Select2 multiple rails form value format？

Question

I'm using Select2 3.5.2 with a Rails 2.3 app using Postgres and have a form field with multiple: true

$('.select2').select2()

<%= f.collection_select :user_ids, User.all, :id, :name, class: 'select2', multiple: true, %>

When saving, the database is populated with (for example):

--- 
- ""
- "4"
- "7"

But when editing the form, the values do not populate the select2. I have tried passing multiple kinds of values into the select to try to populate it, but no luck. I've tried:

value: "--- \n- ""\n- "4"\n- "7""
value: 4,7
value: [4,7]
value: ['4', '7']
value: "[\"4\", \"7\"]"

What value does it expect so that it can be populated with existing values?

Answer 1

Ok, I figured it out. I was putting the value in the wrong place. Instead of:

<%= f.collection_select :user_ids, User.all, :id, :name, class: 'select2', multiple: true, value: [1] %>

I needed:

<%= f.select :user_ids, options_from_collection_for_select(User.all, :id, :name, params[:user_ids] || [1,2]), class: 'select2', multiple: true %>

At least, that worked for me.