make caching of tables to be truncated optional

README.markdown

@@ -181,6 +181,10 @@ The following options are available for ActiveRecord's `:truncation` strategy _o
 * `:pre_count` - When set to `true` this will check each table for existing rows before truncating it.  This can speed up test suites when many of the tables to be truncated are never populated. Defaults to `:false`. (Also, see the section on [What strategy is fastest?](#what-strategy-is-fastest))
 * `:reset_ids` - This only matters when `:pre_count` is used, and it will make sure that a tables auto-incrementing id is reset even if there are no rows in the table (e.g. records were created in the test but also removed before DatabaseCleaner gets to it). Defaults to `true`.
 
+The following option is available for ActiveRecord's `:truncation` and `:deletion` strategy for any DB.
+
+* `:cache_tables` - When set to `true` the list of tables to truncate or delete from will only be read from the DB once, otherwise it will be read before each cleanup run. Set this to `false` if you create and drop tables in your tests. Defaults to `true`.
+
 
 ### RSpec Example
 

lib/database_cleaner/active_record/truncation.rb

@@ -239,7 +239,8 @@ module DatabaseCleaner::ActiveRecord
     private
 
     def tables_to_truncate(connection)
-      (@only || connection.database_cleaner_table_cache) - @tables_to_exclude - connection.database_cleaner_view_cache
+      tables_in_db = cache_tables? ? connection.database_cleaner_table_cache : connection.tables
+      (@only || tables_in_db) - @tables_to_exclude - connection.database_cleaner_view_cache
     end
 
     # overwritten
@@ -247,6 +248,10 @@ module DatabaseCleaner::ActiveRecord
       [::ActiveRecord::Migrator.schema_migrations_table_name]
     end
 
+    def cache_tables?
+      !!@cache_tables
+    end
+
     def pre_count?
       @pre_count == true
     end

lib/database_cleaner/generic/truncation.rb

@@ -2,8 +2,8 @@ module DatabaseCleaner
   module Generic
     module Truncation
       def initialize(opts={})
-        if !opts.empty? && !(opts.keys - [:only, :except, :pre_count, :reset_ids]).empty?
-          raise ArgumentError, "The only valid options are :only, :except, :pre_count or :reset_ids. You specified #{opts.keys.join(',')}."
+        if !opts.empty? && !(opts.keys - [:only, :except, :pre_count, :reset_ids, :cache_tables]).empty?
+          raise ArgumentError, "The only valid options are :only, :except, :pre_count, :reset_ids or :cache_tables. You specified #{opts.keys.join(',')}."
         end
         if opts.has_key?(:only) && opts.has_key?(:except)
           raise ArgumentError, "You may only specify either :only or :except.  Doing both doesn't really make sense does it?"
@@ -14,6 +14,7 @@ module DatabaseCleaner
         @tables_to_exclude += migration_storage_names
         @pre_count = opts[:pre_count]
         @reset_ids = opts[:reset_ids]
+        @cache_tables = opts.has_key?(:cache_tables) ? !!opts[:cache_tables] : true
       end
 
       def start

spec/database_cleaner/active_record/truncation_spec.rb

@@ -111,6 +111,24 @@ module DatabaseCleaner
             subject.clean
           end
         end
+
+        context 'when :cache_tables is set to true' do
+          it 'caches the list of tables to be truncated' do
+            connection.should_receive(:database_cleaner_table_cache)
+
+            connection.stub!(:truncate_tables)
+            Truncation.new({ :cache_tables => true }).clean
+          end
+        end
+
+        context 'when :cache_tables is set to false' do
+          it 'does not cache the list of tables to be truncated' do
+            connection.should_not_receive(:database_cleaner_table_cache)
+
+            connection.stub!(:truncate_tables)
+            Truncation.new({ :cache_tables => false }).clean
+          end
+        end
       end
 
       describe '#pre_count?' do