:prompt appearing in collection_select when a records value is expected

Sorry, this may seem like a simple issue, but: I have a collection_select element that is called via ajax from a _updateregions.html.erb file for creating and editing records that looks like:

<%= collection_select(:wine, :wineregionid,  regions,  :wineregionid, :regionname,
                    options = {:selected => :wineregionid, :prompt   => "Select a Region"}
 ) %>

The problem is, when editing an existing record, the prompt is appearing by default instead on the records value. When I remove the :prompt, it works fine... question is, how can I make this work for both the New and Edit case? According to http://api.rubyonrails.org/classes/ActionVie开发者_如何学Pythonw/Helpers/FormOptionsHelper.html I think I'm doing it right....

collection_select(object, method, collection, value_method, text_method, options = {}, html_options = {})

Returns and tags for the collection of existing return values of method for object‘s class. The value returned from calling method on the instance object will be selected. If calling method returns nil, no selection is made without including :prompt or :include_blank in the options hash.

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i think :prompt donot takes a string . it should be true/false or null. try this

    <%= collection_select(:wine, :wineregionid,  regions,  :wineregionid, :regionname,
                options = {:selected => :wineregionid, :prompt   => true) %>