true sting to true in rails
f you use Rails 5, you can do ActiveModel::Type::Boolean.new.cast(value).
In Rails 4.2, use ActiveRecord::Type::Boolean.new.type_cast_from_user(value).
Rails 5 Source: https://github.com/rails/rails/blob/5-1-stable/activemodel/lib/active_model/type/boolean.rb
ActiveModel::Type::Boolean.new.cast('t') # => true
ActiveModel::Type::Boolean.new.cast('true') # => true
ActiveModel::Type::Boolean.new.cast(true) # => true
ActiveModel::Type::Boolean.new.cast('1') # => true
ActiveModel::Type::Boolean.new.cast('f') # => false
ActiveModel::Type::Boolean.new.cast('0') # => false
ActiveModel::Type::Boolean.new.cast('false') # => false
ActiveModel::Type::Boolean.new.cast(false) # => false
ActiveModel::Type::Boolean.new.cast(nil) # => nil