Add antipatterns repo

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
+
+
+engine = create_engine('sqlite:///:memory:', echo=True)
+Session = sessionmaker(bind=engine)
+Base = declarative_base()
+
+
+class Toaster(Base):
+    __tablename__ = 'toasters'
+
+    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()