Check arity for scopes

[dogenpunk]

When using a checkbox on a form to include a named scope in a search, the value of the form element is automatically passed to the scope regardless of whether or not the scope requires a parameter. I think that the arity should be checked before passing arguments.

[ernie]

I agree. I'd be happy to accept a patch with tests for this.

[dogenpunk]

And I would be happy to write said patch & tests. I'm reading through the source now, I'll add a pull request when I've got it sussed. Thanks!

[dogenpunk]

So the problem that I'm running into with this is that scopes are wrapped up in lambdas. So calling arity on a scope always returns -1. I'm not really sure how to get at the inner lambda to check. Any ideas? Or would it be better/easier to pass some config in the search_methods method?

[dogenpunk]

The other option that just dawned on me is to define the scope using Proc to skirt the argument checking. But I feel dirty suggesting it.

[ernie]

Yeah, that actually occurred to me when you mentioned it -- seems sloppy but would work just fine.

[ernie]

@dogenpunk any progress on a pull request?

[dogenpunk]

Not much actually. I think this is actually an issue with the implementation of scope in Rails, but I haven't been able to figure out how that would have to change in order to expose the arity. And after some thought, the idea of passing in a param to define the number of required parameters in the search_methods method seems like a bad idea. I'll open an issue with the Rails team and see if I can get some feedback.

[ernie]

OK. I'll close this one for now, but happy to reopen if things get sorted on the core side.

[gamov]

mmm, so this is the root of my problem (#86 (comment))
I've been battling with meta_search to add a checkbox to activate or not a scope with a lambda without success.
The only way I find is described in the linked comment.
I think it wouldn't be too bad to add a parameter to the search_methods to specify that the defined methods/scopes can be activated/deactivated by a checkbox...

Ok, the workaround i found is not satisfactory, but works. It doesn't help scopes created by gems:

 scope :with_qty, lambda { |*p| where(:id.lt => 100) }
  search_methods :with_qty,  :validator => Proc.new {|cb| cb == "1"}

I tried to remove the parameter completely with :formatter => Proc.new {|param| nil} but it doesn't work.
Any help?

[afurmanov]

It is possible to patch named scopes in Rails 3, so they would return a correct arity, here is an example: https://gist.github.com/4659655. The patch works for named scopes with arity 0 and 1, tough it is refactorable to be more general.

[hachpai]

Hello! I had the same expect for fiterrific. I've made a fork. As arity for scope and enums doesn't work as expected I use the ArgumentError exception.

filterrific_available_filters.each do |filter_name|
    filter_param = filterrific_param_set.send(filter_name)
      next if filter_param.blank? # skip blank filter_params
      begin
        ar_rel = ar_rel.send(filter_name, filter_param)
      rescue ArgumentError #if we have a scope with arity 0 or enum query, we can perform the request without the parameter
        ar_rel = ar_rel.send(filter_name) if (filter_param == 1)
      end
    end
    ar_rel
end