Rails 5: collection_select not saving

My form have collection select but no saving to database Form tryings assign player id to "pretender" record

http://ift.tt/2sL2jfR

database models:

 create_table "players", force: :cascade do |t|
    t.string "name"
    t.string "group"
    t.text "info"
    t.datetime "created_at", null: false
    t.datetime "updated_at", null: false
  end

  create_table "pretenders", force: :cascade do |t|
    t.string "name"
    t.string "archtype"
    t.string "magic"
    t.string "scale"
    t.integer "player_id"
    t.datetime "created_at", null: false
    t.datetime "updated_at", null: false
  end

in form partial:

 <div class="field">
        <%= form.label :player_id %>
        <%= form.collection_select(:player_id, Player.all, :id, :name, {}, {:multiple => true, :size => '10'}) %>
      </div>

generated html select options have value but not saving?

    <select multiple="multiple" size="10" name="pretender[player_id][]">
    <option value="1">sy</option>
    <option value="2">malakal</option>
    <option value="3">pigs go moo</option>
    <option value="4">malgrib</option>
    <option value="5">Rael</option>
    <option value="6">Nargo</option>
    <option value="7">salva</option>
    <option value="8">pbiecub</option>
    <option value="9">Jude</option>
    <option value="10">Cirno</option>
</select>

here params at pretender controller:

def pretender_params
  params.require(:pretender).permit(:name, :archtype, :magic, :scale, :player_id)
  params.require(:pretender).permit(:id)
end

Am attempt solution at: Collection_select not saving & other pages, but site won't let me post more links lol