Select, Checkbox, and Radio button elements in Sinatra with Datamapper - ruby

Question

Using Datamapper with Sinatra, it's really easy to save text properties:
DataMapper::setup(:default, "sqlite3://#{Dir.pwd}/tailor.db")
class Person
include DataMapper::Resource
property :id, Serial
property :name, String, :required => true
property :height, String, :required => false
end
DataMapper.finalize.auto_upgrade!
...
put '/:id/edit' do
p = Person.get params[:id]
p.name = params[:name]
p.height = params[:height]
p.save
end
And the view:
%form
%input{:type => 'text', :name => 'name'}
%input{:type => 'text', :name => 'height'}
%input{:type => 'submit', :value => 'Save'}
With :type => 'text' it is a breeze. However, I'm running into trouble trying to set a boolean (property :test, Boolean, :required => false) with a checkbox. This question is similar, but doesn't address how to do a simple boolean.
In addition, what is the easiest way to set up values that don't accept any string, but rather just a set of predefined options—either as a select that allows one choice, or a set of radio buttons that allows several?
EDIT:
I figured out checkboxes:
p.bool = !params[:bool].nil?
and in the view:
%input{:type => 'checkbox', :name => 'bool', :value => "#{#bool}", :checked => #p.bool}

Answer 1

When you submit a form with a checkbox, if you don’t specify the value form it the default is the string on. Additionally, if the checkbox isn’t selected it doesn’t get submitted at all. So the result is that in your handler, params[:test] (assuming the checkbox is named test) is either nil if it was unchecked, or the string on if it was.
A boolean property in Datamapper is expecting to be assigned either a Boolean (true or false), or one of a small set of values that it will implicitly convert. on and nil are not among those values, so when you try to assign the value to Datamapper it will fail validation and not save:
...
p.test = 'on'
if !p.save
p p.errors[:test]
end
produces:
["Test must be of type TrueClass"]
One way to fix this is to check in your handler and explicitly convert the value to a boolean when assigning to the property:
p.test = params[:test] == 'on' ? true : false
Another technique is to set the value in the HTML checkbox to one of the values that Datamapper will convert, so you can pass it directly. You can have multiple controls with the same name in a form, and they will be submitted in the order they appear in the page. Sinatra will only use the last one when creating the params hash, so if you add a hidden input with the same name as the checkbox before the checkbox, then if it is not checked the value will be that of the hidden input. If it is checked, its value will override that of the hidden input.
%input{:type => 'hidden', :name => 'foo', :value => 'f'}
%input{:type => 'checkbox', :name => 'foo', :value => 't'}
Now params[:test] will be either 'f' or 't',, both of which Datamapper will convert for you, so you can simply do
p.test = params[:test]