Catch re-launching a workflow for a document and logging the condition

mayan/apps/document_states/models.py

@@ -1,8 +1,10 @@
 from __future__ import unicode_literals
 
+import logging
+
 from django.contrib.auth.models import User
 from django.core.urlresolvers import reverse
-from django.db import models
+from django.db import IntegrityError, models
 from django.utils.encoding import python_2_unicode_compatible
 from django.utils.translation import ugettext_lazy as _
 
@@ -10,6 +12,8 @@ from documents.models import Document, DocumentType
 
 from .managers import WorkflowManager
 
+logger = logging.getLogger(__name__)
+
 
 @python_2_unicode_compatible
 class Workflow(models.Model):
@@ -31,7 +35,13 @@ class Workflow(models.Model):
             return None
 
     def launch_for(self, document):
+        try:
+            logger.info('Launching workflow %s for document %s', self, document)
             self.instances.create(document=document)
+        except IntegrityError:
+            logger.info('Workflow %s already launched for document %s', self, document)
+        else:
+            logger.info('Workflow %s launched for document %s', self, document)
 
     class Meta:
         verbose_name = _('Workflow')