On 01/29/2015 03:11 PM, Mike Bayer wrote:
Morgan Fainberg <morgan.fainb...@gmail.com> wrote:
Are downward migrations really a good idea for us to support? Is this downward
migration path a sane expectation? In the real world, would any one really
trust the data after migrating downwards?
It’s a good idea for a migration script to include a rudimentary downgrade
operation to complement the upgrade operation, if feasible. The purpose of
this downgrade is from
Except that is it is code we need to maintain and support. I think we
are making more work for ourselves than the value these scripts provide
justify.
a practical standpoint helpful when locally testing a specific, typically
small series of migrations.
A downgrade however typically only applies to schema objects, and not so much
data. It is often impossible to provide downgrades of data changes as it is
likely that a data upgrade operation was destructive of some data. Therefore,
when dealing with a full series of real world migrations that include data
migrations within them, downgrades are typically impossible. I’m getting the
impression that our migration scripts have data migrations galore in them.
So I am +1 on establishing a policy that the deployer of the application would
not have access to any “downgrade” migrations, and -1 on removing “downgrade”
entirely from individual migrations. Specific migration scripts may return
NotImplemented for their downgrade if its really not feasible, but for things
like table and column changes where autogenerate has already rendered the
downgrade, it’s handy to keep at least the smaller ones working.
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