From inside of a form_for in rails, I'm inserting multiple select values into the database, like this:

<div class="new-partner-form">
<%= form_for [:admin, matching_profile.partner, matching_profile],  :html => {:id => "edit_profile", :multipart => true} do |f| %>
<%= f.submit "Submit", :class => "hidden" %>    
  <div class="rounded-block quarter-wide radio-group">
    <h4>Exclude customers from source:</h4>
     <%= f.select :source, User.select(:source).group(:source).order(:source).map {|u| [u.source,u.source]}, {:include_blank => false}, {:multiple => true} %>
    <%= f.error_message_on :source %>
  </div>

I'm then trying to pull the value from the database like this:

def does_not_contain_source(matching_profiles)
  Expression.select(matching_profiles, :source) do |keyword|
    Rails.logger.info("Keyword is : " + keyword)
    @customer_source_tokenizer ||= Tokenizer.new(User.select(:source).where("id = ?", self.owner_id).map {|u| u.source}[0]) #User.select("source").where("id = ?", self.owner_id).to_s)
    @customer_source_tokenizer.divergent?(keyword)
  end
end

but getting this:

ExpressionErrors: Bad syntax: --- 
- ""
- B
- ""

this is what the value is in the database but it seems to choke when i access it this way. What's the right way to do this?