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

Answer by aVenger has problems when you declare validations of more than one attribute in a line:

validates :name, :message, :presence => true

That's because this line creates a raw_filter with more than one attribute in attributes filter:

Model.send(:_validate_callbacks)
=> [#<ActiveSupport::Callbacks::Callback:0xa350da4 @klass=Model(...), ... , @raw_filter=#<ActiveModel::Validations::PresenceValidator:0x9da7470 @attributes=[:name, :message], @options={}>, @filter="_callback_before_75", @compiled_options="true", @callback_id=76>]

We have to delete the desired attribute from that array and reject the callbacks without attributes

Dummy.class_eval do

  _validators.reject!{ |key, _| key == :field }

  _validate_callbacks.each do |callback|
    callback.raw_filter.attributes.delete :field
  end

  _validate_callbacks.reject! do |callback|
    callback.raw_filter.attributes.empty? || 
      callback.raw_filter.attributes == [:field]
  end
end

I have this working on a Rails 3.2.11 app.

Answer 2

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.

Answer 3

Assuming the original implementation of Dummy is defined in an engine there is a nasty hack that will do what you want. Define Dummy in your application to keep the original implementation of Dummy from being auto-loaded. Then load the source to Dummy and remove the line that does the validation. Eval the modified source.

Put the following in your app/models/dummy.rb

class Dummy < ActiveRecord::Base
end

# Replace DummyPlugin with name of engine
engine = Rails::Application::Railties.engines.find { |e| e.class == DummyPlugin::Engine }
dummy_source = File.read File.join(engine.config.root, "app", "models", "dummy.rb")
dummy_source = dummy_source.gsub(/validates :field, :presence => true.*/, "")
eval dummy_source

If it is regular gem instead of an engine the same concept would apply, just would need to load the source for Dummy from the gem root instead of the engine root.

Answer 4

Wanted to add that, if you're trying to clear validations on a instance of your Model (not the entire model class), don't do my_dummy._validate_callbacks.clear, as that will clear validations on every instance (and future instance) of your Dummy model class.

For just the instance (and if you wanted to reinstate the validations later), try the following:

1. Create a copy of the validate callbacks (if you want to reinstate later): my_dummy_validate_callbacks = my_dummy._validate_callbacks.clone

2. Set the validate callbacks on your instance to empty: my_dummy._validate_callbacks = {}

3. Do what you want on my_dummy validation free!

4. Reinstate the callbacks: my_dummy._validate_callbacks = my_dummy_validate_callbacks

Answer 5

In Rails 4.1,

I was able to do _validate_callbacks.clear. In my case, I wanted all the validations for a gem removed, so I could create my own. I did this in a module that was patched into the class.

Module #Name
   extend ActiveSupport::Concern
   included do
        _validate_callbacks.clear
        #add your own validations now
   end
end

Answer 6

Every Rails validator, pre-defined or custom, is an object, and is expected to respond to #validate(record) method. You can monkey patch or stub this method.

# MyModel.validators_on(:attr1, :attr2, ...) is also useful
validator = MyModel.validators.detect do |v|
  validator_i_am_looking_for?(v)
end

def validator.validate(*_)
  true
end

# In RSpec you can also consider:
allow(validator).to receive(:validate).and_return(true)

Tested in Rails 5.1.

Don't do this unless you understand what you're doing ;)