Comparing database fields/columns with each other inside validations in Ruby on Rails

Question

I have the following model in Rails which manages a Diabetes Settings table:

class DiabetesSetting < ApplicationRecord
    belongs_to :user

    validates :bs_min, :bs_max, :bs_target, :correction_number, numericality: { only_integer: true }
    validates :correction_insulin, numericality: true
    validates :bs_min {less_than: :bs_max }
    validates :bs_max {greater_than: :bs_min}
    validates :bs_target {less_than: :bs_max}

end

My Question: Is something like this, to compare the fields of a database with each other to validate, that when a new setting is created, one value is higher or lower than the other, possible in Rails or do I have to write custom validation methods for this?

To clarify: bs_min is the mimmum value of a numerical range and bs_max the max value of a numerical range. They are both attributes inside the diabetes settings model. The Question is if I can compare these values like I did or if I have to write custom methods to validate

Thanks in advance for Your help

Can you describe more details about what actually you want to validate? — Tai
– Tai, Commented Jan 24, 2018 at 14:54
@Tai sure. I updated the Question. The main question is , though is it possible to validate the way I did or do I have to write custom validation methods? Thank You :-) — Sebastian Peter
– Sebastian Peter, Commented Jan 24, 2018 at 15:01
@Anthony Shit, I thought so ;-) Would have been to good to be true if it would work the way I wrote it above — Sebastian Peter
– Sebastian Peter, Commented Jan 24, 2018 at 15:07

Tai · Accepted Answer · 2018-01-24 15:45:06Z

1

You can do it using Rail's built-in validations. Try below code:

class DiabetesSetting < ApplicationRecord
  ...
  validates_numericality_of :bs_min,    { less_than: :bs_max }
  validates_numericality_of :bs_max,    { greater_than: :bs_min }
  validates_numericality_of :bs_target, { less_than: :bs_max }
end

Refer to following link for numerical validation: http://api.rubyonrails.org/classes/ActiveModel/Validations/HelperMethods.html#method-i-validates_numericality_of

answered Jan 24, 2018 at 15:45

Tai

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4 Comments

Tai Over a year ago

Have you tried it? Which Rails version are you using?

Tai Over a year ago

Yes, I tried. Rails 5.0.0. Validate it in Rails console.

Sebastian Peter Over a year ago

Hey thanks for the effort but this is not working. When testing the model with unit tests and and setting up a valid instance of the model, the test fails.

Sebastian Peter Over a year ago

@Anthony was right. When comparing data fielsd with each other inside validations you need to write custom validators.

spickermann · Accepted Answer · 2022-01-04 19:06:58Z

1

Ruby on Rails 7.0 added support for validates_comparison_of validations like this

validates :bs_min, comparison: { less_than: :bs_max }
validates :bs_max, comparison: { greater_than: :bs_min }
validates :bs_target, comparison: { less_than: :bs_max }

answered Jan 4, 2022 at 19:06

spickermann

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