Getting this error: AttributeError: 'int' object has no attribute 'get'

with the following code: class account_invoice_refund(osv.osv):

_inherit = 'account.invoice.refund'

   def MES_Refund_Button(self,cr,uid,ids,context):
             transaction_id = str( self.pool.get('account.invoice').read(cr,uid,ids,['mes_code'],context['active_id'])[0]['mes_code'] )

I extended the account_invoice object with those columns already, but pushing that button from the wizard doesn't get the data field from the account_invoice object

I guess the broader question asked here is: How do I properly get information from a view that isn't the current one?