Wsrtjtyk

I try to save some columns (eg: tags, models) with JSON encoded string.

And I hope to always keep then decoded in use.

I have read some refers to add configs to disable autocommit and autoflush , but it doesn't work.

While the instance was added into db.session and then changed value , orm still try to commit an UPDATE OPERATION and then raise TypeError.

Here is my code.

```python

import json

from sqlalchemy import orm

from flask_sqlalchemy import SQLAlchemy



session_options = dict(

    bind=None,

    autoflush=False,

    autocommit=False,

    expire_on_commit=False,

)

db = SQLAlchemy(session_options=session_options)





class Sample(db.Model):

    id = db.Column(db.Integer, primary_key=True, autoincrement=True)

    # tags, models : string of json.dumps(array)

    tags = db.Column(db.String(128), default='')

    models = db.Column(db.String(128), default='')



    def __init__(self, **kwargs):

        cls = self.__class__

        super(cls, self).__init__(**kwargs)

        self.formatting()



    @orm.reconstructor

    def init_on_load(self):

        self.formatting()



    def formatting(self):

        self.tags = json.loads(self.tags)

        self.models = json.loads(self.models)



    def save(self):

        self.tags = json.dumps(self.tags)

        self.models = json.dumps(self.models)



        db.session.add(self)

        db.session.commit()



        self.formatting()

        ## fixme !!!

        ## formatting after saved will cause auto-commit and raise TypeError 

```

Thank you :)

ps: Flask-SQLAlchemy==2.3.2

This error was raised by lacking called db.session.close() after db.session.commit()

I was told that db.session.close() is automatically called in db.session.commit(). And the real has denied my cognition.

And I try to refer the source code of sqlalchmey, and then I find the db.session is an instance of sqlalchemy.orm.scoping.scoped_session, NOT sqlalchemy.orm.SessionTransaction.

Here is the source code in sqlalchemy.orm.SessionTransaction

```python

def commit(self):

    self._assert_active(prepared_ok=True)

    if self._state is not PREPARED:

        self._prepare_impl()



    if self._parent is None or self.nested:

        for t in set(self._connections.values()):

            t[1].commit()



        self._state = COMMITTED

        self.session.dispatch.after_commit(self.session)



        if self.session._enable_transaction_accounting:

            self._remove_snapshot()



    self.close()

    return self._parent

```

It’s really confusing.

If you want to repeat this Error, here is Test code:

```python

"""

# snippet for testing <class:Sample>

"""



from flask import Flask

app = Flask(__name__)

app.config.from_mapping(

    SQLALCHEMY_ECHO=True,

    SQLALCHEMY_TRACK_MODIFICATIONS=False,

    SQLALCHEMY_DATABASE_URI='sqlite:///test_orm.sqlite.db',

)



db.init_app(app=app)

db.app = app

db.create_all()



d1 = dict(

    tags='["python2","flask"]',

    models='["m1"]'

)

m1 = Sample(**d1)

print(1111, type(m1.tags), m1.tags)

m1.save()

print(1112, type(m1.tags), m1.tags)

dm1 = Sample.query.filter(Sample.id == m1.id).all()[0]

print(1113, dm1, type(dm1.tags), dm1.tags)



## fixme[Q1] !!!

## if not continue with $d2, it won't raise error of UPDATE $d1



d2 = dict(

    tags='["python3","flask"]',

    models='["m2", "m3"]'

)

m2 = Sample(**d2)

print(2221, type(m2.tags), m2.tags)



## fixme[Q1] !!!

# db.session.close()

## If session was not closed, error raise here.



m2.save()

print(2222, type(m2.tags), m2.tags)

dm2 = Sample.query.filter(Sample.id == m2.id).all()[0]

print(2223, dm2, type(dm2.tags), dm2.tags)

```

Thank you for your read ，wish to disabuse your same confusion.