[Seaside] Transactions, database connections, indices, GOODS and Seaside

[Avi Bryant]

On May 13, 2004, at 5:24 PM, C. David Shaffer wrote:

> Thanks guys.  I'm using GOODS right now and each session registers the 
> active DB in a dynamic variable during request processing.

I'm not sure what your usage patterns are for GOODS, but unless you're 
opening a new connection for every request (which would be pretty 
inefficient), I don't see why this wants to be a dynamic variable - any 
given session should always use the same connection.  You might be able 
to share one connection between several sessions, with appropriate 
mutexing, but I definitely wouldn't want to switch connections halfway 
through a session, because the object identities would be all wrong.  
Or am I missing something?

>
>    ^SCCurrentTransaction
>        use: (1 to: 100) atRandom
>        during: [super responseForRequest: aRequest]
>
> but this code only results in a single value for SCCurrentTransaction 
> for each session.  Why is that?  It certainly doesn't fit with a view 
> of dynamic scope sans continuations.  Is this a subtly caused by 
> continuations or error handling that messes up the dynamic binding 
> mechanism?

It's a subtlety of continuations.  You will probably find that it isn't 
exactly one value per session, but rather per component or task - a 
#call: is likely to change the value.  This makes sense if you think 
about it - you have to be using the same stack for the duration of a 
task's #go method.  There's a new call to #responseForRequest: every 
time, of course, but then you jump back into the old stack.

It's an interesting point, though, and one I hadn't fully thought 
through until now.  I guess it means that the correct pattern for 
dynamic variables is to store them in the session, and then have 
something like:

SCCurrentTransaction class>>value
	^ WACurrentSession value currentTransaction

It may be worth making that a standard part of Session...

Cheers,
Avi