[OSM-dev] Relations referencing deleted elements

[mmd]

On 17/04/2020 08:10, Marc Labrecque wrote:
> Since I've only first run into this issue in the past week, I was
> wondering if there is a bug that was recently introduced which is
> allowing these elements to be deleted even though they are still
> referenced by a relation.

This bug has been around for almost a year now, and occurred under very
special circumstances only:

- A user wants to remove the last member of a child relation

- This child relation is part of a 3-level nested relation
(child/parent/grandparent)

In the case of the second example mentioned, the grandparent corresponds
to the National Expressways of South Korea (relation 6818098), which
includes route_master relation 4424722 (parent), which in turn
references relations 4424718, 4424720, and 4424721 as children.

- iD deletes both child and parent relations, but for some reason didn't
adjust the grandparent->parent dependency. This is being addressed in
another GitHub issue.

In the API request, only child and parent relations were to be deleted
using the if-unused="true" flag. This flag is set by some editors like
iD, Potlatch, and GoMap!! to suppress error messages for already deleted
objects. IIRC it has been introduced as a convenience feature for
Potlatch back in the days.

- CGImap deleted the child, although it was still required by the
grandparent->parent dependency. This only happened in case the API was
called with if-unused="true".

An updated CGImap 0.8.2 release including a fix for this issue has been
deployed already.

Thanks again for providing a thorough analysis of the issue.

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