[6.1] Fetchmail + file storage + duplicate attachment = uniqueness constraint violation

[Stefan Rijnhart (Opener)]

On a system with document storage enabled, fetchmail will try to create a mail with attachment_ids set to [(6, 0, [1234, 1234])] if an email contains the same document twice. This leads to the following error:

  File "/home/openerp/openobject-addons/mail/mail_thread.py", line 134, in message_new
    self.message_append_dict(cr, uid, [res_id], msg_dict, context=context)
  File "/home/openerp/openobject-addons/mail/mail_thread.py", line 305, in message_append_dict
    context = context)
  File "/home/openerp/openobject-addons/mail/mail_thread.py", line 269, in message_append
    mail_message.create(cr, uid, data, context=context)
  File "/home/openerp/openobject-addons/fetchmail/fetchmail.py", line 250, in create
    res = super(mail_message,self).create(cr, uid, values, context=context)
  File "/home/therp/bzr/openobject-server/openerp/osv/orm.py", line 4235, in create
    result += self._columns[field].set(cr, self, id_new, field, vals[field], user, rel_context) or []
  File "/home/therp/bzr/openobject-server/openerp/osv/fields.py", line 784, in set
    cr.execute('insert into '+rel+' ('+id1+','+id2+') values (%s, %s)', (id, act_nbr))
  File "/home/therp/bzr/openobject-server/openerp/sql_db.py", line 152, in wrapper
    return f(self, *args, **kwargs)
  File "/home/therp/bzr/openobject-server/openerp/sql_db.py", line 212, in execute
    res = self._obj.execute(query, params)
IntegrityError: duplicate key value violates unique constraint "message_attachment_rel_message_id_key"