Per‑sender duplicate signal registration causes CounterCacheField double‑counting #963

New Issue

MrUnknownDE · 2026-04-05T19:15:00+02:00

MrUnknownDE commented

2026-04-05 19:15:00 +02:00

Originally created by @pheus on 10/28/2025

NetBox Edition

NetBox Community

NetBox Version

v4.4.4

Python Version

3.10

Steps to Reproduce

Have two CounterCacheField registrations that both use dcim.Device as the child model, for example:
- DeviceType.device_count (count devices by device_type)
- VirtualChassis.member_count (count devices by virtual_chassis)
Create or delete a single Device.

Expected Behavior

Each create/delete updates the relevant counters once (e.g., device_count += 1 on create, device_count -= 1 on delete).

Observed Behavior

Counters update twice (e.g., +2 on create, -2 on delete).

Root Cause

In the counters registry (utilities/counters.py), the dispatch_uid for signal connections is currently formed from the model and field (conceptually {model._meta.label}.{field.name}).
When multiple counters share the same sender (e.g., Device via device_type_id and virtual_chassis_id), this yields different UIDs, so Django connects the same receiver multiple times for that sender. A single post_save emission for Device is then handled twice, doubling the counter updates.

This was uncovered while developing FR #19523 (instance/usage filtering), which depends on accurate device_count/module_count values.

*Originally created by @pheus on 10/28/2025* ### NetBox Edition NetBox Community ### NetBox Version v4.4.4 ### Python Version 3.10 ### Steps to Reproduce 1. Have two `CounterCacheField` registrations that both use **`dcim.Device`** as the child model, for example: - `DeviceType.device_count` (count devices by `device_type`) - `VirtualChassis.member_count` (count devices by `virtual_chassis`) 2. Create or delete a single `Device`. ### Expected Behavior Each create/delete updates the relevant counters **once** (e.g., `device_count += 1` on create, `device_count -= 1` on delete). ### Observed Behavior Counters update **twice** (e.g., `+2` on create, `-2` on delete). ### Root Cause In the counters registry (`utilities/counters.py`), the `dispatch_uid` for signal connections is currently formed from the **model and field** (conceptually `{model._meta.label}.{field.name}`). When multiple counters share the **same sender** (e.g., `Device` via `device_type_id` and `virtual_chassis_id`), this yields **different UIDs**, so Django connects the **same** receiver **multiple times** for that sender. A single `post_save` emission for `Device` is then handled twice, doubling the counter updates. ### Related Work This was uncovered while developing FR **#19523** (instance/usage filtering), which depends on accurate `device_count`/`module_count` values.

MrUnknownDE closed this issue

2026-04-05 19:15:00 +02:00

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Branches Tags

main

21455-sql-indexes-audit

21357-register-model-actions

feature

20924-plugin-ui-components

21766-improve-test-coverage-for-sortable-table-columns

21157-export-template-public-models

21025-pre-render-config-contexts

21364-swagger

feature-ip-prefix-link

20911-dropdown-3

fix_module_substitution

21160-filterset

20911-dropdown-2

20044-elevation-stuck-lightmode

7604-filter-modifiers-v3

20660-script-load

19724-graphql

14884-script

19720-macaddress-interface-generic-relation

fix-19669-api-image-download

7604-filter-modifiers

19275-fixes-interface-bulk-edit

fix-17794-get_field_value_return_list

11507-show-aggregate-and-rir-on-api

9583-add_column_specific_search_field_to_tables

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Reference: github/netbox#963