SQLAlchemy model manager

manager.py

from sqlalchemy.orm import Session


class Manager:
    
    def __init__(self, Model, database: Session):
        self.db = database
        self.Model = Model
        self._query = {}  # Instantiate a query, update it on get/filter call
        
    def __str__(self):
        return "%s_%s" % (self.__class__.__name__, self.Model.__name__)
    
    def __len__(self):
        return self.__fetch().count()
    
    def __iter__(self):
        for obj in self.__fetch():
            yield obj
    
    def __getitem__(self, item):
        return list(self)[item]
    
    def update_query(self, query):
        self._query.update(query)
    
    def __fetch(self):
        return self.db.query(self.Model).filter_by(**self._query)

    def get(self, **query):
        self.update_query(query)
        return self.__fetch().first()

    def filter(self, **query):
        self.update_query(query)
        return self

    def create(self, **kwargs):
        obj = self.Model(**kwargs)
        self.save(obj)
        return obj

    def save(self, obj):
        self.db.add(obj)
        self.db.commit()
        self.db.refresh(obj)

    def all(self):
        return self

You can use this as a manager for your SQLAlchemy model

class Market(Base):
    __tablename__ = "markets"
    id = Column(Integer, primary_key=True, index=True)
    name = Column(String(50))
    
    @classmethod
    def objects(cls):
        return Manager(cls, SessionLocal())