Expression to concatenate Django Postgres JSONField

concat_json_expression.py

from django.db.models.expressions import CombinedExpression, F, Value
from django.contrib.postgres.fields import JSONField


expression =  CombinedExpression(
    F('my_json_field'), 
    '||', 
    Value({'fizz': 'buzz'}, JSONField())
)

nice!
I wanted to extend the JSON field looking up another field, so I used it with JSONObject like this

from django.db.models.functions import JSONObject
from django.db.models.expressions import CombinedExpression, F

# {
#   "my_json_field": { "foo": "bar" },
#   "non_json_field": "buzz"
# }

expression =  CombinedExpression(
    F('my_json_field'), 
    '||', 
    JSONObject(fizz=F('non_json_field'))
)

# {
#   "foo": "bar",
#   "fizz": "buzz"
# }

Does this overwrite keys that already exist in the JSON field?

yes, it's just the Postgres jsonb concatenation operator (||).

Concatenating two objects generates an object containing the union of their keys, taking the second object's value when there are duplicate keys.