professional-programming/antipatterns/sqlalchemy-examples/exists.py

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from sqlalchemy import create_engine
from sqlalchemy import Column, Integer, String
from sqlalchemy.orm import sessionmaker
from sqlalchemy.ext.declarative import declarative_base
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engine = create_engine("sqlite:///:memory:", echo=True)
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Session = sessionmaker(bind=engine)
Base = declarative_base()
class Toaster(Base):
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__tablename__ = "toasters"
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id = Column(Integer, primary_key=True)
name = Column(String)
color = Column(String)
def toaster_exists_bad(toaster_id):
session = Session()
return bool(session.query(Toaster).filter_by(id=toaster_id).first())
def toaster_exists_good(toaster_id):
session = Session()
query = session.query(Toaster).filter_by(id=toaster_id)
return session.query(query.exists()).scalar()
def main():
Base.metadata.create_all(engine)
toaster_exists_bad(1)
toaster_exists_good(2)
if __name__ == "__main__":
main()