rails select tag with multiple values pre selected

Question

I am trying to have a multiple select box. select box will contain all the stores in the DB but the ones that the user belongs to will be selected.

I'm half way there. I got a select box which has all the stores in the database. I'm unable to select the ones that the user belongs to.

I have the following:

<%= select_tag 'stores[]', options_for_select(@stores.map {|s| [s.store_name, s.store_id]}, 
:selected => @user.stores.map {|j| [j.store_name, j.store_id]}), :multiple => true, :size => 
10 %>

I have a map with stores that a user belongs to. it is in:

@user.stores

Answer 1

after a fair amount of trial and error the following worked for me:

<%=select_tag 'stores[]', options_for_select(
@stores.map {|s| [s.store_name, s.store_id]}, 
@user.stores.map {|j| j.store_id}
), :multiple => true, :size => 10%>