feat: add instance for model form

admin_action_tools/admin/form_tool.py

@@ -1,6 +1,6 @@
 import functools
 from importlib import import_module
-from typing import Callable, Dict
+from typing import Callable, Dict, Optional, Type
 
 from django import forms
 from django.contrib.admin import helpers
@@ -80,11 +80,11 @@ def run_form_tool(
         if step == ToolAction.BACK:
             # cancel ask, revert to previous form
             data = tool_chain.rollback()
-            form_instance = form(data)
+            form_instance = self.get_instance(form, data=data, instance=queryset_or_object)
         # First called by `Go` which would not have tool_name in params
         elif step == ToolAction.CONFIRMED:
             # form is filled
-            form_instance = form(request.POST)
+            form_instance = self.get_instance(form, data=request.POST, instance=queryset_or_object)
             if form_instance.is_valid():
                 metadata = self.__get_metadata(form)
                 tool_chain.set_tool(tool_name, form_instance.data, metadata=metadata)
@@ -93,14 +93,22 @@ def run_form_tool(
             # forward to next
             return func(self, request, queryset_or_object)
         else:
-            form_instance = form()
+            form_instance = self.get_instance(form, instance=queryset_or_object)
 
         queryset: QuerySet = self.to_queryset(request, queryset_or_object)
         context = self.build_context(request, func, queryset, form_instance, tool_name, display_queryset)
 
         # Display form
         return self.render_action_form(request, context)
 
+    @staticmethod
+    def get_instance(
+        form: Type[forms.BaseForm], data: Optional[dict] = None, instance: Optional[forms.BaseForm] = None
+    ) -> forms.BaseForm:
+        if issubclass(form, forms.ModelForm):  # pylint: disable=E721
+            return form(data, instance=instance)
+        return form(data)
+
 
 def add_form_to_action(form: Form, display_queryset=True):
     """

admin_action_tools/tests/unit/form-tool/test_form_action.py

@@ -1,6 +1,10 @@
+from unittest import mock
+
+from django import forms
 from django.contrib.auth.models import User
 from django.urls import reverse
 
+from admin_action_tools.admin.form_tool import ActionFormMixin
 from admin_action_tools.constants import CONFIRM_FORM
 from admin_action_tools.tests.helpers import AdminConfirmTestCase
 from tests.factories import InventoryFactory, ShopFactory
@@ -77,3 +81,26 @@ def test_form_action_with_not_valid_form(self):
 
         self.assertIn("Configure the", response.rendered_content)
         self.assertIn("This field is required.", response.rendered_content)
+
+    def test_get_instance_with_model_form(self) -> None:
+        form_data = mock.MagicMock(spec=dict)
+        model_instance = mock.MagicMock()
+
+        model_form_class = forms.modelform_factory(ShopFactory, forms.ModelForm)
+        form_instance = ActionFormMixin.get_instance(model_form_class, data=form_data, instance=model_instance)
+
+        self.assertIsInstance(form_instance, model_form_class)
+        self.assertEqual(form_instance.data, form_data)
+        self.assertEqual(form_instance.instance, model_instance)
+        self.assertIsInstance(form_instance, model_form_class)
+
+    def test_get_instance_with_form(self) -> None:
+        form_data = mock.MagicMock(spec=dict)
+
+        form_class = forms.Form
+        form_instance = ActionFormMixin.get_instance(form_class, data=form_data)
+
+        self.assertIsInstance(form_instance, form_class)
+        self.assertEqual(form_instance.data, form_data)
+        self.assertFalse(hasattr(form_instance, "instance"))
+        self.assertIsInstance(form_instance, form_class)