Set on_delete action to SET_NULL on Document.uploaded_by_user

This prevents deletion of users from deleting any Documents they have uploaded.

This is already the behaviour on images.

CHANGELOG.txt

@@ -17,6 +17,7 @@ Changelog
  * Fix: Fixed typo in Wistia oEmbed pattern (Josh Hurd)
  * Fix: Added more accurate help text for the Administrator flag on user accounts (Matt Fozard)
  * Fix: Tags added on the multiple image uploader are now saved correctly
+ * Fix: Documents created by a user are no longer deleted when the user is deleted
 
 1.3.1 (05.01.2016)
 ~~~~~~~~~~~~~~~~~~

docs/releases/1.4.rst

@@ -36,6 +36,7 @@ Bug fixes
  * Fixed typo in Wistia oEmbed pattern (Josh Hurd)
  * Added more accurate help text for the Administrator flag on user accounts (Matt Fozard)
  * Tags added on the multiple image uploader are now saved correctly
+ * Documents created by a user are no longer deleted when the user is deleted
 
 
 Upgrade considerations

wagtail/wagtaildocs/migrations/0005_alter_uploaded_by_user_on_delete_action.py

@@ -0,0 +1,22 @@
+# -*- coding: utf-8 -*-
+# Generated by Django 1.9 on 2015-12-22 16:09
+from __future__ import unicode_literals
+
+from django.conf import settings
+from django.db import migrations, models
+import django.db.models.deletion
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('wagtaildocs', '0004_capitalizeverbose'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='document',
+            name='uploaded_by_user',
+            field=models.ForeignKey(blank=True, editable=False, null=True, on_delete=django.db.models.deletion.SET_NULL, to=settings.AUTH_USER_MODEL, verbose_name='uploaded by user'),
+        ),
+    ]

wagtail/wagtaildocs/models.py

@@ -34,7 +34,8 @@ class AbstractDocument(models.Model, TagSearchable):
         verbose_name=_('uploaded by user'),
         null=True,
         blank=True,
-        editable=False
+        editable=False,
+        on_delete=models.SET_NULL
     )
 
     tags = TaggableManager(help_text=None, blank=True, verbose_name=_('tags'))