Add "upload date" field to fileattachment base class

InvenTree/order/migrations/0034_auto_20200512_1054.py

@@ -0,0 +1,23 @@
+# Generated by Django 3.0.5 on 2020-05-12 10:54
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('order', '0033_auto_20200512_1033'),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name='purchaseorderattachment',
+            name='upload_date',
+            field=models.DateField(auto_now_add=True, null=True),
+        ),
+        migrations.AddField(
+            model_name='salesorderattachment',
+            name='upload_date',
+            field=models.DateField(auto_now_add=True, null=True),
+        ),
+    ]