On Jul 10, 2010, at 1:08 AM, Steven Wei wrote:
> On Jun 17, 4:00 am, Francisco Souza <franci...@franciscosouza.net>
> wrote:
>>> But do I do this? Part of the problem is that I don't know of a way
>>> to generate tables other than create_all() (or drop_all()) when using
>>> declarative syntax. Is there another way?
>>
>> Hi Shane :)
>>
>> When you bind your declarative base to a metadata, the "metadata" object has
>> a attribute called "tables", wich is a dict with all tables containeds in
>> this metadata. So, you can do a create for a single table easily.
>>
>>>>> Base.metadata.tables['test_case'].create(engine)
>>
>> You can call it on your upgrade function inside the migration module.
>
> Isn't this incredibly problematic if you need to change the model
> definition later? What if you need to add a column to this table in a
> new migration later on?
>
> It will work on your existing databases, but if you run through your
> migrations on a fresh database, you'll have a problem because the
> first migration created the table with the extra column in place, and
> the second migration won't be able to add the column again.
>
> The sqlalchemy-migrate docs suggest you copy and paste Table
> definitions to avoid this behavior (ugh). But when you're using
> DeclarativeBase you don't even have any Table definitions to copy
> from!
the sqlalchemy-migrate docs are insane in this regard. Use reflected tables
in your migrations scripts, that way you don't have to worry at all about what
the status of the table is other than the thing you are migrating. When I
eventually get around to releasing Alembic, you won't even have to reflect
anything, you can just specify the alterations you care about.
>
> Is there any way around this other than not running migrations when
> creating new databases (and instead sticking with create_all()
> directly)?
i havent read the thread here, but if the issue is, how to create new databases
when you're up to version 67 in your migrations, issue the create_all(), then
create the migration table, then set the version to the most recent. Code
looks like this:
from migrate.versioning.api import version_control, version, upgrade
from migrate.versioning.exceptions import DatabaseAlreadyControlledError
Base.metadata.create_all(bind=engine, checkfirst=True)
# setup migrate versioning table if not present
try:
latest_version = version("migrate")
version_control(url, "migrate", version=latest_version, echo=True)
except DatabaseAlreadyControlledError:
log.info("migrate table already present")
# do any migrate upgrades pending...
upgrade(url, "migrate", version=latest_version, echo=True)
my apologies if this is not the question being asked.
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