How does using HTTP preclude that?
So if I had insert and delete permissions on the Hacker News comments table to insert or delete my own posts, I could insert and delete every user's posts.
It's possible to imagine hacks that might work around this problem (e.g. comments-table-per-user, or liberal use of stored procedures) but none of them sound like particularly good ideas.
Actually, many RDBMSs (postgres included) provide security at the command, relation (table/view), and column level.
With that, and appropriate view definitions and triggers, you can essentially as fine-grained permissions as you'd like. We manage this all client side because while much of the theory of this has been around for servers and held up as the ideal model since very early in the RDBMS era, a lot of the necessary features were not implemented in many servers (or implemented so wildly inconsistently between servers as to make practical, rather than theoretical, knowledge sharing in the community difficult.) That's less true now, though it still requires implementation-specific knowledge for the SQL implementation you are using.
but this could be a moot point as long as db communication is only done server-side so it can be behind company firewall anyway -- after all, isn't that why the current db security model works? No one should EVER post ajax to the db, essentially. & i dont think anyone is suggesting that, i hope
As far as business logic, how is an RDBMS going to make sure that your remaining balance on your gift card is higher than that order you just put in? Sure, you can validate that on the client side, but I can just as easily use anything that will make an http request to make that same http request without doing any business rules validation. Heck, I can alter javascript while it's running just to circumvent business logic if I so desire.
per command and per relation is more common (though many databases, including Postgres, actually also include column-level permissions, as well), but relations aren't restricted to base tables.
> true app security often needs to be per-row, or even per-column, perhaps depending on data in the other columns of the same row.
The effects of per column and per row security can (even if per-column permissions aren't directly available), in most DB engines, be managed using either views, stored procs, or both.
> As far as business logic, how is an RDBMS going to make sure that your remaining balance on your gift card is higher than that order you just put in?
A few options:
(1) Order submission is a call to a stored proc which performs the validation then does any necessary table updates, or
(2) Order submission is through insert to a table (or view) which has an appropriate BEFORE INSERT trigger that performs the validation,
(3) Order submission is an uncondition insert to a table, but that table is just an "incoming_orders" table that isn't particularly actionable -- the actionable views on that table (executable_orders and orders_with_payment_errors, say) are views that based on joins that validate the payment information, including gift cards.
There's probably other database-side ways of dealing with that problem, as well.
The same way you already do?
>Database security is at best per-command and per-table, when true app security often needs to be per-row, or even per-column, perhaps depending on data in the other columns of the same row.
Stored procedures already solve all the problems you are imagining. Sane people already use them anyways.
>As far as business logic, how is an RDBMS going to make sure that your remaining balance on your gift card is higher than that order you just put in?
The same way it already does? If your database is not enforcing those rules then you are already doing it very wrong.
How does using HTTP preclude that?
>Additionally, you should always validate business logic on the back end.
Uh huh? So how is talking to the back end going to prevent that?