Plain Old Ruby Objects + Rails Validations = self-checking Ruby objects.
- Very readable error messages
- Clean, minimal syntax
This is a small layer around ActiveModel::Validations. (About 18 lines of code.) So if you know how to use Rails Validations, you're good to go. I wrote this to help with CSV data imports and website microdata generation.
Writing a self-validating object
All of the ActiveModel::Validations are available, plus a new one,
class Dog < ValidatedObject::Base # Plain old Ruby attr_accessor :name, :birthday # attr_reader is supported as well for read-only attributes # Plain old Rails validates :name, presence: true # A new type-validation if you'd like to use it validates :birthday, type: Date, allow_nil: true # Strongly typed but optional end
TypeValidator is what enables
type: Date, above. All classes can be checked, as well as a pseudo-class
#... validates :premium_membership, type: Boolean #...
Instantiating and automatically validating
# This Dog instance validates itself at the end of instantiation. spot = Dog.new(name: 'Spot')
# We can also explicitly test for validity because all of # ActiveModel::Validations is available. spot.valid? # => true spot.birthday = Date.new(2015, 1, 23) spot.valid? # => true
Good error messages
Any of the standard Validations methods can be
used to test an instance, plus the custom
check_validations! convenience method:
spot.birthday = '2015-01-23' spot.valid? # => false spot.check_validations! # => ArgumentError: Birthday is a String, not a Date
Note the clear, explicit error message. These are great when reading a log file following a data import. It describes all the invalid conditions. Let's test it by making another attribute invalid:
spot.name = nil spot.check_validations! # => ArgumentError: Name can't be blank; Birthday is a String, not a Date
Use in parsing data
I often use a validated object in a loop to import data, e.g.:
# Import a CSV file of dogs dogs =  csv.next_row do |row| begin dogs << Dog.new(name: row.name) rescue ArgumentError => e logger.warn(e) end end
The result is that
dogs is an array of guaranteed valid Dog objects. And the
error log lists unparseable rows with good info for tracking down problems in
Use in code generation
My Schema.org microdata generation gem uses ValidatedObjects to recursively create well formed HTML / JSON-LD.
Add this line to your application's Gemfile:
And then execute:
Or install it yourself as:
$ gem install validated_object
(TODO: Verify these instructions.) After checking out the repo, run
to install dependencies. Then, run
rake spec to run the tests. You can also
bin/console for an interactive prompt that will allow you to experiment.
To install this gem onto your local machine, run
bundle exec rake install. To
release a new version, update the version number in
version.rb, and then run
bundle exec rake release, which will create a git tag for the version, push
git commits and tags, and push the
.gem file to
Bug reports and pull requests are welcome on GitHub at https://github.com/dogweather/validated_object.
The gem is available as open source under the terms of the MIT License.