Improve rendering of ManyToManyField values (or any other property / attribute that returns a Manager) in InspectView (#3423)

* Fix for #3298
* Improve rendering of ManyToManyField values (or any other property / attribute that returns a Manager) in InspectView

wagtail/contrib/modeladmin/tests/test_page_modeladmin.py

@@ -4,7 +4,7 @@ from django.contrib.auth import get_user_model
 from django.contrib.auth.models import Group, Permission
 from django.test import TestCase
 
-from wagtail.tests.testapp.models import BusinessIndex
+from wagtail.tests.testapp.models import BusinessIndex, EventCategory, EventPage
 from wagtail.tests.utils import WagtailTestUtils
 from wagtail.wagtailcore.models import GroupPagePermission, Page
 
@@ -125,6 +125,29 @@ class TestInspectView(TestCase, WagtailTestUtils):
         response = self.get(4)
         self.assertContains(response, 'Christmas', 2)
 
+    def test_manytomany_output(self):
+        """
+        Because ManyToMany fields are output InspectView by default, the
+        `categories` for the event should output as a comma separated list
+        once populated.
+        """
+        eventpage = EventPage.objects.get(pk=4)
+        free_category = EventCategory.objects.create(name='Free')
+        child_friendly_category = EventCategory.objects.create(name='Child-friendly')
+        eventpage.categories = (free_category, child_friendly_category)
+        eventpage.save()
+        response = self.get(4)
+        self.assertContains(response, '<dd>Free, Child-friendly</dd>', html=True)
+
+    def test_false_values_displayed(self):
+        """
+        Boolean fields with False values should display False, rather than the
+        value of `get_empty_value_display()`. For this page, those should be
+        `locked`, `expired` and `has_unpublished_changes`
+        """
+        response = self.get(4)
+        self.assertContains(response, '<dd>False</dd>', count=3, html=True)
+
     def test_location_present(self):
         """
         The location should appear once, in the field listing

wagtail/contrib/modeladmin/views.py

@@ -861,6 +861,14 @@ class InspectView(InstanceSpecificView):
         # we can render something useful. raises AttributeError appropriately.
         val = getattr(self.instance, field_name)
 
+        if isinstance(val, models.Manager):
+            val = val.all()
+
+        if isinstance(val, models.QuerySet):
+            if val.exists():
+                return ', '.join(['%s' % obj for obj in val])
+            return self.model_admin.get_empty_value_display(field_name)
+
         # wagtail.wagtailimages might not be installed
         try:
             from wagtail.wagtailimages.models import AbstractImage
@@ -880,7 +888,9 @@ class InspectView(InstanceSpecificView):
             pass
 
         # Resort to returning the real value or 'empty value'
-        return val or self.model_admin.get_empty_value_display(field_name)
+        if val or val is False:
+            return val
+        return self.model_admin.get_empty_value_display(field_name)
 
     def get_image_field_display(self, field_name, field):
         """ Render an image """