undefined method `find_by_contents’ ,acts_as_ferret

Problem
When trying to use the acts_as_ferret plugin in a search page by using the find_by_contents method then the following error appears:

undefined method `find_by_contents'

Solution
It seems that the API of the plugin has changed, and the

find_by_contents

method should be replaced with the:

find_with_ferret

method