[BUG] Deleting a Customer Breaks Associated Sales Orders

Add special protected deleted company
Fixes #2788

InvenTree/company/migrations/0043_company_is_deleted.py

@@ -0,0 +1,18 @@
+# Generated by Django 3.2.12 on 2022-03-29 22:46
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('company', '0042_supplierpricebreak_updated'),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name='company',
+            name='is_deleted',
+            field=models.BooleanField(default=False, help_text='Is this company a deleted placeholder?', verbose_name='is deleted'),
+        ),
+    ]

InvenTree/company/models.py

@@ -9,7 +9,7 @@ import os
 
 from django.utils.translation import ugettext_lazy as _
 from django.core.validators import MinValueValidator
-from django.core.exceptions import ValidationError
+from django.core.exceptions import ValidationError, PermissionDenied
 
 from django.db import models
 from django.db.models import Sum, Q, UniqueConstraint
@@ -147,6 +147,8 @@ class Company(models.Model):
 
     is_manufacturer = models.BooleanField(default=False, verbose_name=_('is manufacturer'), help_text=_('Does this company manufacture parts?'))
 
+    is_deleted = models.BooleanField(default=False, verbose_name=_('is deleted'), help_text=_('Is this company a deleted placeholder?'))
+
     currency = models.CharField(
         max_length=3,
         verbose_name=_('Currency'),
@@ -266,6 +268,18 @@ class Company(models.Model):
 
         return self.purchase_orders.filter(status__in=PurchaseOrderStatus.FAILED)
 
+    def save(self, *args, **kwargs):
+        """Save the instance, unless it is the magic already deleted object"""
+        if self.pk and self.is_deleted:
+            raise PermissionDenied(_('This company is a placeholder and can not be updated'))
+        return super().save(*args, **kwargs)
+
+    def delete(self, *args, **kwargs):
+        """Delete the instance, unless it is the magic already deleted object"""
+        if self.is_deleted:
+            raise PermissionDenied(_('This company is a placeholder and can not be deleted'))
+        return super().delete(*args, **kwargs)
+
 
 class Contact(models.Model):
     """ A Contact represents a person who works at a particular company.

InvenTree/order/migrations/0064_auto_20220329_2246.py

@@ -0,0 +1,25 @@
+# Generated by Django 3.2.12 on 2022-03-29 22:46
+
+from django.db import migrations, models
+import order.models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('company', '0043_company_is_deleted'),
+        ('order', '0063_alter_purchaseorderlineitem_unique_together'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='purchaseorder',
+            name='supplier',
+            field=models.ForeignKey(help_text='Company from which the items are being ordered', limit_choices_to={'is_supplier': True}, on_delete=models.SET(order.models.get_deleted_company), related_name='purchase_orders', to='company.company', verbose_name='Supplier'),
+        ),
+        migrations.AlterField(
+            model_name='salesorder',
+            name='customer',
+            field=models.ForeignKey(help_text='Company to which the items are being sold', limit_choices_to={'is_customer': True}, null=True, on_delete=models.SET(order.models.get_deleted_company), related_name='sales_orders', to='company.company', verbose_name='Customer'),
+        ),
+    ]

InvenTree/order/models.py

@@ -92,6 +92,9 @@ def get_next_so_number():
     return reference
 
 
+def get_deleted_company():
+    return Company.objects.get_or_create(name='deleted', email='deleted',is_deleted=True)[0]
+
 class Order(ReferenceIndexingMixin):
     """ Abstract model for an order.
 
@@ -219,7 +222,7 @@ class PurchaseOrder(Order):
                                          help_text=_('Purchase order status'))
 
     supplier = models.ForeignKey(
-        Company, on_delete=models.CASCADE,
+        Company, on_delete=models.SET(get_deleted_company),
         limit_choices_to={
             'is_supplier': True,
         },
@@ -567,7 +570,7 @@ class SalesOrder(Order):
 
     customer = models.ForeignKey(
         Company,
-        on_delete=models.SET_NULL,
+        on_delete=models.SET(get_deleted_company),
         null=True,
         limit_choices_to={'is_customer': True},
         related_name='sales_orders',