Django admin - make all fields readonly

Since django 2.1, you can prevent editing, while allowing viewing, by returning False from the ModelAdmin's has_change_permission method, like this:

class CustomAdmin(admin.ModelAdmin):
    def has_change_permission(self, request, obj=None):
        return False

(This will not work before django 2.1, as it will also deny permission to any user trying only to view.)

Careful, self.model._meta.fields are not necessarily the same fields that CustomAdmin has!

"All fields of the Admin" would look more like this:

from django.contrib import admin
from django.contrib.admin.utils import flatten_fieldsets

class CustomAdmin(admin.ModelAdmin):
    def get_readonly_fields(self, request, obj=None):
        if request.user.is_superuser:
            return self.readonly_fields

        if self.declared_fieldsets:
            return flatten_fieldsets(self.declared_fieldsets)
        else:
            return list(set(
                [field.name for field in self.opts.local_fields] +
                [field.name for field in self.opts.local_many_to_many]
            ))

Ok, now there's this:

class CustomAdmin(admin.ModelAdmin):
    def get_readonly_fields(self, request, obj=None):
        # ...

        return [f.name for f in self.model._meta.fields]

Still looking for a less ugly way.