Create a Python User() class that both creates new users and modifies existing users

Question

I'm trying to figure out the best way to create a class that can modify and create new users all in one. This is what I'm thinking:

class User(object):

    def __init__(self,user_id):
      if user_id == -1
          self.new_user = True
      else:
          self.new_user = False

          #fetch all records from db about user_id
          self._populateUser() 

    def commit(self):
        if self.new_user:
            #Do INSERTs
        else:
            #Do UPDATEs

    def delete(self):
        if self.new_user == False:
            return False

        #Delete user code here

    def _populate(self):
        #Query self.user_id from database and
        #set all instance variables, e.g.
        #self.name = row['name']

    def getFullName(self):
        return self.name

#Create a new user
>>u = User()
>>u.name = 'Jason Martinez'
>>u.password = 'linebreak'
>>u.commit()
>>print u.getFullName()
>>Jason Martinez

#Update existing user
>>u = User(43)
>>u.name = 'New Name Here'
>>u.commit()
>>print u.getFullName()
>>New Name Here

Is this a logical and clean way to do this? Is there a better way?

Thanks.

Answer 1

Small change to your initializer:

def __init__(self, user_id=None):
      if user_id is None:

Answer 2

Off the top of my head, I would suggest the following:

1: Use a default argument None instead of -1 for user_id in the constructor:

def __init__(self, user_id=None):
    if user_id is None:
         ...

2: Skip the getFullName method - that's just your Java talking. Instead use a normal attribute access - you can convert it into a property later if you need to.

Answer 3

What you are trying to achieve is called Active Record pattern. I suggest learning existing systems providing this sort of things such as Elixir.

Answer 4

You can do this with metaclasses. Consider this :

class MetaCity:
    def __call__(cls,name):
        “”“
            If it’s in the database, retrieve it and return it
            If it’s not there, create it and return it
        ““”
            theCity = database.get(name) # your custom code to get the object from the db goes here
            if not theCity:
                # create a new one
                theCity = type.__call__(cls,name)

        return theCity

class City():
    __metaclass__ = MetaCity
    name   = Field(Unicode(64))

Now you can do things like :

paris = City(name=u"Paris") # this will create the Paris City in the database and return it.
paris_again = City(name=u"Paris") # this will retrieve Paris from the database and return it.

from : http://yassinechaouche.thecoderblogs.com/2009/11/21/using-beaker-as-a-second-level-query-cache-for-sqlalchemy-in-pylons/