Tuesday, April 28, 2015

Re: Context manager to pick which database to use?

Thanks for the reply Simon. Yeah, I'm using `using` for now, just thought it'd be nice to somehow wrap the logic, especially if it could magically pass through to underlying function calls. I am experimenting with having a `readonly` manager that just adds a `.using('readonly')`, dunno how ~djangonic~ that is.

Cheers,
Peter

On Tuesday, April 28, 2015 at 3:58:15 PM UTC-4, Simon Charette wrote:
Hi Peter,

I think you could use database routers to declare the default behavior and rely on the using() queryset method for the exceptional case?

I'm afraid the introduction of a context manager would require the addition of a thread-local global state that a database router could rely on.

Simon

Le mardi 28 avril 2015 15:26:48 UTC-4, Peter Coles a écrit :
When using multiple databases, I would love for a simple way to declare which database should be used during execution of django ORM calls. Perhaps this could even use a context manager and look something like this:

# declare that all calls within this context should default to using 'readonly' db instead of 'default'
with database('readonly'):
    things
= models.MyThing.objects.all()


   
# inside this function call the 'readonly' db would be used too (unless overridden by `.using(...)`)
    more_things
= some_lib.some_function(things)

In my app I have a write database and a read-only replica. The read-only replica might have a delay, so I don't want to use it in normal live requests, but I would like certain dashboards to use it. For this reason I assume that the database router approach doesn't properly apply?

Does something like this exist? If not, any thoughts on if it might be useful and where I might consider poking around in the ORM?

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