Disable select_for_update when checking the uniqueness of a

cabinet if the database backend is Oracle.
GitHub issue #258. Thanks to @simeon-walker for the report.

Signed-off-by: Roberto Rosario <roberto.rosario.gonzalez@gmail.com>

HISTORY.rst

@@ -7,6 +7,7 @@
 - Fix document page widget appearance in the document page list view.
 - Make document version order deterministic.
 - Allow total page number instrospection of encrypted PDF with non ASCII user properties. GitLab issue #411.
+- Oracle database compatibility update in the cabinets app. GitHub #258.
 
 2.6.1 (2017-07-18)
 ==================

mayan/apps/cabinets/models.py

@@ -1,7 +1,7 @@
 from __future__ import absolute_import, unicode_literals
 
 from django.core.exceptions import NON_FIELD_ERRORS, ValidationError
-from django.db import models, transaction
+from django.db import connection, models, transaction
 from django.urls import reverse
 from django.utils.encoding import python_2_unicode_compatible
 from django.utils.translation import ugettext_lazy as _
@@ -64,7 +64,12 @@ class Cabinet(MPTTModel):
         # https://code.djangoproject.com/ticket/1751
 
         with transaction.atomic():
-            if Cabinet.objects.select_for_update().filter(parent=self.parent, label=self.label).exists():
+            if connection.vendor == 'oracle':
+                queryset = Cabinet.objects.filter(parent=self.parent, label=self.label)
+            else:
+                queryset = Cabinet.objects.select_for_update().filter(parent=self.parent, label=self.label)
+
+            if queryset.exists():
                 params = {
                     'model_name': _('Cabinet'),
                     'field_labels': _('Parent and Label')

mayan/apps/cabinets/serializers.py

@@ -1,6 +1,6 @@
 from __future__ import unicode_literals
 
-from django.db import transaction
+from django.db import connection, transaction
 from django.utils.translation import ugettext_lazy as _
 
 from rest_framework import serializers
@@ -129,7 +129,12 @@ class WritableCabinetSerializer(serializers.ModelSerializer):
         # when there is a FK in the unique_together tuple
         # https://code.djangoproject.com/ticket/1751
         with transaction.atomic():
-            if Cabinet.objects.select_for_update().filter(parent=data['parent'], label=data['label']).exists():
+            if connection.vendor == 'oracle':
+                queryset = Cabinet.objects.filter(parent=data['parent'], label=data['label'])
+            else:
+                queryset = Cabinet.objects.select_for_update().filter(parent=data['parent'], label=data['label'])
+
+            if queryset.exists():
                 params = {
                     'model_name': _('Cabinet'),
                     'field_labels': _('Parent and Label')