Трясогузка Как получить стоимость заказываемого предмета

Я относительный новичок в программировании Wagtail. Моя попытка - каскадное приложение, где заголовок формируется из отношения к нижележащему элементу. Каскад должен быть структурирован следующим образом Fach --> Reihe --> Ebene --> Behaelter Мой models.py

from django.db import models
from django.utils.text import slugify
from wagtail.models import Page
from wagtail.admin.panels import FieldPanel  # InlinePanel  # PageChooserPanel
from django import forms
from wagtail.admin.forms import WagtailAdminPageForm
from django.utils.translation import gettext_lazy as _
# Create your models here.


class NoTitleForm(WagtailAdminPageForm):
    title = forms.CharField(required=False, disabled=True, help_text=('Title is autogenerated'))
    slug = forms.CharField(required=False, disabled=True, help_text=('Slug is autogenerated'))

    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)
        if not self.initial['title']:
            self.initial['title'] = _('auto-generated-title')
        if not self.initial['slug']:
            self.initial['slug'] = _('auto-generated-slug')


class ReihePage(Page):
    base_form_class = NoTitleForm

    content_panels = [
        MultiFieldPanel(
            [
                InlinePanel("Fach", label="Fach", min_num=0, max_num=10),
            ]
                      ),

        FieldPanel('title'),
        FieldPanel('slug'),
        ]

    def clean(self):
        super().clean()
        new_title = "anzahl from Fach" + "title from Fach" <--** How to get the values from the InlinePanel**
        
        self.title = new_title
        self.slug = slugify(new_title) 



class ReihePageOrderable(Orderable):
    page = ParentalKey(ReihePage, related_name="Fach", null=True)
    fach = models.ForeignKey("Fachpage", on_delete=models.SET_NULL, null=True)
    anzahl = models.IntegerField(default=1)
    
    
class FachPage(Page):
    laenge = models.IntegerField(null=True, blank=True, verbose_name='Länge in mm')
    breite = models.IntegerField(null=True, blank=True, verbose_name='Breite in mm')

    content_panels = [
        # FieldPanel('bezeichnung'),
        FieldPanel('laenge'),
        FieldPanel('breite'),
        FieldPanel('title'),
        FieldPanel('slug'),
        ]

    parent_page_types = ['FachIndexPage']

    class Meta:
        unique_together = ('laenge', 'breite')

    def clean(self):
        """Override the values of title and slug before saving."""
        super().clean()
        a = str(self.laenge)
        b = str(self.breite)
        new_title = "Fach" + " " + a + "x" + b + " mm"
        self.title = new_title
        self.slug = slugify(new_title)
    base_form_class = NoTitleForm


class FachIndexPage(Page):
    def get_context(self, request, *args, **kwargs):
        context = super().get_context(request, *args, **kwargs)

        context['Fächer'] = FachPage.objects.all()
        return context

    subpage_types = ['FachPage']

Я читаю документацию на сайте wagtail. Я пробую функцию с get_context и многое другое

class ReihePage(Page):
    base_form_class = NoTitleForm

    content_panels = [
        MultiFieldPanel([
            InlinePanel("fach_relation", label="Fach", min_num=0, max_num=10),
        ]),
        FieldPanel('title'),
        FieldPanel('slug'),
    ]

    def clean(self):
        super().clean()
        fach_instances = self.fach_relation.all()
        fach_count = len(fach_instances)
        fach_titles = [fach_instance.title for fach_instance in fach_instances]
        new_title = f"Count from Fach: {fach_count}, Titles: {', '.join(fach_titles)}"
        self.title = new_title
        self.slug = slugify(new_title)


class ReihePageOrderable(Orderable):
    page = ParentalKey(ReihePage, related_name="fach_relation")
    fach = models.ForeignKey("FachPage", on_delete=models.SET_NULL, null=True)
    anzahl = models.IntegerField(default=1)