Fix #206 - Overtaking events are deleted now, when the parent track is deleted

[boldt]

Summary

This fixes #206. When I delete a track, the event points on the public map are deleted as well.

@gluap @opatut I dont know how to add migrations. Please support. Thanks.

Solution

This sounds exaclty like our problem:

I cannot get a simple cascade delete to operate correctly -- if a parent element is a deleted, the children persist, with null foreign keys

That thread also provides a solution:

Setting the passive_deletes=True prevents SqlAlchemy from NULLing out the foreign keys.

This is, what is MR does: It adds passive_deletes=True to the relationships.

See:

• https://stackoverflow.com/a/38770040/605890
• https://docs.sqlalchemy.org/en/14/orm/cascades.html

[sonarcloud]

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[gluap]

@boldt this one shouldn't need a migration, the relationship shouldn't change the schema. If I understand this correctly the default behavior of sqlalchemy applied to our situation is to null the foreignkey in the overtaking_event table before deleting the track from the track table. As the reference isn't there when the track is deleted, nothing propagated. This also explains why deleting a track via command line didn't reproduce the issue.