How to remove validation using instance_eval clause in Rails?

Question

I would like to enhance existing class using instance_eval. There original definition contains validation, which require presence of certain fields, ie:

class Du         


        

Answer 1

For rails 4.2 (~ 5.0) it can be used the following module with a method:

module ValidationCancel
   def cancel_validates *attributes
      attributes.select {|v| Symbol === v }.each do |attr|
         self._validators.delete( attr )

         self._validate_callbacks.select do |callback|
            callback.raw_filter.try( :attributes ) == [ attr ] ;end
         .each do |vc|
            self._validate_callbacks.delete( vc ) ;end ;end ;end ;end

Note: Since the filtern can be a symbol of an association, or a specific validator, so we have to use #try.

Then we can use rails-friendly form in a class declaration:

class Dummy
   extend ValidationCancel
   cancel_validates :field ;end

Note: since removal of the validator is affecting to the whole class and its descendants globally, it is not recommended to use it to remove validations in such way, instead add if clause for the specific rule as follows:

module ValidationCancel
   def cancel_validates *attributes
      this = self
      attributes.select {|v| Symbol === v }.each do |attr|
         self._validate_callbacks.select do |callback|
            callback.raw_filter.try( :attributes ) == [ attr ] ;end
         .each do |vc|
            ifs = vc.instance_variable_get( :@if )
            ifs << proc { ! self.is_a?( this ) } ;end ;end ;end ;end

This restricts execution of the validation callback for the specified class and its descendants.