ReadOnly ModelAdmin

class ReadOnlyAdmin(admin.ModelAdmin):
    def has_add_permission(self, request):
        return False

    def has_delete_permission(self, request, obj=None):
        return False

    def get_readonly_fields(self, request, obj=None):
        if obj:
            return self.readonly_fields + tuple(obj.__class__._meta.get_all_field_names())
        return self.readonly_fields