On Dec 24, 2009, at 3:44 PM, Nick Retallack wrote:
> I've looked at sqlalchemy-migrate, but I can't figure out how it
> works. Can you give me an example of how to rename a column in an
> existing table?
Simple procedures like that are documented on the migrate site.
> They mention it here, but it's unclear where this column object came
> from. What if I created my tables using the declarative syntax, or
> elixir? Am I supposed to import the column I'm about to alter from my
> application somehow, and then call rename on the sqlalchemy object?
I just reflect the tables I need wihtin the migration script, using "mytable =
Table('mytable', metadata, autoload=True)" . It doesn't matter what system
was used to generate the existing schema.
> And how does this work? Does sqlalchemy-migrate monkey-patch the
> standard sqlalchemy column so that same object now has extra methods?
that is what they do, yeah.
> And what about how it advises me not to import things from my
> application? Perhaps the code for this table no longer exists when
> I'm running the migration, so I can't import that column anymore? Can
I think they are a little hysterical in their documentation regarding this.
Just reflect the tables you need, there's no need to repeat the existing
structure of tables in the migration scripts or worry about whatever the
related code says or does not say.
> I get sqlalchemy-migrate to just find a table in my database by name,
> instead?
that's reflection (see above). At some point someone needs to convince them
its OK to use reflection and to have them change their docs.
>
> It would be much simpler if I could just print out the new schema and
> change things manually.
this is described in the FAQ entry I sent in my previous email.
> In the IRC, people mentioned they just
> generate a new database in order to see what the new schema is, and
> then destroy it. This seems pretty silly to me.
I've no idea what that practice is.
>
> On Dec 22, 2:06 pm, Michael Bayer <mike...@zzzcomputing.com> wrote:
>> On Dec 21, 2009, at 9:05 PM, Nick Retallack wrote:
>>
>>> Say you've created some models in SQLAlchemy, and run create_all() to
>>> get them into the database. Later on, you changed some of their
>>> definitions, and you need to update the database schema to correspond
>>> to it. How would you do this? Can you get SQLAlchemy to output the
>>> current SQL representation of your models?
>>
>> since nobody has gotten to this today, this is in the FAQ
>> athttp://www.sqlalchemy.org/trac/wiki/FAQ#HowcanIgettheCREATETABLEDROPT....
>> You also should look at sqlalchemy-migrate
>> athttp://code.google.com/p/sqlalchemy-migrate/.
>>
>>
>>
>>
>>
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