I have an object that, when it completes it's workflow, needs to update the state for a different class, specifically manufacturing orders. I have tried everything I can think of to try to update that field. Code is thus:

class mrp_partsorder(osv.Model):
    ...

    _columns = {
    'sourceorder_id': fields.many2one('mrp.production', string='Manufacturing Order'
    'primarystate': fields.selection ( [..states...], related='sourceorder_id.state'
    }

    def partsorder_complete(self, cr, uid, ids, context=None):
        prod_obj = self.pool.get('mrp.production')
        prod_ids = [self.sourceorder_id]
        prods = prod_obj.search(cr, uid, prod_ids, context=context)
        proc_obj.action_fitting(cr, uid, prods, context=context)
        res = self.write(cr, uid, ids, {'state': 'complete'}, context=context)

class mrp_production(osv.osv)
    def action_fitting(self, cr, uid, ids, context=None):
        res = self.write(cr, uid, ids, {'state': 'fitting'}, context=context)
        return res 
     

At the moment I'm getting the following error:

ValueError: "'mrp.partsorder' object has no attribute '_ids'" while evaluating
u'partsorder_complete() 

This is not the only error I've seen, as I've tried quite a few different ideas of solving this problem. Basically, i just want to update the value in the related field (primarystate), but if I write to that field it updates the mrp.partsorder table but not the mrp.production table. So, I figured I needed to use self.pool.get to get the singleton instance of mrp.production and then use the the write method for mrp.production or use the action_fitting() method for mrp.production. 

What is the best way to solve this problem?

Edit: After further consideration I realized that I need to use the function on mrp.production to change the state, rather than just writing to it. I want to do this because of all the functionality built into the manufacturing order. All I need now is to figure out how to call the function from my mrp.partsorder.partsorder_complete() function.