On Sun, Apr 29, 2012 at 11:13 PM, Michael Bayer
<mike...@zzzcomputing.com> wrote:
>
> On Apr 29, 2012, at 10:56 AM, limodou wrote:
>
>> On Sun, Apr 29, 2012 at 10:42 PM, Michael Bayer
>> <mike...@zzzcomputing.com> wrote:
>>> You would assemble a multi-database scheme of your choosing in env.py. If
>>> you do "alembic init multidb" you'll see an example of one. How env.py
>>> is organized depends greatly on the relationship of the databases to each
>>> other, that is, to what degree they are mirrors of each other versus
>>> storing different schemas.
>>>
>>
>> If I ran the command:
>>
>> alembic init multidb
>>
>> It'll create multidb folder and copy files in it. But I saw the
>> alembic.ini will be the same one. So if I should change it myself? And
>> how to let alembic know different database when executing commands
>> like: revision, upgrade, etc. It seems that no database parameter
>> existed.
>>
>> And if I can manage different databases in one directory or in one ini file?
>
> multidb has a different alembic.ini as an example. If you already had an
> alembic.ini there it wouldn't overwrite it.
>
> if you really wanted two completely independent sets of migration scripts,
> then you'd run two migration environments.
>
> They can share the same alembic.ini like this:
>
> [my_db_one]
> sqlalchemy.url =
>
> [my_db_two]
> sqlalchemy.url =
>
> you then run alembic with "alembic -n my_db_one" or "alembic -n my_db_two".
> The "default" config area is set by -n.
>
> A single env.py script can get multiple database URLs in any way it wants, as
> it determines how config is accessed. If you look in the multidb/env.py
> script, you'll see it's pulling multiple database urls from one section using
> config.get_section(name) - config file:
>
> [alembic]
> # path to migration scripts
> script_location = ${script_location}
>
> # template used to generate migration files
> # file_template = %%(rev)s_%%(slug)s
>
> databases = engine1, engine2
>
> [engine1]
> sqlalchemy.url = driver://user:pass@localhost/dbname
>
> [engine2]
> sqlalchemy.url = driver://user:pass@localhost/dbname2
>
> usage:
>
> config = context.config
>
> db_names = config.get_main_option('databases')
>
> for name in re.split(r',\s*', db_names):
> engines[name] = rec = {}
> rec['engine'] = engine_from_config(
> config.get_section(name),
> prefix='sqlalchemy.',
> poolclass=pool.NullPool)
>
> Over here I have both forms of multi db at the same time. There's two
> migration environments, and one migration environment does two databases that
> are largely mirrored, so three databases total. All three make use of a
> common env.py script that's in my application as a library, they then
> implement an env.py in the migration environment that draws upon the
> myapp/lib/env.py script for common features.
>
> You can pass instructions to a single env.py that may be controlling multiple
> databases using --tag:
>
> "alembic --tag my_tag"
>
> "my_tag" is available in env.py as context.get_tag_argument(). You can use
> that to conditionally run migrations on one database or the other.
>
> This is all DIY. Multi-database migrations can happen in many different ways
> so you'd need to build the approach that suits your situation best.
>
>
thank you very much.
--
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