> normally I'd ask what are the conditions under which this row might be > deleted.
In our application, "item" rows can be combined via a "merger" transaction, where one item absorbs the data from other items that are deleted after the merger. Eventually, an item may get "registered" whereby it's reg_number field is assigned a unique number (from an external source), which renders it "permanent", where it can receive merged data, but can no longer itself be merged-into another item. The intentional deletion of a registered item would be an unprecedented event (hasn't yet happened in 200+ years), which would require a manual transaction which would require setting the reg_number field to NULL, then deleting the item. However, accidental deletion *could* happen due to a bug or a faulty data ingest, hence our need for delete protection. Mike, Thanks for your suggestion of using a database trigger and for the code showing how to implement a Core event (which may come in useful in another context). We'll do this one via a database trigger. BTW, We're using PostgreSQL (9.5); can we build the trigger creation/deletion into an alembic migration module? (sorry, probably off-topic) On Thursday, February 9, 2017 at 12:19:26 PM UTC-7, Роберт Шотланд wrote: > > I have a table 'item' that contains a nullable 'reg_number' field that, if > it contains a non-null value, the row must not be deleted. I would normally > implement a SQL delete-trigger to do this, except we would prefer to > maintain a pure SQLAlchemy environment.What would be the best way of > implement this using the ORM? > -- SQLAlchemy - The Python SQL Toolkit and Object Relational Mapper http://www.sqlalchemy.org/ To post example code, please provide an MCVE: Minimal, Complete, and Verifiable Example. See http://stackoverflow.com/help/mcve for a full description. --- You received this message because you are subscribed to the Google Groups "sqlalchemy" group. To unsubscribe from this group and stop receiving emails from it, send an email to sqlalchemy+unsubscr...@googlegroups.com. To post to this group, send email to sqlalchemy@googlegroups.com. Visit this group at https://groups.google.com/group/sqlalchemy. For more options, visit https://groups.google.com/d/optout.
