Rails: Multi-select box syntax

Question

Basically I have this form:

<%= builder.select(:song_id, options_for_select(@selections.sort!), {}, {multiple: true, size: 7}) %>

Which in the html is rendering something like this:

<input name="allocation[song_id][]" type="hidden" value="" />
<select id="allocation_song_id" multiple="multiple" name="allocation[song_id][]" size="7">

Basically I'm curious as to where the second set of array brackets (allocation[song_id]**[]**) comes from, as I think it's affecting the way my arguments are passing (the song id keeps defaulting to the first song upon form submission). Any pointers would be much appreciated.

Answer 1

Multiple select box is like checkbox. If you can select more than one option, then it should be array (brackets are array). Hidden input is when no one is selected.