Hi Babu,

This can be implemented as follows. In old api,

def _get_default_address(self, cr, uid, ids, field_name, arg, context=None):
    res = {}
    partner_obj = self.pool.get('res.partner')
    for data in self.browse(cr, uid, ids, context=context):
        adr_id = False
        if data.partner_id:
            adr_id = partner_obj.address_get(cr, uid, [data.partner_id.id], ['contact'])['contact']
        res[data.id] = adr_id
    return res
_columns ={
        'default_address_id': fields.function(_get_default_address, type="many2one", relation="res.partner"),
}

 In new api, it will be as follows:

default_address_id = fields.Many2one(compute="_get_default_address", relation="res.partner")