On 02/24/2014 08:19 PM, Sangeeth Saravanaraj wrote:
Sorry, I should have described what I was trying!
I want to create a decorator which should do the following things:
- When an object of the decorated class is created, the objects name
(say the value of the incoming "id" argument) should be stored as a record
in a table in a database.
- When an object of the decorated class is deleted, the record with this
deleted objects name (i.e. object.id) should be removed from the table.
You can safely assume that all the database operations are working fine!
Now, for example - consider the following snippet:
@saveme
class A(object):
def __init__(self, id):
self.id = id
@saveme
class B(object):
def __init__(self, id):
self.id = id
"saveme" should do what I have explained earlier.
a1 = A("A1")
a2 = A("A2")
a3 = A("A3")
b1 = B("B1")
b2 = B("B2")
At this point if I query and print all the records in a table, I should get
the following:
output: ["A1", "A2", "A3", "B1", "B2"]
del a1
del a2
del a3
del b1
del b2
At this point, all entries in the table should be deleted; query should
return an empty list!
And, I want to highlight that the classes that are being decorated with
"saveme" can de derived classes too!
What is the best way to do this?!
Thank you,
Sangeeth
Your problem looks like a typical "crosscutting" (transversal) concern addressed
by AOP (Aspect Oriented Programming). Their usual example is in fact logging.
Look at the wikipedia page:
https://en.wikipedia.org/wiki/Aspect-oriented_programming
Not that it would help you solve it _in python_, but this may serve at least to
better understand what kind of problem you are actually facing; and why it is
annoying in programming (with common languages); what may be your options.
[I have no better approach than yours, using magic metamethods, and a decorator
to wrap it all.]
d
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