Are Joins possible with VPD predicates?

Question

Hi everybody,
I have read the articles about VPD and row level security. What occurs to me is that all examples return predicates where the WHERE clause selects from the same table as the FROM clause. Is there a way to generate a predicate that goes to other tables as well?
Example:
table_1 holds sales records information, e.g.:
product, price, date of sale transaction.
table_2 holds information about the customers, e.g.:
customer_company, product, price, date_of_sale_transaction.
table_3 holds information about the customer account managers, e.g.:
employee_id, family_name, name, customer_company, customer_department.
Now if an account manager logs in to the database he shall only see the sold products in table_1 which were bought by the customers who he is in charge of. The select statement would something like:
select t1.product, t1.price from table_1 t1, table_2 t2, table_3 t3 where t1.product=t2.product and t2.customer_company=t3.customer_company and t3.employee_id=?
Certainly, ? would be the the id of the logged in user.
How can I realize a JOIN like this with VPD?
Thank you for every help!
Jie

Answer 1

Jie,
This is trivial to do in VPD. In your case, you would define a different policy on each table. For instance, the policy function for the policy on table_3 will return a preciate
employee_id = USER
or something similar. The policy function for policy on table_2 will return
customer_company in (select customer_company from table_1)
Similarly, the function for table_1 will return
product_in (select product from table_2)
However, you will note that the query containing IN quickly becomes inefficient when the data volume is high. Therefore, an alternative solution may be in order. One option is to use application contexts where you prepopulate the values when the user logs in and use that in the predicate. It's not possible to describe the whole procedure here; but youmay find the paper I presented at New York Oracle User Group helpful at my website www.proligence.com/nyoug_fgac.pdf.
Hope this helps.
Arup Nanda