I'm having problems performing postgresql database operations with Alembic

Question

I use alembic - sqlalchemy during operations on Postgresql database. I run the code and the data is successfully written to the database. Later, when I trigger the code again, this time I see that the data in the database has been completely deleted. When I run the code again, I see that the data is written back to the database. The structure in my code works like this.

1. If the variable in new_data exists in the current database, update it.
2. If the variable in new_data does not exist in the database, write it to the database.
3. This variable does not exist in new_data. Delete this variable if it exists in the database.

I don't know where I'm doing wrong in the code, can you help me?

from ConnectDB import create_db_engine
from Models import VirtualServerCustomModel
import ssl

ssl._create_default_https_context = ssl._create_unverified_context

engine, session = create_db_engine()

class VirtualServerCustomService:
    def __init__(self):
        pass
   
   def get_custom_services(self):
       ........

    def db_process(self):
        new_data = self.get_custom_services()

        db_data = session.query(VirtualServerCustomModel).all()

        # Comparing records in new data records
        for veri in new_data:
            db_verisi_filtreli = session.query(VirtualServerCustomModel).filter_by(vm_name=veri[2]).first()

            if not db_verisi_filtreli:
                # If this record does not exist in the database, add the new record
                session.add(VirtualServerCustomModel(*veri))
            
            else:
                # If there is a record in the database, update it
                db_verisi_filtreli.vcenter = veri[0]
                db_verisi_filtreli.cluster = veri[1]
                db_verisi_filtreli.host = veri[3]
                db_verisi_filtreli.power_state = veri[4]
                db_verisi_filtreli.vlan = veri[5]
                db_verisi_filtreli.ip_address = veri[6]

        # Delete records that are in the database but not in the new data
        for db_verisi_entry in db_verisi:
            if (db_verisi_entry.vcenter,db_verisi_entry.cluster,db_verisi_entry.host,db_verisi_entry.power_state,db_verisi_entry.vlan, db_verisi_entry.ip_address) not in yeni_veri:
                session.delete(db_verisi_entry)

        session.commit()
        session.close()
        
if __name__ == "__main__":
    VirtualServerCustomService().db_process()

If the information in new_data is present in the database, update the record. If the record in new_data is not in the database, write the record to the database. If the record in the database is not in new_data, delete this record from the database.