What is the best approach to save multiple temperature-curves (which are measured at the same time) in a Database using Rails and SQL

Question

what is the best approach to save multiple temperature-curves by using Ruby On Rails and a SQL-database. The temperature curves are are measured at the same time. And the time for each measured value musst be stored in seconds.

This picute show my problem in an UML. But the assoziation between timeline and curve-measurment isn't correct. Each timeline-value can have several curve-measurments but not in the same curve. In the same curve alle timeline-values must be unique.

In this solution all timeline-values can have several curve-measurments. This ist correct but in this picutre a timeline-value can have several curve-mesaurments in the same curve and that is wrong.

I hope you understand my problem and you can give me some hint to a better approach.

Answer 1

It looks like your CurveMeasurement should be a join between Curve and Timeline:

class Curve < ActiveRecord::Base
  has_many :curve_measurements
  ...
end

class Timeline < ActiveRecord::Base
  has_many :curve_measurements
  ...
end

class CurveMeasurement < ActiveRecord::Base
  belongs_to :curve
  belongs_to :timeline

  validates :curve_id, uniqueness: { scope: :timeline_id }
  validates :timeline_id, uniqueness: { scope: :curve_id }
  ...
end

The important parts for your requirements are the uniqueness scopes in the CurveMeasurement model - this ensures that you can't have more than one measurement for a given curve at a given timeline point.

---

It would also be possible to do this without the timeline value being a separate model:

class Curve < ActiveRecord::Base
  has_many :curve_measurements
  ...
end

class CurveMeasurement < ActiveRecord::Base
  belongs_to :curve

  validates :timeline_value, uniqueness: { scope: :curve_id }
  ...
end

If you wanted to enforce a discrete set of timeline_values, you can use further validations: either numericality or inclusion (see http://guides.rubyonrails.org/active_record_validations.html )