Question

In a plugin I am writing I am using alias to override one of the default Rails validators like so:

# Alias the original validator so it's still available under a different name
alias original_validates_uniqueness_of :validates_uniqueness_of unless method_defined?(:original_validates_uniqueness_of)
# Then alias the custom validator under the original name
alias validates_uniqueness_of :custom_validates_uniqueness_of

This all works pretty well. When “validates_uniqueness_of” is defined on an attribute in a AR model, it will use my “custom_validates_uniqueness_of” method instead. Validations are running as expected.

However, when I call:

SomeARclass.respond_to?(:validates_uniqueness_of)

..it will return false. This behavior will mess with several popular plugins.

My question:
Why is respond_to returning “false”? Is this behavior the result of alliasing? How can adjust my custom validator to make it return true?

Thank you for your help.
Erwin

Answer 1

Your sample, on the surface, looks like it should work. I expect you’ve found that, inside of the class body for class SomeARclass, you actually can call validates_uniqueness_of.

class SomeARclass
  validates_uniqueness_of :first_field # works
end

However, I expect that scoped_validates_uniqueness_of is a private method. That’s why you have been unable to send that message to SomeARclass from outside of its class body.

SomeARclass.validates_scoped_uniqueness_of :first_field # fails
#=> NoMethodError: private method "validates_scoped_uniqueness_of" called
    for SomeARclass:Class

When you alias a private method with a new name, such as aliasing the private method validates_scoped_uniqueness_of with the new name validates_uniqueness_of, then that new method is also private. I expect that’s what happened here.

The documentation for #respond_to? reads:

- (Boolean) respond_to?(symbol, include_private = false)

Returns true if obj responds to the given method. Private methods are included in the search only if the optional second parameter evaluates to true.