[Twisted-Python] twisted.enterprise / transactions

[Itamar Shtull-Trauring]

Bob Ippolito wrote:

> It seems that enterprise expects that you want to commit data for every 
> successful query?  This certainly makes things simpler, as with 
> PostgreSQL a separate backend (connection) is going to be running for 
> every connection to that database, which means the thread pool would 
> require some more complicated management.  There ought to be a way to 
> set it up such that your callbacks can do more processing and guarantee 
> that it happens in the same thread, so you get the same connection, and 
> don't have to commit every time.  Committing after every query kinda 
> defeats the purpose of having transactions at all, unless you do 
> everything in user defined functions (stored procedures) that use 
> transactions themselves.


There is support for doing so.


Specifically, adabpi.ConnectionPool.interaction() lets you pass a 
callable object  (a function or method). The method you pass will be 
called with an instance of adabpi.Transaction, upon which you can run a 
series of SQL commands, after which the changes will be commited 
automatically (or rollbacked if there's an exception thrown.)

So, write a function that accepts one argument, an instance of 
adbapi.Transaction, and does a series of SQL commands on this instance. 
Then, pass this function to your connectionpoool's interaction() method.


> One more thing, do you need to do anything with threadable before using 
> enterprise?

Nope, it will automatically do that for you, on the assumption 
enterprise.adbapi is imported before your program starts, i.e. before 
you call your Application's run() method (or t.i.main.run()).