option_groups_from_collection_for_select(collection, group_method, group_label_method, option_key_method, option_value_method, selected_key = nil)
Instance Public methods
Returns a string of <option> tags, like
options_from_collection_for_select, but groups them by
<optgroup> tags based on the object relationships of the
arguments.
Parameters:
collection - An array of objects representing the
<optgroup> tags.
group_method - The name of a method which, when call