Add support for default strategy for each ORM

DatabaseCleaner will select the best default strategy based on the ORM you're using without having you to select it by yourself.

* ActiveRecord, DataMapper => :transaction
* MongoMapper, Mongoid, CouchPotato => :truncation

README.textile

@@ -10,19 +10,20 @@ ActiveRecord, DataMapper, MongoMapper, Mongoid, and CouchPotato are supported.
 Here is an overview of the strategies supported for each library:
 
 |_. ORM        |_.  Truncation  |_.  Transaction  |_.  Deletion    |
-| ActiveRecord | Yes            | Yes             | Yes            |
-| DataMapper   | Yes            | Yes             | No             |
-| CouchPotato  | Yes            | No              | No             |
-| MongoMapper  | Yes            | No              | No             |
-| Mongoid      | Yes            | No              | No             |
+| ActiveRecord | Yes            | **Yes**         | Yes            |
+| DataMapper   | Yes            | **Yes**         | No             |
+| CouchPotato  | **Yes**        | No              | No             |
+| MongoMapper  | **Yes**        | No              | No             |
+| Mongoid      | **Yes**        | No              | No             |
+
+(Default strategy for each library is denoted in bold)
 
 The ActiveRecord @:deletion@ strategy is only useful for when the @:truncation@ strategy causes
 locks (as reported by some Oracle DB users).  The @:truncation@ strategy is the preferred option
 since it is much faster.
 
 Database Cleaner also includes a @null@ strategy (that does no cleaning at all) which can be used 
-with any ORM library.  _This is the default strategy and will be used unless you
-specify one._ You can also explicitly use it by setting your strategy to @nil@.
+with any ORM library. You can also explicitly use it by setting your strategy to @nil@.
 
 h2. How to use
 

examples/features/support/env.rb

@@ -54,9 +54,9 @@ if orm && strategy
     DatabaseCleaner[         orm.gsub(/(.)([A-Z]+)/,'\1_\2').downcase.to_sym ].strategy = strategy.to_sym
     DatabaseCleaner[ another_orm.gsub(/(.)([A-Z]+)/,'\1_\2').downcase.to_sym ].strategy = strategy.to_sym
   else
-    DatabaseCleaner.strategy = strategy.to_sym
+    DatabaseCleaner.strategy = strategy.to_sym unless strategy == "default"
   end
 
 else
-  raise "Run 'ORM=ActiveRecord|DataMapper|MongoMapper|CouchPotato [ANOTHER_ORM=...] [MULTIPLE_DBS=true] STRATEGY=transaction|truncation cucumber examples/features'"
+  raise "Run 'ORM=ActiveRecord|DataMapper|MongoMapper|CouchPotato [ANOTHER_ORM=...] [MULTIPLE_DBS=true] STRATEGY=transaction|truncation|default cucumber examples/features'"
 end

features/cleaning_default_strategy.feature

@@ -0,0 +1,19 @@
+Feature: database cleaning
+  In order to ease example and feature writing
+  As a developer
+  I want to have my database in a clean state with default strategy
+
+  Scenario Outline: ruby app
+    Given I am using <ORM>
+    And the default cleaning strategy
+
+    When I run my scenarios that rely on a clean database
+    Then I should see all green
+
+  Examples:
+    | ORM          |
+    | ActiveRecord |
+    | DataMapper   |
+    | MongoMapper  |
+    | Mongoid      |
+    | CouchPotato  |

lib/database_cleaner/base.rb

@@ -9,6 +9,7 @@ module DatabaseCleaner
         self.orm = desired_orm
       end
       self.db = opts[:connection] if opts.has_key? :connection
+      set_default_orm_strategy
     end
 
     def db=(desired_db)
@@ -122,5 +123,14 @@ module DatabaseCleaner
         end
       end
     end
+
+    def set_default_orm_strategy
+      case orm
+      when :active_record, :data_mapper
+        self.strategy = :transaction
+      when :mongo_mapper, :mongoid, :couch_potato
+        self.strategy = :truncation
+      end
+    end
   end
 end

spec/database_cleaner/base_spec.rb

@@ -1,6 +1,9 @@
 require File.dirname(__FILE__) + '/../spec_helper'
 require 'database_cleaner/active_record/transaction'
 require 'database_cleaner/data_mapper/transaction'
+require 'database_cleaner/mongo_mapper/truncation'
+require 'database_cleaner/mongoid/truncation'
+require 'database_cleaner/couch_potato/truncation'
 
 module DatabaseCleaner
   describe Base do
@@ -310,7 +313,9 @@ module DatabaseCleaner
     end
 
     describe "strategy" do
-      it "returns a null strategy when strategy no set" do
+      subject { ::DatabaseCleaner::Base.new :a_orm }
+
+      it "returns a null strategy when strategy no set and undetectable" do
         subject.instance_values["@strategy"] = nil
         subject.strategy.should == DatabaseCleaner::NullStrategy
       end
@@ -442,5 +447,32 @@ module DatabaseCleaner
 
     end
 
+    describe 'set_default_orm_strategy' do
+      it 'sets strategy to :transaction for ActiveRecord' do
+        cleaner = DatabaseCleaner::Base.new(:active_record)
+        cleaner.strategy.should be_instance_of DatabaseCleaner::ActiveRecord::Transaction
+      end
+
+      it 'sets strategy to :transaction for DataMapper' do
+        cleaner = DatabaseCleaner::Base.new(:data_mapper)
+        cleaner.strategy.should be_instance_of DatabaseCleaner::DataMapper::Transaction
+      end
+
+      it 'sets strategy to :truncation for MongoMapper' do
+        cleaner = DatabaseCleaner::Base.new(:mongo_mapper)
+        cleaner.strategy.should be_instance_of DatabaseCleaner::MongoMapper::Truncation
+      end
+
+      it 'sets strategy to :truncation for Mongoid' do
+        cleaner = DatabaseCleaner::Base.new(:mongoid)
+        cleaner.strategy.should be_instance_of DatabaseCleaner::Mongoid::Truncation
+      end
+
+      it 'sets strategy to :truncation for CouchPotato' do
+        cleaner = DatabaseCleaner::Base.new(:couch_potato)
+        cleaner.strategy.should be_instance_of DatabaseCleaner::CouchPotato::Truncation
+      end
+    end
+
   end
 end