Rails 3 - Pass a parameter to custom validation method

Question

I am looking to pass a value to a custom validation. I have done the following as a test:

validate :print_out, :parameter1 => \'Hello\'

With this

Answer 1

Inside the 'config\initializers\' directory, you can create your own validations. As an example, let's create a validation 'validates_obj_length.' Not a very useful validation, but an acceptable example:

Create the file 'obj_length_validator.rb' within the 'config\intializers\' directory.

ActiveRecord::Base.class_eval do
    def self.validates_obj_length(*attr_names)
        options = attr_names.extract_options!
        validates_each(attr_names, options) do |record, attribute, value|
          record.errors[attribute] << "Error: Length must be " + options[:length].to_s unless value.length == options[:length]
        end
    end
end

Once you have this, you can use the very clean:

validates_obj_length :content, :length => 5

Basically, we reopen ActiveRecord::Base class and implement a new sub-validation. We use the splat (*) operator to accept an array of arguments. We then extract out the hash of options into our 'options' variable. Finally we implement our validation(s). This allows the validation to be used with any model anytime and stay DRY!