Re: Context manager to pick which database to use?

[Peter Coles]

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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Re: Context manager to pick which database to use?

[Simon Charette]

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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Re: Context manager to pick which database to use?

[Peter Coles]

Or maybe more versatile would be a context manager that accepts a database 
router. Something like the following?

with database_router(my_router):
   …



On Tuesday, April 28, 2015 at 3:26:48 PM UTC-4, Peter Coles wrote:
>
> 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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