just so you know, surgical-precision downgrades will be more reliable once we get the 1.6 series of Alembic out, where we have a total rewrite of how the internal traversal works in order to make upgrade/downgrades across complex trees more reliable. downgrades are not *too* common in production systems.
On Tue, Mar 9, 2021, at 10:15 PM, 'br...@derocher.org' via sqlalchemy-alembic wrote: > c787 did not fail, nor did 60e8 on upgrade. According to alembic history, > alembic ran 1efb before c787. So the result is I have a view in my database > that will never get used because the query is now embedded in code. The > solution is clear. 60e8 should drop a view if there is one. > > For downgrade we get lucky. > > I feel the situation could be more diabolic for downgrade. Unlike code > version control, it seems the precondition does not need to exist, at least > for views when you change only the body, not the "view signature". If for > example the c787 upgrade as "create or replace view v1 as select 2, 2" then > it gets messy. I don't even know what downgrade would look like. I assume > alembic would undo the last upgrade applied based on history. > > For a single repository, only one branch gets into master first. So that > defines the order. When there's a fork, it gets more complicated. > > On Tuesday, March 9, 2021 at 6:12:06 PM UTC-5 mik...@zzzcomputing.com wrote: >> >> >> >> On Tue, Mar 9, 2021, at 5:06 PM, 'br...@derocher.org' via sqlalchemy-alembic >> wrote: >>> I'm wondering how to solve an issue. >>> >>> One developer created migration 1efb >>> >>> upgrade: >>> drop view v1 -- moved to query in the code >>> >>> downgrade: >>> create view v1 as select 1 >>> >>> Another developer created a migration c787 >>> >>> upgrade: >>> create or replace view v1 as select 2 >>> >>> downgrade >>> create or replace view v1 as select 1 >>> >>> Now I'm merging them with alembic merge heads. >>> >>> I get revision = 60e8, down_revision = (c787, 1efb). >>> >>> My question is which migration runs first. If 1efb goes first, c787 will >>> fail. If 1efb goes first upgrade is smooth. >>> >>> My concern is some databases are at 1efb and some are at c787. For the >>> database at 1efb, how to I prevent a failure? Can I put some logic in >>> upgrade() (and downgrade()) to prevent this? >> >> seems tricky but does c787 actually fail? it says "create or replace", so >> if "v1" was already dropped it would just create a new view. in the >> other direction, the view is still named "v1" so 1efb will just drop "v1". >> >> if this is not exactly accurate and the name is different or something you >> can always modify 1efb to read "drop view if exists" and "create or replace >> view ". if there's no "drop view if exists" on your target DB then I'd >> stick a quick reflection query in the migration to check if it exists, >> inspect(engine).get_view_definition() should have that. >> >> >>> >>> >>> Thanks, >>> Brian >>> >>> PS: It's actually a bit more complicated than this because I'm merging git >>> forks. >>> >>> -- >>> You received this message because you are subscribed to the Google Groups >>> "sqlalchemy-alembic" group. >>> To unsubscribe from this group and stop receiving emails from it, send an >>> email to sqlalchemy-alem...@googlegroups.com. >>> To view this discussion on the web visit >>> https://groups.google.com/d/msgid/sqlalchemy-alembic/e1fe03f2-bc06-4c76-a75b-e8d0efcf4473n%40googlegroups.com >>> >>> <https://groups.google.com/d/msgid/sqlalchemy-alembic/e1fe03f2-bc06-4c76-a75b-e8d0efcf4473n%40googlegroups.com?utm_medium=email&utm_source=footer>. >> > > -- > You received this message because you are subscribed to the Google Groups > "sqlalchemy-alembic" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to sqlalchemy-alembic+unsubscr...@googlegroups.com. > To view this discussion on the web visit > https://groups.google.com/d/msgid/sqlalchemy-alembic/3873492a-b421-4fe1-b736-9a0d462961a1n%40googlegroups.com > > <https://groups.google.com/d/msgid/sqlalchemy-alembic/3873492a-b421-4fe1-b736-9a0d462961a1n%40googlegroups.com?utm_medium=email&utm_source=footer>. -- You received this message because you are subscribed to the Google Groups "sqlalchemy-alembic" group. To unsubscribe from this group and stop receiving emails from it, send an email to sqlalchemy-alembic+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/sqlalchemy-alembic/de6f0fa8-596b-4c12-9bd5-ed0d687904a8%40www.fastmail.com.
