Re: multiple databases - two questions

On 3/01/2017 12:32 PM, Fred Stluka wrote:
> Mike,
>
> Maybe you don't need a custom DB manager. Perhaps a simple
> DB router would suffice? It's a Django way to specify which DB
> to use based on which model is being used, whether it is being
> read/written, etc.

That's the approach I took. The essence of the problem: it ain't simple.
There are many and varied relationships and any transfer of *related
sets* of data to another database means transferring existing PKs which
tie the sets together. Maybe if it was a foreseen design criterion we
would have used UUIDs instead of incrementing integer ids.

The DB router is designed for naturally segmented schemas being on
different databases. My attempt was against the grain.

Cheers

Mike

>
> See:
> -
> https://docs.djangoproject.com/en/dev/topics/db/multi-db/#topics-db-multi-db-routing
>
> --Fred
> ------------------------------------------------------------------------
> Fred Stluka -- mailto:fred@bristle.com -- http://bristle.com/~fred/
> Bristle Software, Inc -- http://bristle.com -- Glad to be of service!
> Open Source: Without walls and fences, we need no Windows or Gates.
> ------------------------------------------------------------------------
>
> On 11/4/16 12:37 AM, Mike Dewhirst wrote:
>> (this one might be easier to read)
>>
>> I am planning some utility helper code to push selected records and
>> their children from our staging database into the production
>> database. The current database would be 'default' and I could add a
>> second one called 'production' then read from 'default' and write to
>> 'production'. (I need to check we are on the staging server).
>>
>> The docs say ...
>>
>> https://docs.djangoproject.com/en/1.8/topics/db/multi-db/#using-managers-with-multiple-databases
>>
>>
>> ... but I don't quite understand. There are no custom managers
>> involved; only the out-of-the-box MyModel.objects.
>>
>> Q1. Should I be using db_manager()?
>>
>> The plan is to write some utility code like this ...
>>
>> from substance.models import Substance
>>
>> def
>> write_substance_to_production(subst):
>>
>> prd_subst, create =
>> Substance.objects.using('production').get_or_create(
>>
>> name=subst.name,
>>
>> )
>>
>> if create:
>>
>> pass
>>
>> # copy all subst attributes except id to prd_subst
>>
>>
>> Q2. Is this a reasonable approach?
>>
>> Thanks for any hints
>>
>> Mike
>>
>
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