Schienen: Ändern Sie den Index basierend auf dem ausgewählten Wert im Dropdown-Menü

Ich habe zwei Modelle:

class Location < ActiveRecord::Base
    has_many :cows
    accepts_nested_attributes_for :cows
end

class Cow < ActiveRecord::Base
    belongs_to :location
end

Jeder Standort hat eine ID, einen Namen und drei boolesche Werte. Eine Kuh besteht aus einer ID, zwei Strings und zwei Daten und enthält auch eine location_id.

In meiner Kuhansicht habe ich eine Dropdown-Liste mit jedem Standort. Es wird automatisch aktualisiert, wenn ich einen Standort erstelle, bearbeite oder lösche.

Unter dem Dropdown sehen Sie alle jemals angelegten Kühe. Danach gibt es ein Formular zum Hinzufügen einer neuen Kuh mit den beiden Stringfeldern und zwei Datumsfeldern.

Now I want two things: Whenever I select a value in the dropdown, the displayed cows should change. If I select for example location 2, only cows that have a location_id = 2 in the table should be shown. Also when I create a new cow, the id of the selected location should be saved as well (in this example location_id = 2 should be saved in the cow row when I click the button at the very bottom).

This is how the dynamic dropdown looks like in the cow index.html file:

  <%= simple_form_for Cow.new do |f| %>
    <%= f.collection_select :location, Location.order('name').all, :id, :name, { prompt: "Ort auswählen" } %>
  <% end %>

And this is my cow controller:

  def index
    if (params[:location] && Location.all.collect(&:name).include?(params[:location][:name]))
     @cows = Cow.send(params[:location][:name].downcase)
    else
     @cows = Cow.all
    end
  end

  # (...)

  def create
    @cow = Cow.new(cow_params)
    # (...)
  end

  private
    # Use callbacks to share common setup or constraints between actions.
    def set_cow
      @cow = Cow.find(params[:id])
    end

    # Never trust parameters from the scary internet, only allow the white list through.
    def cow_params
      params.require(:cow).permit(:ohrmarke, :hin, :weg, :stallnummer, :location_attributes => [:id])
    end
end

The edited index part just does not work. Perhaps because I have a dropdown for Cow.new and I don't have a submit button. Now the thing is: I need the dropdown (value) for a new cow but also want to display cows that fit to the selected dropdown value. Also I don't want to use a submit button just for the dropdown box. Is there any solution for my problem? I googled so much but just can't find the right answer for my problem.

Edit: I edited my cows controller and my index page: cow controller:

def index
    @locations_all = Location.all
    if (params[:location] && cows = Cow.where(location_id: params[:location]))
      @cows = cows
      @location = Location.where(id: params[:location])
    else
      @cows = Cow.all
    end
end

# (...)

def create
  @cow = Cow.new(cow_params)
  # (...)
end

private
  # Use callbacks to share common setup or constraints between actions.
  def set_cow
    @cow = Cow.find(params[:id])
  end

  # Never trust parameters from the scary internet, only allow the white list through.
  def cow_params
    params.require(:cow).permit(:ohrmarke, :hin, :weg, :stallnummer, :location_attributes => [:id])
  end

cow index.html:

  <%= simple_form_for Cow.new do |f| %>
    <%= f.collection_select :location, Location.order('name').all, :id, :name, { prompt: "Ort auswählen" } %>
    <ul>
      <% @locations_all.each do |loc| %>
        <li><%= link_to loc.name, @cows.index(location: loc.id) %></li>
      <% end %>
    </ul>


    <%= f.hidden_field :location_id, value: @location_id %>

    <table class="striped">
      <thead class="thead-default">
        <tr>
          <th>Ohrmarke</th>
          <th>Stallnr.</th>
          <th>Hin/Weg</th>
        </tr>
      </thead>
      <tbody>
        <!-- ... -->
      </tbody>
    </table><br>

    <%= f.input :ohrmarke, as: :string, input_html: { maxlength: 5 } %>
    <%= f.input :stallnummer, as: :string, input_html: { maxlength: 3 } %>

    <!-- datepicker not functional yet -->
    <input type="date" class="datepicker" id="hin" placeholder="hin">
    <input type="date" class="datepicker" id="hin" placeholder="weg">

    <button class="btn waves-effect waves-light" type="submit" name="action">Zuordnung speichern
      <i class="material-icons right">send</i>
    </button>
  <% end %>