Reset ids option (#71)

Implement resetting ids for deletion strategy.

README.md

@@ -61,6 +61,8 @@ DatabaseCleaner[:active_record].strategy = DatabaseCleaner::ActiveRecord::Deleti
 
 * `: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 (1) you create and drop tables in your tests, or (2) you change Postgres schemas (`ActiveRecord::Base.connection.schema_search_path`) in your tests (for example, in a multitenancy setup with each tenant in a different Postgres schema). Defaults to `true`.
 
+* `:reset_ids` - Only valid for deletion strategy, when set to `true` resets ids to 1 after each table is cleaned.
+
 ## Adapter configuration options
 
 `#db` defaults to the default ActiveRecord database, but can be specified manually in a few ways:

lib/database_cleaner/active_record/deletion.rb

@@ -19,13 +19,27 @@ def clean
       def delete_tables(connection, table_names)
         table_names.each do |table_name|
           delete_table(connection, table_name)
+          reset_id_sequence(connection, table_name) if @reset_ids
         end
       end
 
       def delete_table connection, table_name
         connection.execute("DELETE FROM #{connection.quote_table_name(table_name)} WHERE 1=1")
       end
 
+      def reset_id_sequence connection, table_name
+        case connection.adapter_name
+        when 'Mysql2'
+          connection.execute("ALTER TABLE #{table_name} AUTO_INCREMENT = 1;")
+        when 'SQLite'
+          connection.execute("delete from sqlite_sequence where name='#{table_name}';")
+        when 'PostgreSQL'
+          connection.reset_pk_sequence!(table_name)
+        else
+          raise "reset_id option not supported for #{connection.adapter_name}"
+        end
+      end
+
       def tables_to_truncate(connection)
         if information_schema_exists?(connection)
           @except += connection.database_cleaner_view_cache + migration_storage_names

lib/database_cleaner/active_record/truncation.rb

@@ -5,13 +5,14 @@ module DatabaseCleaner
   module ActiveRecord
     class Truncation < Base
       def initialize(opts={})
-        if !opts.empty? && !(opts.keys - [:only, :except, :pre_count, :cache_tables]).empty?
-          raise ArgumentError, "The only valid options are :only, :except, :pre_count, and :cache_tables. You specified #{opts.keys.join(',')}."
+        if !opts.empty? && !(opts.keys - [:only, :except, :pre_count, :cache_tables, :reset_ids]).empty?
+          raise ArgumentError, "The only valid options are :only, :except, :pre_count, :reset_ids, and :cache_tables. You specified #{opts.keys.join(',')}."
         end
 
         @only = Array(opts[:only]).dup
         @except = Array(opts[:except]).dup
 
+        @reset_ids = opts[:reset_ids]
         @pre_count = opts[:pre_count]
         @cache_tables = opts.has_key?(:cache_tables) ? !!opts[:cache_tables] : true
       end

spec/database_cleaner/active_record/deletion_spec.rb

@@ -42,6 +42,14 @@
             expect(User.create.id).to eq 3
           end
 
+          context "reset_ids option set to true" do
+            subject(:strategy) { described_class.new(reset_ids: true) }
+            it "should reset AUTO_INCREMENT index of table" do
+              strategy.clean
+              expect(User.create.id).to eq 1
+            end
+          end
+
           it "should delete from all tables except for schema_migrations" do
             expect { strategy.clean }
               .to_not change { connection.select_value("select count(*) from schema_migrations;").to_i }