Question

I have three models named Metric, Entry, and Measurement:

class Metric < ActiveRecord::Base
  has_many :entries
  attr_accessible :name, :required_measurements, :optional_measurements
end

class Entry < ActiveRecord::Base
  belongs_to :metric
  has_many :measurements
  attr_accessible :metric_id
end

class Measurement < ActiveRecord::Base
  belongs_to :entry
  attr_accessible :name, :value
end

They are associated, and I can create nested instances of each this way:

bp = Metric.create(:name => "Blood Pressure", :required_measurement_names => ["Diastolic", "Systolic"])

bp_entry = bp.entries.create()

bp_entry.measurements.create({:name => "Systolic", :value =>140}, {:name => "Diastolic", :value =>90})

How do I validate the measurements for blood pressure based on the :required_measurement_names attribute in the Metric model? For example, how would I ensure that only “Systolic” and “Diastolic” are entered as measurements?

Is there a better way to about setting up these associations and validations?

Thanks!

Answer 1

Looks like entry is a join model between Measurement and Metric. so it makes sense for your validation to go there.

To ensure that all metrics required metrics are covered

def validate_required_measurements
  metric.required_measurements.each{ |requirement| 
     unless (measurements.map{|measurement| measurement.name}.includes requirement)
       errors.add_to_base "required measurement #{requirement} is missing"  
     end
  }
end

To ensure that only accepted metrics are included (assuming optional metrics are accepted too).

def validate_accepted_measurements
  measurements.each{ |measurement| 
     unless ((metric.required_measurements + metric.optional_measurements).include measurement.name )
       errors.add_to_base "invalid measurement #{measurement.name} for metric"  
     end
  }
end

Putting it all together add the above and following to the Entry model

validate: validate_accepted_measurements, :validate_required_measurements

N.B. my Ruby is a little rusty so this isn’t guaranteed to work after copying and pasting, but it should get you close enough to fix the syntax errors that slipped through.