By: Bruce Bahlmann - Contributing Author (your feedback is important to us!)

In rails development, when creating web forms, you often have a particular field dependent on another. For example, lets say you have a checkbox (boolean) input value whose value controls the need for an additional text input value. As such, when adding validation to to these fields within the model, you must either make these fields optional, or if you want to make them dependent on the setting of this checkbox (used in this particular example) you need to use a conditional.

Fortunately, Ruby on Rails (RoR) provides an easy way to validate these without creating a "custom validation" (which is an alternative way to do this, albeit more complicated). Simply place the [:if] after the validates entry for the field which is dependent on another input field.

Class Post < ActiveRecord::Base
  Validates :<field name>, :presence => true, :if => "<field checked> == true"
end

The above entry with in app/models/post.rb reads as follows. Validates would require the presence of a value within the <field name> (name of the text input field) IF the <field check> (the name of the checkbox input field) was set to true.

Note: a checkbox field is not "nil", rather it is either true if checked, or false if either not checked or not set.

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