Fix backup restore

This merge request fixes the backup restore system.

Note that it might not be backward compatible.

Fixes #492

beat/web/databases/models.py

@@ -301,6 +301,7 @@ class DatabaseProtocol(models.Model):
 
     def natural_key(self):
         return self.database.natural_key() + (self.name,)
+    natural_key.dependencies = ['databases.database']
 
     def fullname(self):
         if self.name != '':
@@ -394,6 +395,8 @@ class DatabaseSet(models.Model):
 
     def natural_key(self):
         return self.protocol.natural_key() + (self.name,) + self.template.natural_key()
+    natural_key.dependencies = ['databases.databaseprotocol',
+                                'databases.databasesettemplate']
 
     def fullname(self):
         if self.name != '':
@@ -472,3 +475,5 @@ class DatabaseSetOutput(models.Model):
 
     def natural_key(self):
         return (self.set.natural_key(), self.template.name)
+    natural_key.dependencies = ['databases.databasesettemplateoutput',
+                                'databases.databaseset']