Python - how to implement Bridge (or Adapter) design pattern?


Question

I'm struggling with implementing the Bridge design pattern (or an alternative such as Adapter) in Python

I want to be able to write code like this to dump database schemas based on a supplied URL:

urls = ['sqlite://c:\\temp\\test.db', 'oracle://user:password@tns_name'];
for url in urls:
    db = Database(url);
    schema = db.schema()

I've got classes defined as

class Database():
    def __init__(self, url):
        self.db_type = string.split(self.url, "://")[0]

class Oracle():
    def schema(self):
        # Code to return Oracle schema

class SQLite():
    def schema(self):
        # Code to return SQLite schema

How can I "glue" these 3 classes together so I can get the first code block to execute correctly? I've Googled around, but must be having a thick day as it's just not coming together in my mind...

Thanks in advance

1
14
6/24/2009 1:36:22 PM

Accepted Answer

Use a Factory pattern instead:

class Oracle(object):
  ...

class SQLite(object):
  ...

dbkind = dict(sqlite=SQLite, oracle=Oracle)

def Database(url):
  db_type, rest = string.split(self.url, "://", 1)
  return dbkind[db_type](rest)
26
5/25/2009 4:16:29 AM

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