Question about programmatically fetching the current state of migrations

[Jannis Leidel]

Hi all,

I'm looking for a way to programmatically figure out if all migrations have been applied without actually running the migrations, basically a programmatic way to get the "Target database is not up to date" response.

Has anyone worked on that before and cares to share their solutions?

Best,

Jannis

[Felix Schwarz]

Maybe something like this?
https://github.com/mediadrop/mediadrop/blob/master/mediadrop/migrations/util.py
(IIRC it works with an older version of alembic but I think most of the code
still works with the latest version.)

Felix

[Mike Bayer]

well, the "alembic current" command gives you the current status of
the revisions in the database, and the "alembic heads" command shows
you the current "head" versions represented in the versions/
directory. These used to both be just a single value, but now that
Alembic supports branches they can be lists of values.

if you look in http://alembic.zzzcomputing.com/en/latest/api/runtime.html?highlight=migrationcontext#alembic.runtime.migration.MigrationContext,
there's an example of how to get the database version:

# in any application, outside of an env.py script
from alembic.migration import MigrationContext
from sqlalchemy import create_engine

engine = create_engine("postgresql://mydatabase")
conn = engine.connect()

context = MigrationContext.configure(conn)
current_rev = context.get_current_revision()

similarly, the ScriptDirectory can get you those "heads" from your
versions/ directory, and the docstring at
http://alembic.zzzcomputing.com/en/latest/api/script.html?highlight=scriptdirectory#alembic.script.ScriptDirectory
also illustrates this:

from alembic.script import ScriptDirectory
from alembic.config import Config
config = Config()
config.set_main_option("script_location", "myapp:migrations")
script = ScriptDirectory.from_config(config)

head_revision = script.get_current_head()


the above two examples illustrate the "single head" version. For
branch support, you'd use context.get_current_heads() and
script.get_heads(). the docstrings for those methods should link to
all of this.










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> Jannis
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