Having issues with implementing a mutable dict that will react to changes in content. I have managed to setup SQLAlchemy to manage add and delete. However, changes to content of a stored dict doesn't "trigger" update of the SQLAlchemy db.
I found some other questions here on stackoverflow that suggested:
By default SQLAlchemy doesn't track changes inside dict attributes. To make it track changes, you can use the mutable extension:
I followed the example here How to implement mutable PickleTypes that automatically update on change
However, I can't get it to work. In my example, when I change from Column(PickleType) to Column(MutableDict.as_mutable(PickleType)) the SQLAlchemy session no longer finds the object. The code below illustrates what I'm trying to do.
The first code is where I set up the db and the second block I'm trying to add transactions to a person. I manage to add transactions and delete them but not change them. Hence, why I tried with the MutableDict class, but I don't seem to fully understand it.
Setup SQL db: (sqlalchemy_declarative.py)
from sqlalchemy import Column, ForeignKey, Integer, String, PickleType
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.ext.mutable import Mutable
from sqlalchemy.orm import relationship
from sqlalchemy import create_engine
Base = declarative_base()
class MutableDict(Mutable, dict):
@classmethod
def coerce(cls, key, value):
if not isinstance(value, MutableDict):
if isinstance(value, dict):
return MutableDict(value)
return Mutable.coerce(key, value)
else:
return value
def __delitem(self, key):
dict.__delitem__(self, key)
self.changed()
def __setitem__(self, key, value):
dict.__setitem__(self, key, value)
self.changed()
def __getstate__(self):
return dict(self)
def __setstate__(self, state):
self.update(self)
class Person(Base):
__tablename__ = 'person_object'
# Here we define columns for the table person
# Notice that each column is also a normal Python instance attribute.
id = Column(Integer, primary_key=True)
first_name = Column(String, nullable=False)
last_name = Column(String, nullable=False)
def __str__(self): # prints when treated as string (for use interface)
return f"Primary id: {self.id} \n" \
f"First name: {self.first_name}"
class Transactions(Base):
__tablename__ = 'transactions'
# Here we define columns for the table address.
# Notice that each column is also a normal Python instance attribute.
id = Column(Integer, primary_key=True)
transactions = Column(MutableDict.as_mutable(PickleType))
# transactions = Column(PickleType)
person_object_id = Column(Integer, ForeignKey('person_object.id'))
person_object = relationship(Person)
def update(self, tmp_dict):
for key, value in tmp_dict.items():
print(key, value)
setattr(self, self.transactions[f'{key}'], value)
def create_db():
# Create an engine that stores data in the local directory's
# sqlalchemy_example.db file.
engine = create_engine('sqlite:///person.db')
# Create all tables in the engine. This is equivalent to "Create Table"
# statements in raw SQL.
Base.metadata.create_all(engine)
Example code:
from sqlalchemy_declarative import Person, Base, Transactions
from sqlalchemy.orm import sessionmaker
from sqlalchemy import create_engine
import sqlalchemy_declarative as sqlalchemy_declarative
def main():
sqlalchemy_declarative.create_db()
engine = create_engine('sqlite:///person.db')
Base.metadata.bind = engine
db_session = sessionmaker()
db_session.bind = engine
session = db_session()
transaction1 = {'item1': 'banana',
'item2': 'apple',
'item3': 'sugar',
'item4': 'coke',
'item5': 'candy'}
transaction2 = {'item1': 'pizza',
'item2': 'water'}
new_obj = Person(first_name='Bob', last_name='Smith')
session.add(new_obj)
new_transaction = Transactions(transactions=transaction1, person_object=new_obj)
session.add(new_transaction)
new_transaction = Transactions(transactions=transaction2, person_object=new_obj)
session.add(new_transaction)
session.commit()
test = session.query(Transactions).all()
for tmp in test:
print(type(tmp.transactions))
print(tmp.transactions == transaction1)
test2 = session.query(Transactions).filter(Transactions.transactions == transaction1).all()
print(test2)
transaction1 = {'item1': 'banana',
'item2': 'apple',
'item3': 'sugar',
'item4': 'coke',
'item5': 'pineapple'}
test2.update(transaction1)
session.commit()
all_transactions = session.query(Transactions).all()
for tmp in all_transactions:
print(tmp.transactions)
if __name__ == '__main__':
main()
However, the test2 filter doesn't find any transaction that matches the transaction1 dictionary. I suspect this has to do with the fact that the dict are stored as MutableDict and not Dict. But what do I do about that and how do I edit and change my transaction1 after I have added it.
TLDR: I want to change content in my dict that is stored as an ORM using SQLAlchemy.
I realised that I was able to work around my problem by simply not using the .filter method. Hence the example below works just fine.
transaction1 = {'item1': 'banana',
'item2': 'apple',
'item3': 'sugar',
'item4': 'coke',
'item5': 'candy'}
transaction2 = {'item1': 'pizza',
'item2': 'water'}
new_obj = Person(first_name='Bob', last_name='Smith')
session.add(new_obj)
new_transaction = Transactions(transactions=transaction1, person_object=new_obj)
session.add(new_transaction)
new_transaction = Transactions(transactions=transaction2, person_object=new_obj)
session.add(new_transaction)
session.commit()
test = session.query(Transactions).all()
for tmp in test:
print(tmp.transactions)
new_transaction.transactions['item1'] = 'curry banana'
session.commit()
test = session.query(Transactions).all()
for tmp in test:
print(tmp.transactions)
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