ValueError: Circular Reference in JSON

Why This Happens

JSON is tree-structured and cannot represent circular references. This often occurs with ORM objects that have bidirectional relationships.

The Problem

import json
a = {'name': 'A'}
b = {'name': 'B', 'ref': a}
a['ref'] = b
json.dumps(a)

The Fix

import json
a = {'name': 'A'}
b = {'name': 'B', 'ref': a}
# Select specific fields instead:
json.dumps({'name': a['name']})

Step-by-Step Fix

1. 1

   Remove circular references

   Break cycles before serialization.

2. 2

   Select specific fields

   Build a dict with only needed fields.

3. 3

   Use a custom encoder

   Track seen objects and handle cycles.