Rails - Pre select multiple options with grouped_options_for_select

Question

I would like to preselect multiple options when using grouped_options_for_select in rails 4.1

The method signature is

grouped_options_for_select(grouped_options, selected_key= = nil, options = {})

The selected_key only allows a single value which matches exact options. I would like to preselect multiple options since i am using a multi-select. Is there anyway to do this?

Answer 1

You can make selected_key an array of values for exactly your case.

From the documentation:

"selected may also be an array of values to be selected when using a multiple select."

If you look at the source for grouped_options_for_select it just calls options_for_select passing selected_key.