Base = declarative_base(cls=Base)
class Training(Entity, Base):
      id = Column(BigInteger, Sequence('training_id_seq', start=1, increment=1))
      meet           = Column(Integer,  primary_key=True, default=Constants.DefaultInteger)
      trdate         = Column(Date,      primary_key=True)
      hrno           = Column(String,    primary_key=True)
      sptime         = Column(DateTime,  primary_key=True)
      part      = Column(String,    nullable=True)
      partno    = Column(String,    nullable=True)

app = Flask('rest-api', template_folder='../templates', static_folder='../static')
CORS(app)

@app.errorhandler(InvalidUsage)
def handle_invalid_usage(error):
     response = jsonify(error.to_dict())
     response.status_code = error.status_code
     return response


if __name__ == "__main__":
app.config['SQLALCHEMY_DATABASE_URI'] = ServerConstants.FUNDAMENTAL_DB
app.config['SQLALCHEMY_TRACK_MODIFICATIONS'] = False
app.register_blueprint(training_api)
app.run(host=ServerConstants.host, port=ServerConstants.port, debug=ServerConstants.debug,
        ssl_context=('cert.pem', 'key.pem'))

training_api = Blueprint('training_api', __name__)

@training_api.route("/training/get", methods=['GET'])
     def get_training():
     **session = Connector.Session()**

     query = session.query(Training)
     query = order_by_latest(query, Training)
     query = add_pagination(request, query)
     trainings = query.all()

     **session.close()**

     return respond_with_json({'trainings': [t.toDict() for t in trainings]})

from sqlalchemy.orm import sessionmaker
from tools import ServerConstants

Session = sessionmaker(bind=ServerConstants.ENGINE)

db = SQLAlchemy(app)
db.session.query(Training)
...

session.connection()