Rails的生存时间可变

Question

In the standard "index" method of controller I set some value in the params hash in order to use it in the view if it's not initialized yet in other case do nothing.

def index
  params[:my_value] ||= {}
end

when I use include? method on the params[:my_value] in the view, there's an error evaluating nil.include?

Why there's such error if params[:my_value] cannot be nil. If it's nil, its value should be initialized with {}, that's what ||= operator does. What can be the problem here?

Answer 1

The solution was in the merge method. It turned out that

a = b.merge(a) 

and

a.merge(b) {|key, v1, v2| v1 }

do different things and in the first case(which was wrong) nil appears somewhere. I haven't figured out yet why is it so because merge method always return a hash and when I replaced the first variant with the second everything was ok. So I don't see any problem...

Answer 2

rails parameters exists upto request flow completes

You can access params inside view page going to be rendered but params will not be available if you are doing re-direction to another page inside controller action as it interrupts request flow.