Postgresql needs typecasting for turning char fields into native UUID fields.

Conditionally run the necesary SQL for this to happen. GitLab issue #266 Thanks to Baptiste GAULLET @bat79a for finding the solution.

mayan/apps/documents/migrations/0032_auto_20160315_0537.py

@@ -1,12 +1,12 @@
 # -*- coding: utf-8 -*-
 from __future__ import unicode_literals
 
-from django.db import migrations, models
 import uuid
 
+from django.db import connection, migrations, models
+
 
 class Migration(migrations.Migration):
-
     dependencies = [
         ('documents', '0031_convert_uuid'),
     ]
@@ -18,3 +18,13 @@ class Migration(migrations.Migration):
             field=models.UUIDField(default=uuid.uuid4, editable=False),
         ),
     ]
+
+    def __init__(self, *args, **kwargs):
+        super(Migration, self).__init__(*args, **kwargs)
+
+        if connection.vendor == 'postgresql':
+            self.operations.insert(
+                0, migrations.RunSQL(
+                    'ALTER TABLE documents_document ALTER COLUMN uuid SET DATA TYPE UUID USING uuid::uuid;'
+                )
+            )