OOP: How to implement listing al 'Employees'.

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Petar

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Dec 28, 2007, 7:05:59 AM12/28/07
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I was just wondering.

What if you have a 'Employees' class and you want to list all the
employees. Currenlty i'm seeing to possibilities:

- create a 'listAll' function inside the class which returns all the
employees in a array.
- create multiple instances, putting them in a array, by calling the
Employees class multiple times in a loop (thus not creating a listAll
function in the class).

What is the better way of doing this? And should a class always
reference only on 'item'?

Thank in advance.

Bjoern Schliessmann

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Dec 28, 2007, 7:40:30 AM12/28/07
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Petar wrote:
> What is the better way of doing this? And should a class always
> reference only on 'item'?

It fully depends on what you want to do in your program. If you just
want to have a list of employees, a list or dict will suffice. If
you need a full-fledged employee database, an "Employees" class may
be a good API.

Regards,


Björn

--
BOFH excuse #83:

Support staff hung over, send aspirin and come back LATER.

Petar

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Dec 28, 2007, 8:19:18 AM12/28/07
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On 28 dec, 13:40, Bjoern Schliessmann <usenet-

It's a pure hypothetical question about where to put the function for
the list of employees when already having a Employee class.

Do I make it a method of the class, or do i create a instance of the
class for every employee (sitting inside a list)?

Bruno Desthuilliers

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Dec 28, 2007, 8:38:05 AM12/28/07
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Bjoern Schliessmann a écrit :

> Petar wrote:
>> What is the better way of doing this? And should a class always
>> reference only on 'item'?
>
> It fully depends on what you want to do in your program. If you just
> want to have a list of employees, a list or dict will suffice. If
> you need a full-fledged employee database, an "Employees" class may
> be a good API.

If you need a full-fledged employee database, a RDBMS may be a good API.
And if you insist on having it the OO way, have a look at SQLAlchemy.

My 2 cents...

Bruno Desthuilliers

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Dec 28, 2007, 1:33:00 PM12/28/07
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Petar a écrit :

> On 28 dec, 13:40, Bjoern Schliessmann <usenet-
> mail-0306.20.chr0n...@spamgourmet.com> wrote:
>
>>Petar wrote:
>>
>>>What is the better way of doing this? And should a class always
>>>reference only on 'item'?
>>
>>It fully depends on what you want to do in your program. If you just
>>want to have a list of employees, a list or dict will suffice. If
>>you need a full-fledged employee database, an "Employees" class may
>>be a good API.
>>
(snip)

>
> It's a pure hypothetical question about where to put the function for
> the list of employees when already having a Employee class.

The problem with "pure hypothetical" questions is that they usually have
no single good answer, and sometimes even no answer at all.

Now since you're talking database, the most common patterns seems to
have either some YourDomainClassNameHere methods to query instances, or
some module/singleton object providing such querying interfaces for the
whole app (or FWIW to provide both, the first calling on the second...).

> Do I make it a method of the class, or do i create a instance of the
> class for every employee (sitting inside a list)?

If you have an Employee class, I don't get how you would avoid creating
an instance for each and every, well, instance ? Unless you're thinking
about something like MS "recordsets" ? But then, you don't need any
domain class at all...

Bruno Desthuilliers

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Dec 28, 2007, 1:34:07 PM12/28/07
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Petar a écrit :
(snip)

> should a class always
> reference only on 'item'?

???

I'm afraid I didn't get this part of the question.

Message has been deleted

Petar

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Dec 29, 2007, 4:53:38 AM12/29/07
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On 28 dec, 19:42, Dennis Lee Bieber <wlfr...@ix.netcom.com> wrote:
> On Fri, 28 Dec 2007 04:05:59 -0800 (PST), Petar <peros...@gmail.com>
> declaimed the following in comp.lang.python:
>         Bottom-up responses...
>
>         Unless you are contaminated by Java's need for a class to hold
> static functions, classes are just templates for an undefined object.
> You create an instance of the class to create a defined object. It is
> not common in Python to create a class that is not meant to be
> instantiated at least once (something that is just static methods is
> probably easier implemented as an import module with plain functions and
> module level globals).
>
>         Now, by "name", an "Employees" (plural s) class, to me, implies a
> class to represent a group of employees -- as a group! It would NOT have
> methods or members (both of which are just attributes in generic Python
> hissing) that refer to information about any specific employee -- such
> information should be part of an "Employee" (no S) class.
>
> aDept = Employees(dept="Finance")
> aDept.manager = Employee(name="John Dont", ID=3141596, phone="123-4567")
> aDept.addEmployee(Employee(name=....))
> aDept.addEmployee(Employee(...))
> ...
>         Note that this does not enforce any particular storage concept. The
> Employees (with the S) class could be using a list to store each
> employee, or a dictionary (maybe keyed by ID), or even an RDBM with a
> join (where one has tables for, say, department, employee, and
> intersection linking department to employee):
>
> select e.* from employees as e
> inner join dept_employee as de
> on de.empID = e.ID
> inner join departments as d
> on d.id = de.deptID
> where d.name = "Finance";
>
> aBody = aDept.employee(id=....)
>
> aDept.removeEmployee(id=...)
>
> aDept.printEmployees()
>
>         If all you need is a "list" of raw employees, with no meaning
> associated to the list... Then just use a list...
>
> aList = []
> aList.append(Employee(name=...))
> aList.append(Employee(...))
>
> for e in aList:
>         e.printEmployee()
> --
>         Wulfraed        Dennis Lee Bieber               KD6MOG
>         wlfr...@ix.netcom.com             wulfr...@bestiaria.com
>                 HTTP://wlfraed.home.netcom.com/
>         (Bestiaria Support Staff:               web-a...@bestiaria.com)
>                 HTTP://www.bestiaria.com/

I'm sorry if my question wasn't clear enough. But I think it has been
answered.

Let me explain how I got to this question. I had written een Article
class which handled the articles that I had. On a certain page I
wanted to show all the articles. That got me wondering about what to
do. Should I make a method in my Article.class which returned multiple
articles, or should I just use my current Article.class and fill a
list (with a loop) with articles. The first solution thus meaning
writing another method, the latter method to just use the current
Article.class and call it multiple times.

The post of Dennis made me realize of another solution though. To
create another class called Articles which return multiple articles.
The only problem I forsee with this that's it's gonna be a very empty
class.

Thank you all for your response, it has pointed me in the right
direction.

Marc 'BlackJack' Rintsch

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Dec 29, 2007, 6:10:41 AM12/29/07
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On Sat, 29 Dec 2007 01:53:38 -0800, Petar wrote:

> The post of Dennis made me realize of another solution though. To
> create another class called Articles which return multiple articles.
> The only problem I forsee with this that's it's gonna be a very empty
> class.

Then maybe it should not be a class. Maybe a function returning
`Article`\s would be enough. This is not Java, not everything has to be
stuffed into classes.

Ciao,
Marc 'BlackJack' Rintsch

Mike Orr

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Dec 31, 2007, 3:53:06 PM12/31/07
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On Dec 29, 1:53 am, Petar <peros...@gmail.com> wrote:

> Let me explain how I got to this question. I had written een Article
> class which handled the articles that I had. On a certain page I
> wanted to show all the articles. That got me wondering about what to
> do. Should I make a method in my Article.class which returned multiple
> articles, or should I just use my current Article.class and fill a
> list (with a loop) with articles. The first solution thus meaning
> writing another method, the latter method to just use the current
> Article.class and call it multiple times.

A class method would be ideal for this if you have no other reason to
create an Articles class:

@classmethod
def all(class_):
ret = []
for a in THE_ARTICLES:
article = class_(a)
ret.append(article)
return ret

Definitely don't use an instance method, which is expected to operate
on one article without making additional Article instances.

Mark 'Blackjack' Rintsch wrote:
> Then maybe it should not be a class. Maybe a function returning
> `Article`\s would be enough. This is not Java, not everything
> has to be stuffed into classes.

True, but this function is logically related to the Article class, so
it's convenient to put them together. Then the user can just "from __
import Article" rather than "from __ import Article, get_all_articles,
what_was_that_other_function?".

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