Prevent deleting contributors voted for in the form (#1651)

Contribution Formset: Hide delete button if entry can not be deleted. Fixes #1558.

evap/evaluation/templates/contribution_formset.html

@@ -66,7 +66,7 @@
                         {% include 'bootstrap_form_errors.html' with errors=form.label.errors %}
                     </td>
                     <td>
-                    {% if editable %}
+                        {% if editable and form.show_delete_button %}
                             {% include 'bootstrap_form_field_widget.html' with field=form.DELETE class="d-none" %}
                         {% endif %}
                     </td>

evap/staff/forms.py

@@ -517,6 +517,16 @@ class ContributionForm(forms.ModelForm):
         if not self.cleaned_data.get("does_not_contribute") and not self.cleaned_data.get("questionnaires"):
             self.add_error("does_not_contribute", _("Select either this option or at least one questionnaire!"))
 
+    @property
+    def show_delete_button(self):
+        if self.instance.pk is None:
+            return True  # not stored in the DB. Required so temporary instances in the formset can be deleted.
+
+        if not self.instance.ratinganswercounter_set.exists() and not self.instance.textanswer_set.exists():
+            return True
+
+        return False
+
 
 class ContributionCopyForm(ContributionForm):
     def __init__(self, data=None, instance=None, evaluation=None, **kwargs):

evap/staff/tests/test_forms.py

@@ -6,6 +6,7 @@ from model_bakery import baker
 
 from evap.contributor.forms import EvaluationForm as ContributorEvaluationForm
 from evap.evaluation.models import (
+    Answer,
     Contribution,
     Course,
     Degree,
@@ -13,7 +14,9 @@ from evap.evaluation.models import (
     Evaluation,
     Question,
     Questionnaire,
+    RatingAnswerCounter,
     Semester,
+    TextAnswer,
     UserProfile,
 )
 from evap.evaluation.tests.tools import (
@@ -554,6 +557,36 @@ class ContributionFormsetTests(TestCase):
         form = CourseForm(instance=course)
         self.assertIn(proxy_user, form.fields["responsibles"].queryset)
 
+    def test_prevent_contribution_deletion_with_answers(self):
+        """
+        When answers for a contribution already exist, it should not be possible to remove that contribution.
+        """
+        self.assertEqual(
+            set(Answer.__subclasses__()),
+            {RatingAnswerCounter, TextAnswer},
+            "This requires an update if a new answer type is added",
+        )
+        evaluation = baker.make(Evaluation)
+        contribution = baker.make(
+            Contribution,
+            evaluation=evaluation,
+            role=Contribution.Role.EDITOR,
+            textanswer_visibility=Contribution.TextAnswerVisibility.GENERAL_TEXTANSWERS,
+            _fill_optional=["contributor"],
+        )
+
+        contribution_formset = inlineformset_factory(
+            Evaluation, Contribution, formset=ContributionFormSet, form=ContributionForm, extra=1
+        )
+        formset = contribution_formset(instance=evaluation, form_kwargs={"evaluation": evaluation})
+        self.assertTrue(formset.forms[0].show_delete_button)
+        self.assertTrue(formset.forms[1].show_delete_button)
+
+        baker.make(RatingAnswerCounter, contribution=contribution)
+
+        self.assertFalse(formset.forms[0].show_delete_button)
+        self.assertTrue(formset.forms[1].show_delete_button)
+
 
 class ContributionFormset775RegressionTests(TestCase):
     """