All changes required for rails 3.2 are also required for rails 3.1.

Replace all rails32? with rails31?

lib/db_charmer.rb

@@ -14,9 +14,9 @@ def self.rails3?
     ::ActiveRecord::VERSION::MAJOR > 2
   end
 
-  # Used in all Rails3.2-specific places
-  def self.rails32?
-    rails3? && ::ActiveRecord::VERSION::MINOR >= 2
+  # Used in all Rails3.1-specific places
+  def self.rails31?
+    rails3? && ::ActiveRecord::VERSION::MINOR >= 1
   end
 
   # Used in all Rails2-specific places
@@ -139,13 +139,13 @@ def self.with_all_hijacked
 
 # Enable connection proxy for associations
 # WARNING: Inject methods to association class right here (they proxy include calls somewhere else, so include does not work)
-association_proxy_class = DbCharmer.rails32? ? ActiveRecord::Associations::CollectionProxy : ActiveRecord::Associations::AssociationProxy
+association_proxy_class = DbCharmer.rails31? ? ActiveRecord::Associations::CollectionProxy : ActiveRecord::Associations::AssociationProxy
 association_proxy_class.class_eval do
   def proxy?
     true
   end
 
-  if DbCharmer.rails32?
+  if DbCharmer.rails31?
     def on_db(con, proxy_target = nil, &block)
       proxy_target ||= self
       @association.klass.on_db(con, proxy_target, &block)
@@ -178,8 +178,8 @@ def on_master(&block)
 require 'db_charmer/active_record/migration/multi_db_migrations'
 ActiveRecord::Migration.send(:include, DbCharmer::ActiveRecord::Migration::MultiDbMigrations)
 
-if DbCharmer.rails32?
-  require 'db_charmer/rails32/active_record/migration/command_recorder'
+if DbCharmer.rails31?
+  require 'db_charmer/rails31/active_record/migration/command_recorder'
   ActiveRecord::Migration::CommandRecorder.send(:include, DbCharmer::ActiveRecord::Migration::CommandRecorder)
 end
 
@@ -195,10 +195,10 @@ def on_master(&block)
 ActiveRecord::Base.extend(DbCharmer::ActiveRecord::DbMagic)
 
 # Setup association preload magic
-if DbCharmer.rails32?
-  require 'db_charmer/rails32/active_record/preloader/association'
+if DbCharmer.rails31?
+  require 'db_charmer/rails31/active_record/preloader/association'
   ActiveRecord::Associations::Preloader::Association.send(:include, DbCharmer::ActiveRecord::Preloader::Association)
-  require 'db_charmer/rails32/active_record/preloader/has_and_belongs_to_many'
+  require 'db_charmer/rails31/active_record/preloader/has_and_belongs_to_many'
   ActiveRecord::Associations::Preloader::HasAndBelongsToMany.send(:include, DbCharmer::ActiveRecord::Preloader::HasAndBelongsToMany)
 else
   require 'db_charmer/active_record/association_preload'

lib/db_charmer/active_record/connection_switching.rb

@@ -38,7 +38,7 @@ def connection_with_magic
           def connection_pool_with_magic
             abstract_connection_class = connection.abstract_connection_class rescue nil # respond_to? doesn't work on connection_proxy...
             if abstract_connection_class
-              connection_handler.retrieve_connection_pool(connection.abstract_connection_class) || connection_pool_without_magic
+              connection_handler.retrieve_connection_pool(abstract_connection_class) || connection_pool_without_magic
             else
               connection_pool_without_magic
             end

lib/db_charmer/active_record/migration/multi_db_migrations.rb

@@ -5,7 +5,7 @@ module MultiDbMigrations
         extend ActiveSupport::Concern
 
         included do
-          if DbCharmer.rails32?
+          if DbCharmer.rails31?
             alias_method_chain :migrate, :db_wrapper
           else
             class << self
@@ -24,7 +24,7 @@ def multi_db_names=(names)
             @@multi_db_names[self.name] = names
           end
 
-          unless DbCharmer.rails32?
+          unless DbCharmer.rails31?
             def migrate_with_db_wrapper(direction)
               if names = multi_db_names
                 names.each do |multi_db_name|