oca-ocb-core/docs/QWEBJSON_CIRCULAR_REFERENCE.md

QwebJSON Circular Reference Bugfix

Problem

When loading the Odoo 19 web client, the web.webclient_bootstrap QWeb template fails with:

ValueError: Circular reference detected

at the line:

<t t-out="json.dumps(session_info)"/>

Root Cause

The QwebJSON.dumps() default handler in odoo/addons/base/models/ir_qweb.py returned non-serializable objects unchanged:

# Original (broken)
class QwebJSON(json.JSON):
    def dumps(self, *args, **kwargs):
        prev_default = kwargs.pop('default', lambda obj: obj)
        return super().dumps(*args, **kwargs, default=(
            lambda obj: prev_default(str(obj) if isinstance(obj, QwebContent) else obj)
        ))

When the JSON encoder encounters a non-serializable type (e.g. ReadonlyDict, lazy, datetime, bytes, Domain), it calls the default handler. The handler returns the object unchanged (since it's not QwebContent). The encoder tries to serialize it again, gets the same object back, and raises "Circular reference detected."

This is a latent bug in the Odoo 19 core. In vanilla Odoo it rarely triggers because session_info values are typically JSON-serializable. However, any module (OCA or custom) that introduces a non-serializable type into session_info or any other QWeb JSON-serialized context will expose this bug.

Fix

Use odoo.tools.json.json_default() as the fallback for non-QwebContent objects:

# Fixed
class QwebJSON(json.JSON):
    def dumps(self, *args, **kwargs):
        prev_default = kwargs.pop('default', lambda obj: obj)
        return super().dumps(*args, **kwargs, default=(
            lambda obj: prev_default(str(obj) if isinstance(obj, QwebContent) else json.json_default(obj))
        ))

json_default() (from odoo/tools/json.py) properly handles:

• datetime -> string via fields.Datetime.to_string()
• date -> string via fields.Date.to_string()
• lazy -> resolved value
• ReadonlyDict -> regular dict
• bytes -> decoded string
• Domain -> list
• anything else -> str(obj)

File Changed

• odoo-bringout-oca-ocb-base/odoo/addons/base/models/ir_qweb.py (class QwebJSON)

Date

2026-03-10