#--------------- Class 2----------------

class class2(models.Model):

_name = 'class2'

_description = 'Class 2'

item_order_line = fields.Many2one('class1','Item')

item_id = fields.Char('Item Number')

item_title = fields.Char('Item Title')

quantity_ordered = fields.Integer('Quantity')

sale_price = fields.Char('Sale Price')

#----------------- Class 1 -----------------

class class1(models.Model):

_name = 'class1'

_description = 'Class 1'

_inherit = ['class2']

#------------------ o2m -----------------

order_line = fields.One2many('class2','item_order_line',string='Order Lines')

Example ;)