Re: Unintuitive behaviour of management commands with multiple databases

Dear Carl,

On Tuesday, February 2, 2016 at 7:51:20 PM UTC, Carl Meyer wrote:

There's nothing wrong with connections[options.get('database')] if you
want to get a specific database connection object; that's public API and
you can use it. In the case of the built-in commands, that's useful

OK, perhaps I misunderstood what you said in an earlier comment - I see you were talking against using the internals of the connection rather the connection itself.

because they need to do low-level things with the connection; I don't
think it helps you for regular ORM use. It doesn't allow changing the
default connection for ORM usage. Where the built-in management commands
do use the higher-level ORM, they use the public `using` APIs.

 

That's fine for simple use, but it's not good have lots of using() calls for models when it's not a "real" multi-DB scenario,

 

If you want to write a management command that has a --database option
like the built-in ones and makes heavy use of the ORM, you can a)
explicitly provide `using` where needed , b) use
django-dynamic-db-router, or c) hold your nose and monkeypatch
DEFAULT_DB_ALIAS, since it's just a one-shot management command and you
don't need to be as concerned about cleaning up after yourself.

Personally I would go for (a) or (b), depending on just how much I was
using the ORM in the management command. I'm not convinced that a fourth
(or third supported public) option is necessary here. If it's just a few
queries, you use `using`, if it's more than that and you want a broader
policy applied, you use a database router.

 

OK, thanks for the suggestion - you've been very helpful, as always. I'll mull things over and see what's the best for the specifics of the specific project.

Regards,

Vinay Sajip

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