Question

I have a Game model which has_many Rounds which has_many Shots.
Per game, each cup hit with a shot should be unique. This is easy enough to do with validates_uniqueness_of :cup using a scope of :game_id.

However, how do I validate that each Shot is an increment of +1 of the last shot? I cannot have users select their first shot as having made cup 4. This would make no sense.

My form is using form_for @round which accepts nested attributes for exactly 6 shots.

How do I implement this validation? Do I need to refactor my view or completely rethink this?

Answer 1

Since you are using Rails 3, you get some nice options here. I’m not sure that I understand your problem completely, but I’m assuming that you want some type of validation where the score starts at 1 and increments each time.

Here’s a test.

  require 'test_helper'

    class ShotTest < ActiveSupport::TestCase
      test "score validations by game" do
        Shot.delete_all # Just to be sure. In a real test setup I would have handled this elsewhere.

        shot = Shot.new(:game_id => 1, :score => 1)
        assert shot.valid?
        shot.save!

        assert ! Shot.new(:game_id => 1, :score => 1).valid?
        assert ! Shot.new(:game_id => 1, :score => 3).valid?
        assert   Shot.new(:game_id => 1, :score => 2).valid?

        assert   Shot.new(:game_id => 2, :score => 1).valid?
      end
    end

And an example model.

# Stick this in a lib file somewhere
class IncrementValidator < ActiveModel::EachValidator
  def validate_each(record, attribute, value)
    record.errors[attribute] << "must increment score by +1 " unless value == (Shot.maximum(:score, :conditions => {:game_id => record.game_id} ).to_i + 1)
  end
end

class Shot < ActiveRecord::Base
  validates :score, :uniqueness => {:scope => :game_id}, :increment => true
end

Test output:

$ ruby -I./test test/unit/shot_test.rb 
Loaded suite test/unit/shot_test
Started
.
Finished in 0.042116 seconds.

1 tests, 5 assertions, 0 failures, 0 errors