Declarative ruby programming replacement for if/then/else/RETURN/end?

Question

I have this showing up all over in my controllers:

if not session[:admin]
  flash[:notice] = "You don't have the rights to do #{:action}."
  redirect_to :action=>:index
  return
end

And its sibling:

if not session[:user] and not session[:admin]
  flash[:notice] = "You don't have the rights to do #{:action}."
  redirect_to :action=>:index
  return
end

I would like to reduce this all down to a single declarative line when I want to use it in a method:

def action_which_requires_rights
    require_rights :admin
    #or:
    #:require_rights :user_or_admin
end

Clearly, if require_rights fails, I don't want the rest of the method executed. I would swear that there was a way to do this, but I can't find where I read about it. Am I imagining this?

Answer 1

Firstly you can do: unless session[:admin] instead of if not ...

Then you can have a before filter which calls your method, this method would do your redirect_to "url" and return.

I have a question, I hope you are not just storing the id of the admin in a session as your the only means of authentication, having an attribute on your user model and querying that might be a safer bet.

Answer 2

As others have said, a before_filter seems like the right tool here. But I'll address the actual pattern you were asking about.

Unfortunately, a method can't cause its calling method to return. The two closest matches to the pattern you are looking for:

A block:

def require_rights(rights)
  if session[rights]
    yield
  else
    flash[:notice] = "You don't have the rights to do #{:action}."
    redirect_to :action=>:index
  end
end

So with that you'd do:

def action_which_requires_rights
  require_rights :admin do
    #do whatever here
  end
end

Or a return value:

def require_rights(rights)
  return true if session[rights]
  flash[:notice] = "You don't have the rights to do #{:action}."
  redirect_to :action=>:index
  false
end

So with that you'd do:

def action_which_requires_rights
  require_rights :admin or return
  #do whatever here
end

I like the block better because it fits in with similar methods, and making the caller do or return feels kind of unnatural to me.