How do you clear a single entry from a ruby on rails session?

Question

In ruby on rails when doing session[:foo] = nil it leaves an entry named :foo in the session object. How can you get rid of that single entry from the session object?

Answer 1

Actually there is a way to get delete a value from the session. Like RichH said the session variable is a CGI::Session instance. When enter something like session[:foo] it is actually looking that symbol up in a @data instance variable in the session object. That data variable is a hash.

EDIT: There is a data instance variable in the CGI::Session class. If you go to the docs and look at the source code for the []= method you'll see that there is a @data member.

So to delete session[:foo] all you have to do is access that @data variable from inside the session

   session.data[:foo]

Now to delete it:

   session.data.delete :foo

Once you do this the there should be no more foo in your session variable.

Answer 2

It looks like the simplest version works. All stores (Cookie, File, ActiveRecord, ...) use AbstractStore::SessionHash as the object that contains the data, the different stores provide only the means to load and save the AbstractStore::SessionHash instances.

AbstractStore::SessionHash inherits from Hash, so this defers to the Hash#delete method:

session.delete(:key_to_delete)

Answer 3

As the Session is a Ruby CGI::Session and not a Hash, calling delete will actually delete session. Delete takes no parameters - this is my you're getting the "wrong number of arguments (1 or 0)" message when you try what hyuan suggests.

The generally accepted way to clear a session entry is with session[:foo] = nil as you suggest. It is far from ideal, but statements like session[:foo].nil? will behave as expected.

I really wish it behaved like a normal Hash ... but it doesn't.