Re: Encapsulating Complex Business Logic in a Migraiton

On 30/08/2017 6:43 AM, Matt S wrote:
> Standard practice is that you do not refer to "current" models (i.e.
> from app.models import MyModel) in a migration as the migration will
> break when that models changes. This means copying any model-specific
> code into the migration. This becomes impractical when the code needed
> for the migration spans multiple files and models.
>
> How can I encapsulate a complex chain of business logic involving
> multiple models in a migration? For example, if I have instance
> methods on ModelA which calls methods on ModelB, ModelB queries for
> ModelC and calls methods on it. If I use those methods as they exist
> on the models, the migration will eventually break when any of the
> involved Models' schema changes.

In the forwards_func() method after it has been run and done its work,
and if appropriate, I add an extra line after the docstring ... return None

This effectively switches it off and it never does anything ever again.

Obviously you need to be doing stuff you do not wish to roll-back - ever.


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