it looks like Postgresql 9.5+ has a new function jsonb_set that does this, this 
can be used with func. If you aren't on pg9.5 you might have to update the 
whole value.

full POC below

from sqlalchemy import Column
from sqlalchemy import create_engine
from sqlalchemy import func
from sqlalchemy import Integer
from sqlalchemy import type_coerce
from sqlalchemy.dialects.postgresql import JSONB
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import Session

Base = declarative_base()


class A(Base):
 __tablename__ = "a"

 id = Column(Integer, primary_key=True)
 data = Column(JSONB)


e = create_engine("postgresql://scott:tiger@localhost/test", echo=True)
Base.metadata.drop_all(e)
Base.metadata.create_all(e)

s = Session(e)

data = {
 "preference": {
 "android": {"software_update": "true", "system_maintenance": "true"},
 "ios": {"software_update": "true", "system_maintenance": "true"},
 }
}

a1 = A(data=data)
s.add(a1)
s.commit()

s.query(A).update(
 {
 A.data: func.jsonb_set(
 A.data,
 "{preference,android}",
 type_coerce(
 {"software_update": "false", "system_maintenance": "false"},
 JSONB,
 ),
 )
 },
 synchronize_session="fetch",
)

assert a1.data["preference"]["android"] == {
 "software_update": "false",
 "system_maintenance": "false",
}




On Thu, Jul 4, 2019, at 7:44 AM, NanthaKumar Loganathan wrote:
> Hi , I have below jsonb blob which i wanted to update subset value.
> 
> {
>  "preference": {
>  "android": {
>  "software_update": "true",
>  "system_maintenance": "true"
>  },
>  "ios": {
>  "software_update": "true",
>  "system_maintenance": "true"
>  }
>  }
> }
> 
> how to i update only "android" blob which is inside "preference"
> can someone help here with sqlalchemy query?
> the following snippet doesnt worked for me
> 
> app_name = 'android'
> pref = {"software_update": "false", "system_maintenance": "false"}
> qu = session.query(SystemSubscription).filter(SystemSubscription.username == 
> 't...@gmail.com').update(
>     {SystemSubscription.preference: cast(
>         cast(SystemSubscription.preference[app_name], 
> JSONB).concat(func.jsonb_build_object(app_name, json.dumps(pref))),
>         JSON)}, synchronize_session="fetch")
> 

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To post example code, please provide an MCVE: Minimal, Complete, and Verifiable 
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