table_name: 'label_hierarchies'
 
   self.table_name = "#{table_name_prefix}labels#{table_name_suffix}"
 
@@ -114,7 +129,7 @@ def to_s
   end
 end
 
-class CuisineType < ActiveRecord::Base
+class CuisineType < ApplicationRecord
   acts_as_tree
 end
 
@@ -122,12 +137,13 @@ module Namespace
   def self.table_name_prefix
     'namespace_'
   end
-  class Type < ActiveRecord::Base
+
+  class Type < ApplicationRecord
     has_closure_tree dependent: :destroy
   end
 end
 
-class Metal < ActiveRecord::Base
+class Metal < ApplicationRecord
   self.table_name = "#{table_name_prefix}metal#{table_name_suffix}"
   has_closure_tree order: 'sort_order', name_column: 'value'
   self.inheritance_column = 'metal_type'
@@ -139,6 +155,6 @@ class Adamantium < Metal
 class Unobtanium < Metal
 end
 
-class MenuItem < ActiveRecord::Base
+class MenuItem < SecondDatabaseRecord
   has_closure_tree touch: true, with_advisory_lock: false
 end
diff --git a/spec/support/query_counter.rb b/spec/support/query_counter.rb
index f36cfc0..44c9864 100644
--- a/spec/support/query_counter.rb
+++ b/spec/support/query_counter.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # From http://stackoverflow.com/a/13423584/153896
 module ActiveRecord
   class QueryCounter
@@ -11,8 +13,8 @@ def to_proc
       lambda(&method(:callback))
     end
 
-    def callback(name, start, finish, message_id, values)
-      @query_count += 1 unless %w(CACHE SCHEMA).include?(values[:name])
+    def callback(_name, _start, _finish, _message_id, values)
+      @query_count += 1 unless %w[CACHE SCHEMA].include?(values[:name])
     end
   end
 end
diff --git a/spec/support/schema.rb b/spec/support/schema.rb
index 30a4a99..95cbdf1 100644
--- a/spec/support/schema.rb
+++ b/spec/support/schema.rb
@@ -1,7 +1,21 @@
 # frozen_string_literal: true
 
+require_relative 'models'
+ApplicationRecord.establish_connection
+if sqlite?
+  ActiveRecord::Tasks::DatabaseTasks.drop(:primary, 'test')
+  ActiveRecord::Tasks::DatabaseTasks.create(:primary, 'test')
+  ActiveRecord::Tasks::DatabaseTasks.drop(:secondary, 'test')
+  ActiveRecord::Tasks::DatabaseTasks.create(:secondary, 'test')
+else
+  ActiveRecord::Tasks::DatabaseTasks.drop(:primary)
+  ActiveRecord::Tasks::DatabaseTasks.create(:primary)
+  ActiveRecord::Tasks::DatabaseTasks.drop(:secondary)
+  ActiveRecord::Tasks::DatabaseTasks.create(:secondary)
+end
+
 ActiveRecord::Schema.define(version: 0) do
-  create_table 'tags', force: :cascade do |t|
+  connection.create_table Tag.table_name, force: :cascade do |t|
     t.string 'name'
     t.string 'title'
     t.references 'parent'
@@ -9,13 +23,17 @@
     t.timestamps null: false
   end
 
-  create_table 'tag_hierarchies', id: false, force: :cascade do |t|
+  create_table Tag.hierarchy_class.table_name, id: false, force: :cascade do |t|
     t.references 'ancestor', null: false
     t.references 'descendant', null: false
     t.integer 'generations', null: false
   end
 
-  create_table 'uuid_tags', id: false, force: :cascade do |t|
+  add_index Tag.hierarchy_class.table_name, %i[ancestor_id descendant_id generations], unique: true,
+                                                                                       name: 'tag_anc_desc_idx'
+  add_index Tag.hierarchy_class.table_name, [:descendant_id], name: 'tag_desc_idx'
+
+  create_table UUIDTag.table_name, id: false, force: :cascade do |t|
     t.string 'uuid', primary_key: true
     t.string 'name'
     t.string 'title'
@@ -24,95 +42,99 @@
     t.timestamps null: false
   end
 
-  create_table 'uuid_tag_hierarchies', id: false, force: :cascade do |t|
+  create_table UUIDTag.hierarchy_class.table_name, id: false, force: :cascade do |t|
     t.string 'ancestor_id', null: false
     t.string 'descendant_id', null: false
     t.integer 'generations', null: false
   end
 
-  create_table 'destroyed_tags', force: :cascade do |t|
+  create_table DestroyedTag.table_name, force: :cascade do |t|
     t.string 'name'
   end
 
-  add_index 'tag_hierarchies', %i[ancestor_id descendant_id generations], unique: true,
-                                                                          name: 'tag_anc_desc_idx'
-  add_index 'tag_hierarchies', [:descendant_id], name: 'tag_desc_idx'
-
-  create_table 'groups', force: :cascade do |t|
+  create_table Group.table_name, force: :cascade do |t|
     t.string 'name', null: false
   end
 
-  create_table 'groupings', force: :cascade do |t|
+  create_table Grouping.table_name, force: :cascade do |t|
     t.string 'name', null: false
   end
 
-  create_table 'user_sets', force: :cascade do |t|
+  create_table UserSet.table_name, force: :cascade do |t|
     t.string 'name', null: false
   end
 
-  create_table 'teams', force: :cascade do |t|
+  create_table Team.table_name, force: :cascade do |t|
     t.string 'name', null: false
   end
 
-  create_table 'users', force: :cascade do |t|
+  create_table User.table_name, force: :cascade do |t|
     t.string 'email'
     t.references 'referrer'
     t.integer 'group_id'
     t.timestamps null: false
   end
 
-  create_table 'contracts', force: :cascade do |t|
+  create_table User.hierarchy_class.table_name, id: false, force: :cascade do |t|
+    t.references 'ancestor', null: false
+    t.references 'descendant', null: false
+    t.integer 'generations', null: false
+  end
+
+  add_index User.hierarchy_class.table_name, %i[ancestor_id descendant_id generations], unique: true,
+                                                                                        name: 'ref_anc_desc_idx'
+  add_index User.hierarchy_class.table_name, [:descendant_id], name: 'ref_desc_idx'
+
+  create_table Contract.table_name, force: :cascade do |t|
     t.references 'user', null: false
     t.references 'contract_type'
     t.string 'title'
   end
 
-  create_table 'contract_types', force: :cascade do |t|
+  create_table ContractType.table_name, force: :cascade do |t|
     t.string 'name', null: false
   end
 
-  create_table 'referral_hierarchies', id: false, force: :cascade do |t|
-    t.references 'ancestor', null: false
-    t.references 'descendant', null: false
-    t.integer 'generations', null: false
-  end
-
-  create_table 'labels', force: :cascade do |t|
+  create_table Label.table_name, force: :cascade do |t|
     t.string 'name'
     t.string 'type'
     t.integer 'column_whereby_ordering_is_inferred'
     t.references 'mother'
   end
 
-  create_table 'label_hierarchies', id: false, force: :cascade do |t|
+  create_table Label.hierarchy_class.table_name, id: false, force: :cascade do |t|
     t.references 'ancestor', null: false
     t.references 'descendant', null: false
     t.integer 'generations', null: false
   end
 
-  create_table 'cuisine_types', force: :cascade do |t|
+  add_index Label.hierarchy_class.table_name, %i[ancestor_id descendant_id generations], unique: true,
+                                                                                         name: 'lh_anc_desc_idx'
+  add_index Label.hierarchy_class.table_name, [:descendant_id], name: 'lh_desc_idx'
+
+  create_table CuisineType.table_name, force: :cascade do |t|
     t.string 'name'
     t.references 'parent'
   end
 
-  create_table 'cuisine_type_hierarchies', id: false, force: :cascade do |t|
+  create_table CuisineType.hierarchy_class.table_name, id: false, force: :cascade do |t|
     t.references 'ancestor', null: false
     t.references 'descendant', null: false
     t.integer 'generations', null: false
   end
 
-  create_table 'namespace_types', force: :cascade do |t|
+  create_table Namespace::Type.table_name, force: :cascade do |t|
     t.string 'name'
     t.references 'parent'
   end
 
-  create_table 'namespace_type_hierarchies', id: false, force: :cascade do |t|
+  create_table Namespace::Type.hierarchy_class.table_name, id: false, force: :cascade do |t|
     t.references 'ancestor', null: false
     t.references 'descendant', null: false
     t.integer 'generations', null: false
   end
 
-  create_table 'metal', force: :cascade do |t|
+  create_table Metal.table_name, force: :cascade do |t|
     t.references 'parent'
     t.string 'metal_type'
     t.string 'value'
@@ -120,38 +142,38 @@
     t.integer 'sort_order'
   end
 
-  create_table 'metal_hierarchies', id: false, force: :cascade do |t|
+  create_table Metal.hierarchy_class.table_name, id: false, force: :cascade do |t|
     t.references 'ancestor', null: false
     t.references 'descendant', null: false
     t.integer 'generations', null: false
   end
 
-  create_table 'menu_items', force: :cascade do |t|
-    t.string 'name'
-    t.references 'parent'
-    t.timestamps null: false
-  end
+  add_foreign_key(Tag.table_name, Tag.table_name, column: 'parent_id', on_delete: :cascade)
+  add_foreign_key(User.table_name, User.table_name, column: 'referrer_id', on_delete: :cascade)
+  add_foreign_key(Label.table_name, Label.table_name, column: 'mother_id', on_delete: :cascade)
+  add_foreign_key(Metal.table_name, Metal.table_name, column: 'parent_id', on_delete: :cascade)
+  add_foreign_key(Tag.hierarchy_class.table_name, Tag.table_name, column: 'ancestor_id', on_delete: :cascade)
+  add_foreign_key(Tag.hierarchy_class.table_name, Tag.table_name, column: 'descendant_id', on_delete: :cascade)
+end
 
-  create_table 'menu_item_hierarchies', id: false, force: :cascade do |t|
-    t.references 'ancestor', null: false
-    t.references 'descendant', null: false
-    t.integer 'generations', null: false
+SecondDatabaseRecord.establish_connection
+SecondDatabaseRecord.connection_pool.with_connection do |connection|
+  ActiveRecord::Schema.define(version: 0) do
+    connection.create_table MenuItem.table_name, force: :cascade do |t|
+      t.string 'name'
+      t.references 'parent'
+      t.timestamps null: false
+    end
+
+    connection.create_table MenuItem.hierarchy_class.table_name, id: false, force: :cascade do |t|
+      t.references 'ancestor', null: false
+      t.references 'descendant', null: false
+      t.integer 'generations', null: false
+    end
+    connection.add_foreign_key(MenuItem.table_name, MenuItem.table_name, column: 'parent_id', on_delete: :cascade)
+    connection.add_foreign_key(MenuItem.hierarchy_class.table_name, MenuItem.table_name, column: 'ancestor_id',
+                                                                                         on_delete: :cascade)
+    connection.add_foreign_key(MenuItem.hierarchy_class.table_name, MenuItem.table_name, column: 'descendant_id',
+                                                                                         on_delete: :cascade)
   end
-
-  add_index 'label_hierarchies', %i[ancestor_id descendant_id generations], unique: true,
-                                                                            name: 'lh_anc_desc_idx'
-  add_index 'label_hierarchies', [:descendant_id], name: 'lh_desc_idx'
-  add_index 'referral_hierarchies', %i[ancestor_id descendant_id generations], unique: true,
-                                                                               name: 'ref_anc_desc_idx'
-  add_index 'referral_hierarchies', [:descendant_id], name: 'ref_desc_idx'
-
-  add_foreign_key(:tags, :tags, column: 'parent_id', on_delete: :cascade)
-  add_foreign_key(:users, :users, column: 'referrer_id', on_delete: :cascade)
-  add_foreign_key(:labels, :labels, column: 'mother_id', on_delete: :cascade)
-  add_foreign_key(:metal, :metal, column: 'parent_id', on_delete: :cascade)
-  add_foreign_key(:menu_items, :menu_items, column: 'parent_id', on_delete: :cascade)
-  add_foreign_key(:menu_item_hierarchies, :menu_items, column: 'ancestor_id', on_delete: :cascade)
-  add_foreign_key(:menu_item_hierarchies, :menu_items, column: 'descendant_id', on_delete: :cascade)
-  add_foreign_key(:tag_hierarchies, :tags, column: 'ancestor_id', on_delete: :cascade)
-  add_foreign_key(:tag_hierarchies, :tags, column: 'descendant_id', on_delete: :cascade)
 end
diff --git a/test/closure_tree/model_test.rb b/test/closure_tree/model_test.rb
index f05783a..a17dc0a 100644
--- a/test/closure_tree/model_test.rb
+++ b/test/closure_tree/model_test.rb
@@ -7,3 +7,17 @@
     assert_equal Tag._ct, Tag.new._ct
   end
 end
+
+describe 'multi database support' do
+  it 'should have a different connection for menu items' do
+    # These 2 models are in the same database
+    assert_equal Tag.connection, Metal.connection
+    # The hierarchy table is in the same database
+    assert_equal Tag.connection, TagHierarchy.connection
+
+    # However, these 2 models are in different databases
+    refute_equal MenuItem.connection, Tag.connection
+    # The hierarchy table is in the same database
+    assert_equal MenuItem.connection, MenuItemHierarchy.connection
+  end
+end
diff --git a/test/closure_tree/pool_test.rb b/test/closure_tree/pool_test.rb
index db5dfc6..0250cf7 100644
--- a/test/closure_tree/pool_test.rb
+++ b/test/closure_tree/pool_test.rb
@@ -9,8 +9,7 @@ class TypeDuplicate < ActiveRecord::Base
       has_closure_tree
     end
 
-    refute ActiveRecord::Base.connection_pool.active_connection?
-    # +false+ in AR 4, +nil+ in AR 5
+    assert_nil TypeDuplicate.connection_pool.active_connection?
   end
 
   it 'returns connection to the pool after has_closure_tree setup with order' do
@@ -19,7 +18,7 @@ class MetalDuplicate < ActiveRecord::Base
       has_closure_tree order: 'sort_order', name_column: 'value'
     end
 
-    refute ActiveRecord::Base.connection_pool.active_connection?
+    refute MetalDuplicate.connection_pool.active_connection?
   end
 
   it 'returns connection to the pool after has_closure_tree_root setup' do
@@ -28,6 +27,6 @@ class GroupDuplicate < ActiveRecord::Base
       has_closure_tree_root :root_user
     end
 
-    refute ActiveRecord::Base.connection_pool.active_connection?
+    refute GroupDuplicate.connection_pool.active_connection?
   end
 end
diff --git a/test/test_helper.rb b/test/test_helper.rb
index c4ff05b..06053b9 100644
--- a/test/test_helper.rb
+++ b/test/test_helper.rb
@@ -1,49 +1,51 @@
 # frozen_string_literal: true
 
-require 'erb'
 require 'active_record'
-require 'with_advisory_lock'
-require 'tmpdir'
-require 'securerandom'
 require 'minitest'
 require 'minitest/autorun'
 require 'database_cleaner'
 require 'support/query_counter'
 require 'parallel'
 
+puts "Using ActiveRecord #{ActiveRecord.gem_version} and #{RUBY_ENGINE} #{RUBY_ENGINE_VERSION} as #{RUBY_VERSION}"
+
+primary_database_url = ENV['DATABASE_URL'].presence || "sqlite3:///tmp/closure_tree_test"
+secondary_database_url = ENV['SECONDARY_DATABASE_URL'].presence || "sqlite3:///tmp/closure_tree_test-s"
+
+puts "Using primary database #{primary_database_url}"
+puts "Using secondary database #{secondary_database_url}"
+
 ActiveRecord::Base.configurations = {
   default_env: {
-    url: ENV.fetch('DATABASE_URL', "sqlite3://#{Dir.tmpdir}/#{SecureRandom.hex}.sqlite3"),
-    properties: { allowPublicKeyRetrieval: true } # for JRuby madness
+    primary: {
+      url: primary_database_url,
+      properties: { allowPublicKeyRetrieval: true } # for JRuby madness
+    },
+    secondary: {
+      url: secondary_database_url,
+      properties: { allowPublicKeyRetrieval: true } # for JRuby madness
+    }
   }
 }
 
 ENV['WITH_ADVISORY_LOCK_PREFIX'] ||= SecureRandom.hex
 
-ActiveRecord::Base.establish_connection
-
 def env_db
-  @env_db ||= if ActiveRecord::Base.respond_to?(:connection_db_config)
-                ActiveRecord::Base.connection_db_config.adapter
-              else
-                ActiveRecord::Base.connection_config[:adapter]
-              end.to_sym
+  @env_db ||= ActiveRecord::Base.connection_db_config.adapter.to_sym
 end
 
 ActiveRecord::Migration.verbose = false
 ActiveRecord::Base.table_name_prefix = ENV['DB_PREFIX'].to_s
 ActiveRecord::Base.table_name_suffix = ENV['DB_SUFFIX'].to_s
-ActiveRecord::Base.establish_connection
 
 # Use in specs to skip some tests
 def sqlite?
   env_db == :sqlite3
 end
 
-ActiveRecord::Base.connection.recreate_database('closure_tree_test') unless sqlite?
-puts "Testing with #{env_db} database, ActiveRecord #{ActiveRecord.gem_version} and #{RUBY_ENGINE} #{RUBY_ENGINE_VERSION} as #{RUBY_VERSION}"
 
 DatabaseCleaner.strategy = :truncation
+DatabaseCleaner.allow_remote_database_url = true
 
 module Minitest
   class Spec
@@ -65,5 +67,8 @@ class Spec
 Thread.abort_on_exception = true
 
 require 'closure_tree'
+
+
 require_relative '../spec/support/schema'
-require_relative '../spec/support/models'
+
+puts "Testing with #{env_db} database"