Override error in certain contexts

src/registrar/forms/portfolio.py

@@ -300,6 +300,29 @@ class BasePortfolioMemberForm(forms.ModelForm):
 
         return cleaned_data
     
+    def _post_clean(self):
+        """
+        Override _post_clean to customize model validation errors.
+        This runs after form clean is complete, but before the errors are displayed.
+        """
+        try:
+            super()._post_clean()
+            self.instance.clean()
+        except forms.ValidationError as e:
+            override_error = False
+            if hasattr(e, "code"):
+                field = "email" if "email" in self.fields else None
+                if e.code == "has_existing_permissions":
+                    self.add_error(field, "This user is already a member of another .gov organization.")
+                    override_error = True
+                elif e.code == "has_existing_invitations":
+                    self.add_error(field, "This user has already been invited to another .gov organization.")
+                    override_error = True
+
+            if override_error:
+                if "__all__" in self._errors:
+                    del self._errors["__all__"]
+
     def map_instance_to_initial(self):
         """
         Maps self.instance to self.initial, handling roles and permissions.

src/registrar/models/utility/portfolio_helper.py

@@ -285,7 +285,8 @@ def validate_user_portfolio_permission(user_portfolio_permission):
         if existing_permissions.exists():
             raise ValidationError(
                 "This user is already assigned to a portfolio. "
-                "Based on current waffle flag settings, users cannot be assigned to multiple portfolios."
+                "Based on current waffle flag settings, users cannot be assigned to multiple portfolios.",
+                code="has_existing_permissions"
             )
 
         existing_invitations = PortfolioInvitation.objects.filter(email=user_portfolio_permission.user.email).exclude(
@@ -295,7 +296,8 @@ def validate_user_portfolio_permission(user_portfolio_permission):
         if existing_invitations.exists():
             raise ValidationError(
                 "This user is already assigned to a portfolio invitation. "
-                "Based on current waffle flag settings, users cannot be assigned to multiple portfolios."
+                "Based on current waffle flag settings, users cannot be assigned to multiple portfolios.",
+                code="has_existing_invitations"
             )
 
 
@@ -343,6 +345,7 @@ def validate_portfolio_invitation(portfolio_invitation):
 
     # == Validate the multiple_porfolios flag. == #
     user = User.objects.filter(email=portfolio_invitation.email).first()
+
     # If user returns None, then we check for global assignment of multiple_portfolios.
     # Otherwise we just check on the user.
     if not flag_is_active_for_user(user, "multiple_portfolios"):
@@ -355,13 +358,15 @@ def validate_portfolio_invitation(portfolio_invitation):
         if existing_permissions.exists():
             raise ValidationError(
                 "This user is already assigned to a portfolio. "
-                "Based on current waffle flag settings, users cannot be assigned to multiple portfolios."
+                "Based on current waffle flag settings, users cannot be assigned to multiple portfolios.",
+                code="has_existing_permissions"
             )
 
         if existing_invitations.exists():
             raise ValidationError(
                 "This user is already assigned to a portfolio invitation. "
-                "Based on current waffle flag settings, users cannot be assigned to multiple portfolios."
+                "Based on current waffle flag settings, users cannot be assigned to multiple portfolios.",
+                code="has_existing_invitations"
             )