class DatabaseCleaner::Strategy

def clean

Override this method with the actual cleaning procedure. Its the only mandatory method implementation. 
def clean
  raise NotImplementedError
end

def cleaning(&block) 

def cleaning(&block)
  begin
    start
    yield
  ensure
    clean
  end
end

def db 

def db
  @db ||= :default
end

def initialize(options=nil)

Override this method if the strategy accepts options 
def initialize(options=nil)
  if options
    name = self.class.name.sub("DatabaseCleaner::","").sub("::"," ") # e.g. "ActiveRecord Transaction"
    raise ArgumentError, "No options are available for the #{name} strategy."
  end
end

def start

Override this method to start a database transaction if the strategy uses them 
def start
end