Hi
This seems like a genuine bug, Django should not assume that all backends
have the same max table name length. Please file a ticket.
You can workaround this right now by defining db_table on your model. You
might need two model classes, sharing details via inheritance, for the
different backends though.
I can see two solutions, either:
- truncate to the minimum max length across all models
- remove the truncation behaviour and instead have a system check error
triggered when a table name is too long for at least one backend. This
would allow users to be explicit about the fix, would not change table
names when adding/changing database backends, and would remove the somewhat
undesirable/confusing hash at the end of table names.
Either looks like they'd need to go through the deprecation pathway.
Thanks,
Adam
On Wed, 14 Apr 2021 at 11:53, Javier Buzzi <buzzi.jav...@gmail.com> wrote:
> I have a model with a really long name think
> `ThisIsAReallyLongModelNameThatIsAlsoVeryOld`. To complicate things further
> I have a Oracle instance without archival data designated connection name
> `old` and a new postgres instance with the connection name `default`.
>
> Issue i've found is that if i try and call the model
> `ThisIsAReallyLongModelNameThatIsAlsoVeryOld.objects.using('old').count()`
> i get an error saying that the table `APP_THISISAREALLYLONGMODEL5300` does
> not exist, when it should be using `APP_THISISAREALLYLONGMODEL5BD6`
> instead. By the way when I use postgres, it works as expected:
> `ThisIsAReallyLongModelNameThatIsAlsoVeryOld.objects.using('default').count()`
>
> This is because the default connection is used when the model is
> instantiated, and then its used from that moment on.
>
>
> https://github.com/django/django/blob/stable/3.2.x/django/db/models/options.py#L207
>
> This is an issue that seems to go back to the beginning of Django.
>
> Is this something known? Is this something we can fix?
>
> Thanks,
>
>
> ================= here be dragons ===================
> as a temporary hack i did this for now, sorry for the formatting, google
> groups didn't let me format it the way i wanted.
>
>
> from django.db.models.sql import compiler
> from django.db.backends.utils import truncate_name
>
>
> class ConnectionAwareAlias(dict):
> def __init__(self, query, connection):
> self.query = query
> self.connection = connection
> self['*'] = '*'
>
> def __contains__(self, item):
> model = self.query.model
> db_table = "%s_%s" % (model._meta.app_label, model._meta.model_name)
> if item == db_table:
> if not self.get(item):
> db_table = truncate_name(db_table, self.connection.ops.max_name_length())
> self[item] = db_table
>
> return True
>
> return self.get(item) is not None
>
>
> class NewSQLCompiler(compiler.SQLCompiler):
> def __init__(self, query, connection, using):
> super(NewSQLCompiler, self).__init__(query, connection, using)
> self.quote_cache = ConnectionAwareAlias(query, connection)
>
> compiler.SQLCompiler = NewSQLCompiler
>
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