How can I implement custom validations in Ruby on Rails?

How can I implement custom validations in Ruby on Rails?

You can create custom validations in Rails by defining a method in your model and using the validate method.

Can you give me an example of a custom validation?

Sure! For instance, you can validate that a user's age is greater than 18 like this:

class User < ApplicationRecord
  validate :age_must_be_over_18

  def age_must_be_over_18
    if age < 18
      errors.add(:age, 'must be greater than 18')
    end
  end
end

What if I want to validate multiple fields?

You can create a custom validation method that checks multiple fields. Just call errors.add for each field that fails validation.

Is there a way to use built-in validators with custom ones?

Yes, you can combine built-in validators with your custom ones. Just use them in the same model.