#1784·NetAlertX

`NEWDEV_devParentRelType` is declared as an array but defaults to a string: "Error decoding JSON object" on every scan, and new devices get `devParentRelType='[]'`

Author: tpanchal-iclrCreated Sep 13, 2026Updated Sep 21, 2026

Labelsbug 🐛next release/in dev image 🚀

What installation are you running?

Production (netalertx) (ghcr.io/jokob-sk/netalertx:26.9.0, also seen on 26.7.1)

Is there an existing issue for this?

I have searched the existing open and closed issues and I checked the docs https://docs.netalertx.com/

The issue occurs in the following browsers

N/A - This is an issue with the backend

Current Behavior

Every scan logs this during Creating new devices, even when no new devices were found (captured with LOG_LEVEL='debug'; debug adds no traceback, only the raw value on the next line):

02:45:19 [Scheduler] run for CSVBCKP: NO
02:45:19 [Scheduler] run for DBCLNP: NO
02:45:19 [Scheduler] run for MAINT: NO
02:45:19 [Scheduler] run for VNDRPDT: NO
02:45:19 [Process Scan]  Processing scan results
02:45:19 [Process Scan]  Exclude ignored devices
02:45:19 [Process Scan] Print Stats
02:45:19 [Scan Stats] Devices Detected.......: 31
02:45:19 [Scan Stats] New Devices............: 0
02:45:19 [Scan Stats] Down Alerts............: 0
02:45:19 [Scan Stats] New Down Alerts........: 0
02:45:19 [Scan Stats] New Connections........: 64
02:45:19 [Scan Stats] Disconnections.........: 0
02:45:19 [Scan Stats] IP Changes.............: 0
02:45:19 [Scan Stats] Scan Method Statistics:
02:45:19     ARPSCAN: 29
02:45:19     INTRNT: 1
02:45:19     local_MAC: 1
02:45:19 [Process Scan] Stats end
02:45:19 [Process Scan] Sessions Events (connect / disconnect)
02:45:20 [Process Scan] Creating new devices
02:45:20 [setting_value_to_python_type] Error decoding JSON object: Expecting value: line 1 column 1 (char 0)
02:45:20 default
02:45:20 [Process Scan] Updating Devices Info
02:45:20 [Process Scan] Updating Sync Hub Node
02:45:20 [Process Scan] Updating devLastConnection from CurrentScan
02:45:20 [Process Scan] Updating Presence from CurrentScan
02:45:20 [Process Scan] Updating NICs presence
02:45:20 [Process Scan] Updating forced presence
02:45:20 [Process Scan] Updating Vendors
02:45:20 [Process Scan] Updating v4 and v6 IPs
02:45:20 [Process Scan] Guessing Icons
02:45:20 [Process Scan] Pairing session events (connection / disconnection) 
02:45:20 [Process Scan] Creating sessions snapshot

The value that fails to parse is default, from NEWDEV_devParentRelType, which is not set in app.conf. Every device created so far has the literal string [] as its relationship type:

SELECT devParentRelType, COUNT(*), MIN(devFirstConnection), MAX(devFirstConnection) FROM Devices GROUP BY 1;
('[]', 95, '2026-04-16 04:25:16', '2026-09-08 02:15:25')

Cause. The setting's type and its default value disagree:

server/plugins/newdev_template/config.json (L1460–1471 at v26.9.0, unchanged on main) declares devParentRelType with "dataType": "array" (select, transformers: ["deviceRelType"]) and "default_value": "default", a plain string.
server/helper.py setting_value_to_python_type(), array branch (L330–333): json.loads("default") raises. The function logs the error and returns [].
server/scan/device_handling.py L723 builds the new-device defaults with '{sanitize_SQL_input(get_setting_value("NEWDEV_devParentRelType"))}', so [] is written into devParentRelType as text.

Why this can't be fixed in config. A valid array value such as NEWDEV_devParentRelType=['default'] parses, but the insert expects a scalar. sanitize_SQL_input() only escapes strings and returns lists unchanged, so the f-string would render '['default']' into the SQL. I read this from the code and did not test it, because it would probably break new-device creation.

UI_theme ('Light') and UI_TOPOLOGY_ORDER ('Name') have the same array-type/string-value mismatch in the Settings table. They don't show up in the backend log, so they may only be read by the frontend.

Expected Behavior

No JSON decode error on scans.
New devices get devParentRelType='default' (or whichever single relationship type is configured).

Suggested fix

Declare devParentRelType as a single-value setting. The column holds one relationship type, and the scan code treats it as a scalar: device_handling.py compares == "nic", and device_instance.py defaults to "default". That means "dataType": "string" with a select element, keeping default_value: "default" and the deviceRelType transformer. Alternatively, keep the array type, change default_value to ["default"], and have device_handling.py insert the first element.

Existing installs would then want a one-time UPDATE Devices SET devParentRelType='default' WHERE devParentRelType='[]'.

Steps To Reproduce

Run 26.9.0 with NEWDEV_devParentRelType not set in app.conf (the default).
Let any device scanner run (e.g. ARPSCAN).
app.log shows Error decoding JSON object … default under Creating new devices, and new rows in Devices have devParentRelType='[]'.

Relevant `app.conf` settings

NEWDEV_devParentRelType   (not set; built-in default used)

docker-compose.yml

yaml

services:
  netalertx:
    image: ghcr.io/jokob-sk/netalertx:26.9.0
    network_mode: host
    cap_add: [NET_ADMIN, NET_RAW, NET_BIND_SERVICE]
    environment:
      - TZ=${TZ}
      - PORT=20211
      - LISTEN_ADDR=127.0.0.1
    volumes:
      - netalertx-config:/data/config
      - netalertx-db:/data/db

Debug or Trace enabled

I confirm I set LOG_LEVEL to debug or trace

Relevant `app.log` section

See Current Behavior (one ARPSCAN + INTRNT cycle at debug level; the lines before it only list LAN devices, omitted for privacy).

Docker Logs

docker logs netalertx for the same scan (it mirrors app.log):

02:45:19 [Scan Stats] New Devices............: 0
02:45:19 [Scan Stats] Down Alerts............: 0
02:45:19 [Scan Stats] New Down Alerts........: 0
02:45:19 [Scan Stats] New Connections........: 64
02:45:19 [Scan Stats] Disconnections.........: 0
02:45:19 [Scan Stats] IP Changes.............: 0
02:45:19 [Scan Stats] Scan Method Statistics:
02:45:19     ARPSCAN: 29
02:45:19     INTRNT: 1
02:45:19     local_MAC: 1
02:45:19 [Process Scan] Stats end
02:45:19 [Process Scan] Sessions Events (connect / disconnect)
02:45:20 [Process Scan] Creating new devices
02:45:20 [setting_value_to_python_type] Error decoding JSON object: Expecting value: line 1 column 1 (char 0)
02:45:20 default
02:45:20 [Process Scan] Updating Devices Info
02:45:20 [Process Scan] Updating Sync Hub Node
02:45:20 [Process Scan] Updating devLastConnection from CurrentScan
02:45:20 [Process Scan] Updating Presence from CurrentScan
02:45:20 [Process Scan] Updating NICs presence
02:45:20 [Process Scan] Updating forced presence
02:45:20 [Process Scan] Updating Vendors
02:45:20 [Process Scan] Updating v4 and v6 IPs
02:45:20 [Process Scan] Guessing Icons
02:45:20 [Process Scan] Pairing session events (connection / disconnection) 
02:45:20 [Process Scan] Creating sessions snapshot

Source: netalertx/NetAlertX

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