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

class Dummy < ActiveRecord::Base
  validates :field, :presence => true 
end

Now I want to change that to optional using instance_eval (or any other method, really):

Dummy.instance_eval do
  ...
end

What would be the proper syntax to remove the validation, so the field is optional. I would rather do this directly on the model layer, instead doing weird hacks in controllers or views. The use of instance_eval is not really required, but as far as开发者_JS百科 I know, this is generally the best way to enhance classes in Rails.

Edit #1

In general - the original class is part of the gem and I don't want to fork it, nor tie to specific release. The general cause is not really important. Simply editing the original model has far worse consequences than monkey patching.

I found a solution, not sure how solid it is, but it works well in my case. @aVenger was actually close with his answer. It's just that the _validators accessor contains only information used for reflection, but not the actual validator callbacks! They are contained in the _validate_callbacks accessor, not to be confused with _validations_callbacks.

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

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

This will remove all validators for :field. If you want to be more precise, you can reject the specific validator for _validators which is the same as the raw_filter accessor of validate callbacks.

I think this is the most actual solution at this moment (I'm using rails 4.1.6):

# Common ninja
class Ninja < ActiveRecord::Base
  validates :name, :martial_art, presence: true
end

# Wow! He has no martial skills
Ninja.class_eval do
  _validators[:martial_art]
    .find { |v| v.is_a? ActiveRecord::Validations::PresenceValidator }
    .attributes
    .delete(:martial_art)
end

Easest way to remove all validations:

clear_validators!

As I was trying to do this to remove the phone validation from the spree Address model, below is the code I got to work. I added the type check for callback.raw_filter because I only wanted to remove the presence validator on the phone field. I also had to add it because it would fail when trying to run against one of the other validators specified in the Spree::Address model that did not have an 'attributes' key for callback.raw_filter, thus an exception was thrown.

Spree::Address.class_eval do

   # Remove the requirement on :phone being present.
  _validators.reject!{ |key, _| key == :phone }

  _validate_callbacks.each do |callback|
    callback.raw_filter.attributes.delete :phone if callback.raw_filter.is_a?(ActiveModel::Validations::PresenceValidator)
  end

end

I had a similar problem and was able to get past it using:

class MyModel << Dummy
  # erase the validations defined in the plugin/gem because they interfere with our own
  Dummy.reset_callbacks(:validate)
  ...
end

This is under Rails 3.0. The caveat: It does remove ALL validations, so if there are others you want to keep you could try Dummy.skip_callback(...), but I could not figure out the right incantation of arguments to make that work.

One solution is to extend validates :

#no need of instance_eval just open the class
class Dummy < ActiveRecord::Base
  #validates :field, :presence => true 

  def self.validates(*attributes)
    if attributes.first == :field #=> add condition on option if necessary
      return # don't validate
    else
      super(*attributes) #let normal behavior take over
    end
  end
end

And no that's not monkey-patching but extending or decorating a behavior. Rails 3.1 is built on the idea of "multi- inheritance" with module inclusion, specifically to allow this kind agility.

update #2

One caveat is you must load the class with the redefined validates method before the gem containing the call to validates. To do so, require the file in config/application.rb after require "rails/all" as suggested in the railsguides. Something like that :

require File.expand_path('../boot', __FILE__)

require 'rails/all' # this where rails (including active_record) is loaded
require File.expand_path('../dummy' __FILE__) #or wherever you want it

#this is where the gems are loaded...
# the most important is that active_record is loaded before dummy but...
# not after the gem containing the call to validate :field
if defined?(Bundler)
  Bundler.require *Rails.groups(:assets => %w(development test))
end

Hope it works now!

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.

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.

If you doesn't want to make any changes in Parent class then first clear all validations in child class and copy all required validation from parent class to child class

  class Dummy < ActiveRecord::Base
      validates :property, presence: true
      validates :value, length: { maximum: 255 }
  end

And override it in child class

Dummy.class_eval do    
  clear_validators!
  validates :property, presence: true
end

If you really want to do this then here would be a good place to start digging: https://github.com/rails/rails/blob/ed7614aa7de2eaeba16c9af11cf09b4fd7ed6819/activemodel/lib/active_model/validations/validates.rb#L82

However, to be honest, inside of ActiveModel is not where I'd be poking with a stick.

If you can edit the constraint on the original model to put an :if => :some_function on it, you can easily change the behavior of the function it calls to return false. I tested this and it works pretty easily:

class Foo < ActiveRecord::Base

  validates :field, :presence => true, :if => :stuff


  attr_accessor :field

  def stuff
      return true;
  end

end

and then somewhere else:

Foo.class_eval {
  def stuff
    false
  end
}

Why not use @dummy.save_without_validation method to skip validations altogether? I prefer do something like this:

if @dummy.valid?
  @dummy.save # no problem saving a valid record
else
  if @dummy.errors.size == 1 and @dummy.errors.on(:field)
    # skip validations b/c we have exactly one error and it is the validation that we want to skip
    @dummy.save_without_validation 
  end
end

You could put this code in your model or in the controller, depending on your needs.

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

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

I'd have to look more into the code and help, but I'm thining it might be possible to inspect the list of validators of the class, and then modify the entry for the validation you want to change to add in an :if => :some_function conditional to it.

You'll need to do it only once for production (so it can be put inside an initializer, but for development you'll need to put it in the model, or somewhere else that will get loaded each time the corresponding model is (perhaps an observer?).

(I'll edit the answer with more information as I come to research it.)

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 ;)

This does not directly answer the question but here's an option you should consider in such a situation: instead of disabling validation, you could set the required fields in a before_validation hook.

Since you don't need those required fields, set them with some dummy data that satisfies the validation and forget about them.

No ugly monkey patching.

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.