Refactor how form errors are handled

- When in doubt, refer to the django docs
- There was a *much* better way (thanks, form.add_error)!
- The anti-pattern was deleted, and lo, there was much rejoicing
- Some other refactoring too

InvenTree/part/models.py

@@ -360,7 +360,7 @@ class Part(MPTTModel):
             # And recursively check too
             item.sub_part.checkAddToBOM(parent)
 
-    def checkIfSerialNumberExists(self, sn):
+    def checkIfSerialNumberExists(self, sn, exclude_self=False):
         """
         Check if a serial number exists for this Part.
 
@@ -369,10 +369,28 @@ class Part(MPTTModel):
         """
 
         parts = Part.objects.filter(tree_id=self.tree_id)
+
         stock = StockModels.StockItem.objects.filter(part__in=parts, serial=sn)
 
+        if exclude_self:
+            stock = stock.exclude(pk=self.pk)
+
         return stock.exists()
 
+    def find_conflicting_serial_numbers(self, serials):
+        """
+        For a provided list of serials, return a list of those which are conflicting.
+        """
+
+        conflicts = []
+
+        for serial in serials:
+            if self.checkIfSerialNumberExists(serial, exclude_self=True):
+                conflicts.append(serial)
+
+        return conflicts
+
+
     def getLatestSerialNumber(self):
         """
         Return the "latest" serial number for this Part.

InvenTree/part/views.py

@@ -445,9 +445,9 @@ class PartDuplicate(AjaxCreateView):
                 confirmed = str2bool(request.POST.get('confirm_creation', False))
 
                 if not confirmed:
-                    form.errors['confirm_creation'] = ['Possible matches exist - confirm creation of new part']
-                    
-                    form.pre_form_warning = 'Possible matches exist - confirm creation of new part'
+                    msg = _('Possible matches exist - confirm creation of new part')
+                    form.add_error('confirm_creation', msg)                    
+                    form.pre_form_warning = msg
                     valid = False
 
         data = {
@@ -575,9 +575,10 @@ class PartCreate(AjaxCreateView):
                 confirmed = str2bool(request.POST.get('confirm_creation', False))
 
                 if not confirmed:
-                    form.errors['confirm_creation'] = ['Possible matches exist - confirm creation of new part']
+                    msg = _('Possible matches exist - confirm creation of new part')
+                    form.add_error('confirm_creation', msg)
                     
-                    form.pre_form_warning = 'Possible matches exist - confirm creation of new part'
+                    form.pre_form_warning = msg
                     valid = False
 
         data = {
@@ -862,7 +863,7 @@ class BomValidate(AjaxUpdateView):
         if confirmed:
             part.validate_bom(request.user)
         else:
-            form.errors['validate'] = ['Confirm that the BOM is valid']
+            form.add_error('validate', _('Confirm that the BOM is valid'))
 
         data = {
             'form_valid': confirmed
@@ -1001,7 +1002,7 @@ class BomUpload(InvenTreeRoleMixin, FormView):
         bom_file_valid = False
 
         if bom_file is None:
-            self.form.errors['bom_file'] = [_('No BOM file provided')]
+            self.form.add_error('bom_file', _('No BOM file provided'))
         else:
             # Create a BomUploadManager object - will perform initial data validation
             # (and raise a ValidationError if there is something wrong with the file)
@@ -1012,7 +1013,7 @@ class BomUpload(InvenTreeRoleMixin, FormView):
                 errors = e.error_dict
 
                 for k, v in errors.items():
-                    self.form.errors[k] = v
+                    self.form.add_error(k, v)
 
         if bom_file_valid:
             # BOM file is valid? Proceed to the next step!