pulseapi/users/admin_group_editing.py

# ==========================================================
#
#  Custom code to add user management in group admin views.
#
#  See  https://stackoverflow.com/questions/39485067
#
# ==========================================================

from django import forms
from django.contrib import admin
from django.contrib.auth import get_user_model
from django.contrib.admin.widgets import FilteredSelectMultiple
from django.contrib.auth.models import Group

User = get_user_model()


# Create ModelForm based on the Group model.
class GroupAdminForm(forms.ModelForm):
    class Meta:
        model = Group
        exclude = []

    # Add the users field.
    users = forms.ModelMultipleChoiceField(
        queryset=User.objects.all(),
        required=False,
        # Use the pretty 'filter_horizontal widget'.
        widget=FilteredSelectMultiple('users', False)
    )

    def __init__(self, *args, **kwargs):
        # Do the normal form initialisation.
        super(GroupAdminForm, self).__init__(*args, **kwargs)
        # If it is an existing group (saved objects have a pk).
        if self.instance.pk:
            # Populate the users field with the current Group users.
            self.fields['users'].initial = self.instance.user_set.all()

    def save_m2m(self):
        self.instance.user_set.set(self.cleaned_data['users'])

    def save(self, *args, **kwargs):
        return super(GroupAdminForm, self).save()


# Create a new Group admin.
class GroupAdmin(admin.ModelAdmin):
    # Use our custom form.
    form = GroupAdminForm
    # Filter permissions horizontal as well.
    filter_horizontal = ['permissions']