adds validation to constrain the ability to apply for the same positi…

…on twice

backend/samfundet/models/recruitment.py

@@ -578,6 +578,7 @@ def clean(self, *args: tuple, **kwargs: dict) -> None:
         # Don't validate withdrawn applications except for deadline
         if not self.withdrawn and self.applicant_priority:
             self._validate_priority(errors)
+            self._validate_no_duplicate_position(errors)
         if self.recruitment.max_applications:
             self._validate_application_limits(errors)
 
@@ -587,6 +588,18 @@ def clean(self, *args: tuple, **kwargs: dict) -> None:
         if errors:
             raise ValidationError(errors)
 
+    def _validate_no_duplicate_position(self, errors: dict[str, list[str]]) -> None:
+        """
+        Validates that the user hasn't already applied to this position,
+        while allowing updates to existing applications
+        """
+        existing = (
+            RecruitmentApplication.objects.filter(user=self.user, recruitment_position=self.recruitment_position, withdrawn=False).exclude(pk=self.pk).exists()
+        )
+
+        if existing:
+            errors['recruitment_position'].append('You have already applied for this position')
+
     def _validate_priority(self, errors: dict[str, list[str]]) -> None:
         """
         Validates that the application's priority is within allowed bounds.