Question

I am trying to learn OOP, and I am using the database connection via MySQLdb as my first test. This is what I have so far:

class DBConnection:
    def __init__(self, DB_HOST, DB_PORT, DB_USER, DB_PASSWORD, DB_NAME):
        self.host = DB_HOST
        self.port = DB_PORT
        self.name = DB_NAME
        self.user = DB_USER
        self.password = DB_PASSWORD

    def get_conn(self):
        conn = MySQLdb.connect (host = self.DB_HOST, port = self.DB_PORT,
                                db = DB_NAME, user = DB_USER,
                                passwd = DB_PASSWORD)
        return conn

    def get_cursor(self):
        cursor = self.conn.cursor()
        return cursor

    def get_dict_cursor(self):
        dict_cursor = self.conn.cursor(MySQLdb.cursors.DictCursor)
        return dict_cursor  

Is the above valid? Does self.conn refer to get_conn() or is this an invalid reference. How would I establish a connection to the database and then get a cursor, using the python shell?

Answer 1

You haven’t defined self.conn anywhere. You’re only setting conn as a local inside of get_conn. Define self.conn in your constructor, and then update get_conn to set self.conn. Like this:

class DBConnection:
    def __init__(self, DB_HOST, DB_PORT, DB_USER, DB_PASSWORD, DB_NAME):
        self.host = DB_HOST
        self.port = DB_PORT
        self.name = DB_NAME
        self.user = DB_USER
        self.password = DB_PASSWORD
        self.conn = None

    def get_conn(self):
        self.conn = MySQLdb.connect(host = self.host,
                                    port = self.port,
                                    db = self.name,
                                    user = self.user,
                                    passwd = self.password)

Also, check whether self.conn is set first as opposed to creating a new one each time in get_conn, like this:

def get_conn(self):
    if self.conn is None:
        self.conn = MySQLdb.connect(host = self.host,
                                    port = self.port,
                                    db = self.name,
                                    user = self.user,
                                    passwd = self.password)
    return self.conn

Finally, call the get_conn method like this:

mydbconnobj = DBConnection('localhost',3306,'foouser','foopass','foodbname')
mydbconn = mydbconnobj.get_conn()