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<TITLE>Re: [Seaside] Re: Smalltalk design advice - how toimplementgenericbi-directional pointers?</TITLE>
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<P><FONT SIZE=2>Except favourite pizza is usually some kind of aggregate of team members preferences depending on their number, seniority and drunkenness.<BR>
<BR>
Cheers!<BR>
<BR>
-Boris (via BlackBerry)<BR>
<BR>
----- Original Message -----<BR>
From: seaside-bounces@lists.squeakfoundation.org <seaside-bounces@lists.squeakfoundation.org><BR>
To: Seaside - general discussion <seaside@lists.squeakfoundation.org><BR>
Sent: Mon Dec 24 21:33:04 2007<BR>
Subject: Re: [Seaside] Re: Smalltalk design advice - how toimplementgenericbi-directional pointers?<BR>
<BR>
<BR>
Assume you have a collection of all the projects that interest you; <BR>
each project object (oh and be careful - there's a good chance that <BR>
there is a class called Project already in existence, so choose a <BR>
slightly more specific name) would likely instance variable for its <BR>
name, accounting code (accountants love their code numbers), manager, <BR>
purpose, company division, favourite pizza etc and, most importantly a <BR>
collection of employees assigned to it.<BR>
<BR>
In your project class, implement a method to query the collection of <BR>
employees to find out if a particular employee is assigned. As it <BR>
happens, the message #detect: already exists for this purpose; it <BR>
works like this -<BR>
Given a collection containing fred, jim, bill, sheela, alice<BR>
myCollection detect:[:element| element name = 'bill']<BR>
would return the first actual employee object which responded with <BR>
true - so be careful with your tests since you may give yourself <BR>
false positives! Let us assume your test is adequately careful, <BR>
perhaps because you actually test for identity rather than just a <BR>
partial name; you will get back the appropriate employee object.<BR>
<BR>
Unless it is not there - then you get an error. Whoops, better to use <BR>
#detect:ifNode: in that case. Like this<BR>
myCollection detect:[employee| employee == theEmployeeIWant] ifNone:<BR>
[nil]<BR>
that way you either get the employee or nil.<BR>
<BR>
So far then we can ask a particular project if a certain employee is <BR>
working on it. What about finding all the project s/he is working on? <BR>
There's a bunch of ways of iterating across collections and gathering <BR>
results - take a look at the Collection class and in particular the <BR>
'enumerating' protocol. In this case the #select: message is a <BR>
reasonable choice since it builds a collection of all the elements <BR>
that answer true when sent to the block -<BR>
companyProjects select:[:proj| proj teamIncludes: <BR>
theEmpoyeeOfInterest]<BR>
<BR>
So - we have a nice encapsulated way of asking the core question and a <BR>
nice way of building our list of projects the 'fred' works on. It's <BR>
not at all hard to extend this to find all the projects involving <BR>
several people, or a project that 'jim' isn't working on etc. There <BR>
are lots of useful enumeration methods for youto make use of.<BR>
<BR>
Please, please don't give in to the temptation to give the <BR>
CompanyProject class a method that simply returns the collection of <BR>
employees and then just use some awful C programmer crap to treat <BR>
objects as mere arrays of data. Encapsulation will save you time, <BR>
effort and sanity in the long run. Any time you see code looking like<BR>
things whotsits dooberries do:[db| db subelements do:[ ......<BR>
run, screaming, away.<BR>
<BR>
tim<BR>
--<BR>
tim Rowledge; tim@rowledge.org; <A HREF="http://www.rowledge.org/tim">http://www.rowledge.org/tim</A><BR>
Useful random insult:- Proof that evolution CAN go in reverse.<BR>
<BR>
<BR>
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