Pan Luo <luopa...@gmail.com> wrote:
> Thanks Michael for the tip. Here is the code I came up. Please feel free to
> make changes and use in your cookbook:
>
>
> Use Case 1: If someone new come to the project and they use db.create_all()
> or some script to create a fresh new database. There is no alembic_version
> table and the person will run into problems when doing the upgrade. The
> following code snippet can be added to database (re)create script to make
> sure the new database has most up-to-date version.
> # create db tables
> db.create_all()
> # add database version table and add current head version
> alembic_cfg = Config("alembic.ini")
> connection = db.engine.connect()
> context = MigrationContext.configure(connection)
> context._ensure_version_table()
> script = ScriptDirectory.from_config(alembic_cfg)
> head_revision = script.get_current_head()
> context.stamp(script, head_revision)
you shouldn’t be calling _ensure_version_table(). You should be calling
command.stamp() which will run the full migration environment and ensure the
version table is present. The recipe at
http://alembic.readthedocs.org/en/latest/cookbook.html#building-an-up-to-date-database-from-scratch
should be doing what this is trying to do, and if it doesn’t work right now,
that’s a bug. Additionally, there is no need for “get_current_head()”,
command.stamp() can be called with the string “head” directly.
> Use Case 2: When doing tests, you may want to test your database migration
> script as well. Here is the code snippet:
> # in your tests
> def test_migration(self):
> # create database
> db.create_all()
> # create config object
> alembic_cfg = Config("alembic.ini")
> # get connection from db object
> connection = db.engine.connect()
> alembic_cfg.connection = connection
> # make sure version table exists or create one
> context = MigrationContext.configure(connection)
> context._ensure_version_table()
> # insert/update the head version
> script = ScriptDirectory.from_config(alembic_cfg)
> head_revision = script.get_current_head()
> context.stamp(script, head_revision)
same here. the only difference here is that you want to send through a SQLite
:memory: database, so you can attach that to alembic_cfg and have it invoked
inside of your env.py as the source of connectivity.
>
> command.downgrade(alembic_cfg, "base")
>
> command.upgrade(alembic_cfg, "head")
>
> # in your alembic/env.py
> def run_migrations_online():
> """Run migrations in 'online' mode.
>
> In this scenario we need to create an Engine
> and associate a connection with the context.
>
> """
> # the connection may come from the config object
> if hasattr(config, 'connection'):
> # load connection from config object
> connection = config.connection
> else:
> # load connection from config file
> engine = engine_from_config(
> config.get_section(config.config_ini_section),
> prefix='sqlalchemy.',
> poolclass=pool.NullPool
> )
> connection = engine.connect()
>
> context.configure(
> connection=connection,
> target_metadata=target_metadata
> )
>
> try:
> with context.begin_transaction():
> context.run_migrations()
> finally:
> # don't close connection if it is from outside
> if not hasattr(config, 'connection'):
> connection.close()
>
>
> Hope it helps.
>
>
> Cheers,
> Pan
>
> On Fri, Dec 26, 2014 at 6:21 PM, Michael Bayer <mike...@zzzcomputing.com
> <mailto:mike...@zzzcomputing.com>> wrote:
> just tack it on the Config object for now, I’ll have to add more support for
> this kind of feature.
>
>
>
> Pan Luo <luopa...@gmail.com <mailto:luopa...@gmail.com>> wrote:
>
>> Looks like alembic_cfg only accepts string options. (set_main_option()). Is
>> there a way to pass connect object? Thanks.
>>
>>
>> Cheers,
>> Pan
>>
>> On Wed, Dec 24, 2014 at 8:35 AM, Michael Bayer <mike...@zzzcomputing.com
>> <mailto:mike...@zzzcomputing.com>> wrote:
>> Pan Luo <luopa...@gmail.com <mailto:luopa...@gmail.com>> wrote:
>>
>>> If someone new come to the project and they use db.create_all() or some
>>> script to create a fresh new database with declared models. There is no
>>> alembic_version table and he/she will run into problems when doing the
>>> upgrade. Is there something in alembic to support it? I have been poking
>>> around and came up with the following:
>>>
>>> alembic_cfg = Config("alembic.ini")
>>> context = MigrationContext.configure(db.engine.connect())
>>> current_rev = context.get_current_revision()
>>> context._ensure_version_table()
>>>
>>> script = ScriptDirectory.from_config(alembic_cfg)
>>> head_revision = script.get_current_head()
>>> context.stamp(script, head_revision)
>>>
>>> command.downgrade(alembic_cfg, "base")
>>>
>>> However, it works with file based sqlite db but no in memory one: Error:
>>> Destination base is not a valid downgrade target from current head(s)
>>>
>>> It seems the migrationcontext use different from the one I generated and
>>> the one used in the alembic, so the current revision was empty when I do
>>> the downgrade (just for. Not sure why file based sqlite works.
>>
>> A SQLite :memory: database only exists with the span of a single SQLite
>> database connection. You get that above when you call db.engine.connect().
>> But then when you call command.downgrade(), you are not passing this
>> connection to that command in any way; the connection is stuck inside your
>> MigrationContext which isn’t present in command.downgrade(alembic_cfg).
>> command.downgrade() then calls upon your env.py in order to get the database
>> connection, and you probably have another engine.connect() in there using a
>> different engine (and therefore connection pool). This makes a brand new
>> :memory: connection that has no state on it.
>>
>> So you’d want to send an argument into the alembic_cfg in this case which
>> refers to that connection from db.engine.connect(), which your env.py can
>> pull out and make use of instead of connecting in some other way. This
>> requires modifications to your env.py to look for this connection and use
>> it, instead of connecting again. Or you can set up this connection as a
>> global variable somewhere.
>>
>> This is a common issue so at some point I will add recipes to the
>> documentation that show how to transfer a connection from the outside of
>> command.xyz(), through the env.py and into the migration context.
>>
>>
>>
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