fix(home/models.py): fix allowed_groups not changing in wagtail panel

home/models.py

@@ -1,8 +1,9 @@
 from django.contrib.auth.models import Group
-from django.db import models
+from django.forms import CheckboxSelectMultiple
 from wagtail.admin.panels import FieldPanel
 from wagtail.fields import RichTextField
 from wagtail.models import Page
+from wagtail.models.copying import ParentalManyToManyField
 
 
 class HomePage(Page):
@@ -13,18 +14,15 @@ class HomePage(Page):
 
 class CoursePage(Page):
     body = RichTextField(blank=True)
-    allowed_groups = models.ForeignKey(
+    allowed_groups = ParentalManyToManyField(
         Group,
-        null=True,
-        blank=True,
-        on_delete=models.SET_NULL,
         related_name="course_pages",
         help_text="Select a group to restrict access to this course. Non-members will be prompted to purchase the course to view modules.",
     )
 
     content_panels = Page.content_panels + [
         FieldPanel("body"),
-        FieldPanel("allowed_groups", heading="Allowed Groups"),
+        FieldPanel("allowed_groups", widget=CheckboxSelectMultiple),
     ]