title: dynamic filtering with dropdown menu
body: <p>I have the following model:</p>
  
  <pre><code>class Rate(models.Model):
      building = models.ForeignKey(Building, verbose_name="Objekt")
      year = models.IntegerField("Jahr")
      monthly_rate = models.DecimalField("Monatsrate", max_digits=8, decimal_places=2)
      paid = models.DecimalField("Tatsächlich Bezahlt (Brutto)", max_digits=8, decimal_places=2, blank=True, null=True)
  
  class Building(models.Model):
      customer = models.ForeignKey(Customer, verbose_name="Kunde")
      ...
      billing_begin = models.DateField("Abrechnungsbeginn")
  
  class Bank(models.Model):
      name = models.CharField("Bankname", max_length=64) #Bankname
      account_number = models.IntegerField("Kontonummer") #Kontonummer
      code_number = models.IntegerField("Bankleitzahl") #Bankleitzahl
      IBAN = models.CharField(max_length=32)
      BIC = models.CharField(max_length=32)
  
  class Customer(models.Model):
      bank = models.ForeignKey(Bank)
  </code></pre>
  
  <p>Now I have the following view:</p>
  
  <pre><code>class BuildingRateListView(ListView):
      model = Building
      template_name = "Building/building_bank_list.html"
  
      def get_context_data(self, **kwargs):
          context = super(BuildingRateListView, self).get_context_data(**kwargs)
          buildings = Building.objects.filter(customer__debitor=True).order_by('customer__bank', 'customer__last_name')
  
      erg = []
      for b in buildings:
          rate = str(b.rate_set.latest('year')) + "€"
          erg.append(rate)
  
      context['building_list'] = erg
      banklist = []
      for b in Bank.objects.all():
          bank_list.append(b)
          #some other code here
  
      context['bank_list'] = bank_list
      return context
  </code></pre>
  
  <p>In my template I have a List of my buildings and a Dropdown with the list of banks.
  In the Dropdown I want to select a Bank and show only those Buildings, where the Customer hast the selected bank.
  As a beginner I don't know how to make this dynamic query. How to write in my view.py, urls.py and template.html?</p>