Is there a way to pass a class/instance attribute name as a variable?-CodePudding

I am using a class to model and manage a database table, but due to the nature of the data I am usually only updating a single column (attribute) at a time. Is there a way to pass which column (attribute) to update?

Example: Let's say I'm making a log of who has last used an access point.

Base = declarative_base()
class Log(Base):
   __tablename__ = "log"
   id = Column(Integer, primary_key=True)
   access_point = Column(Integer, unique=True)
   admin = Column(String)
   staff = Column(String)
   consult = Column(String)
   visitor = Column(String)

I want a way to pass which user_type (admin/staff/consult/visitor) to an aux function to handle the insertion/updating, including the creation of new access_points, something like:

def db_update(a_p, user_info, user_type):
   q = session.query(Log).filter(Log.access_point == a_p)
   if session.query(q.exists()).scalar():
        stmt = update(Log).where(Log.access_point == a_p).values(user_type=user_info)
        session.execute(stmt)
   else:
        new_point = Log(access_point = a_p, user_type = user_info)
        session.add(new_point)

Is there a way of doing this other than just passing a comparator of some sort to pick the user_type (i.e. "if user_type == 1, update admin" sort of thing)?

CodePudding user response：

Have your function accept the columns names and values as keyword arguments, and pass them directly to the values method or the model's initialiser.

def db_update(a_p, **values):
   q = session.query(Log).filter(Log.access_point == a_p)
   if session.query(q.exists()).scalar():
        stmt = update(Log).where(Log.access_point == a_p).values(**values)
        session.execute(stmt)
   else:
        new_point = Log(access_point = a_p, **values)
        session.add(new_point)

db_update(1, admin='Alice')

If your table should gain additional columns you will be able to update them without changing the function code.

CodePudding user response：

You could use a dictionary.

Here's an example with some mock functions:

def update_admin():
    return 1
def update_staff():
    return 2
def update_consult():
    return 3
def update_visitor():
    return 4


update_dict = {
    'admin': update_admin,
    'staff': update_staff,
    'consult': update_consult,
    'visitor': update_visitor}


print(update_dict['staff']())
# 2

print(update_dict['visitor']())
# 4