Agency: Preload agency ancestors in the API to fix N+1 query

[Tschuppi81]

Agency: Preload agency ancestors in the API to fix N+1 query

Building the html link of each agency renders its full path, which walks up the parent chain. Only the direct parent was eager loaded, so every ancestor above it was loaded with its own query. Preload the ancestor closure in bulk instead.

TYPE: Performance
LINK: https://seantis-gmbh.sentry.io/issues/7426519446

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 85.43%. Comparing base (31aa86e) to head (f31eb57).
⚠️ Report is 1 commits behind head on master.
✅ All tests successful. No failed tests found.

Additional details and impacted files

Files with missing lines	Coverage Δ
src/onegov/agency/api.py	98.08% <100.00%> (+0.41%)	⬆️

... and 1 file with indirect coverage changes

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[Daverball]

We probably have the same issue for the /api/topics and /api/news endpoints. This is a problem with all models deriving from AdjacencyList. Perhaps it would be better to cache path on the model. We would just need to be careful, that the cache gets updated for all the descendant nodes when moving parent nodes around. But a simple observer on parent and name should get us there, just like we have an observer for maintaining alphabetic sorting of the siblings.