What design pattern to use

  • Thread starter Thread starter Smith
  • Start date Start date
S

Smith

Hi

I couldn't find a newsgroup discussing software architecure so now I'm trying
my luck here. Please redirect me if there's a newsgroup about architecture
:-)

I've got the following scenario and wondering if there's a design pattern
that suits my needs.

I need to implement business logic with a lot of rules and wondering if
there's a design pattern that suits my needs? I'd like it to be flexible to
changes, additions and deletions.

Example:

A person is registered:

If male
- If older than 30
-- Has children
-- Has no children
--- More than two children
-- Is blue eyed
If female
- If older than 30
-- Has children
-- Has no children
-- Likes pizza
 
Hi

I couldn't find a newsgroup discussing software architecure so now I'm
trying my luck here. Please redirect me if there's a newsgroup about
architecture
:-)

I've got the following scenario and wondering if there's a design
pattern that suits my needs.

I need to implement business logic with a lot of rules and wondering
if there's a design pattern that suits my needs? I'd like it to be
flexible to changes, additions and deletions.

Example:

A person is registered:

If male
- If older than 30
-- Has children
-- Has no children
--- More than two children
-- Is blue eyed
If female
- If older than 30
-- Has children
-- Has no children
-- Likes pizza
Click to expand...

It depends on what your goal is:

If you are talking about an object that adds extra attributes
(properties), you can use a decorator pattern. This is more focused on
the state of the object.

If you are talking more about the workflow different users go through,
perhaps a strategy pattern. This is more behavior focused.

Peace and Grace,

--
Gregory A. Beamer
MVP; MCP: +I, SE, SD, DBA

Twitter: @gbworld
Blog: http://gregorybeamer.spaces.live.com

My vacation and childhood cancer awareness site:
http://www.crazycancertour.com

*******************************************
| Think outside the box! |
*******************************************
 
Smith said:
Hi

I couldn't find a newsgroup discussing software architecure so now I'm
trying
my luck here. Please redirect me if there's a newsgroup about architecture
:-)

I've got the following scenario and wondering if there's a design pattern
that suits my needs.

I need to implement business logic with a lot of rules and wondering if
there's a design pattern that suits my needs? I'd like it to be flexible
to
changes, additions and deletions.
Click to expand...

You may want to look into Broken Rules and validation of a Business Object
that is using a Broken Rules validation pattern. You add new validation
rules or remove them out of the Business Object as needed.

http://madskristensen.net/post/Add-validation-to-business-objects.aspx


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Smith said:
I need to implement business logic with a lot of rules and wondering if
there's a design pattern that suits my needs? I'd like it to be flexible to
changes, additions and deletions.

Example:

A person is registered:

If male
- If older than 30
-- Has children
-- Has no children
--- More than two children
-- Is blue eyed
If female
- If older than 30
-- Has children
-- Has no children
-- Likes pizza
Click to expand...

If you want a pattern, which extract these condition chain from
your code, I suggest to define for each end point of such a chain
a criteria name. For example: male->children->.. ==> isCategoryXY
to categorize each person on which then want to execute an action.

I'd try a functor pattern. Encapsulate your function in an object.
As good example have a look in the commons collection project of
the Java apache foundation (language shouldn't be the problem here).

Here is a good example in using such a pattern:

http://onjava.com/pub/a/onjava/2004/12/22/jakarta-gems-1.html?page=2

Implement for each criteria the Predicate interface, signature like

public boolean evaluate(object o);

which code evaluates if the criteria is met. Next, you implement
an "executable" Closure interface with signature

public void execute(object o);

which code executes a closure on the object. You only have to marry
predicate and closure. Map each predicate to its closure:

HashMap predicateMap = new HashMap();
// predicateMap.put(isCategoryXY, doActionOn);

After that you can iterate over the Map with respect to the persons

,-------------------

foreach (Person person in persons)
{
foreach (Predicate predicate in predicateMap.Keys)
{
if (predicate.evaluate(person))
{
predicateMap[predicate].execute(person);
}
}
}

`--------------------

Consider, where to define the Predicates and the Closures. You could
do it probably generic (if there are not only Persons) and define the
Predicates and Closures as a partial class.

Please understand my posting only as an idea and not as a solution.
I didn't try it, yet. Maybe that's a wrong start (could be discussed
here). I just read the above article today and thought it could be
useful for your problem. Sorry, if I might got your questions wrong.

Best

Henning
 
Factory, Strategy and composite patterns will do exactly that. Just a non
working example below should giveyou an idea. This can be interspersed with
factory patterns to load rules dynamicaly/ initially based on sex.


interface IRegistrationRule
{
bool Register(Person person);
}

class AbstractRegistrationRule
{
bool Register(Person person);
}

class ChildrenRegistrationRule : AbstractRegistrationRule
{
bool Register(Person person)
{
Rule..................
}
}

class NoChildrenRegistrationRule : AbstractRegistrationRule
{
bool Register(Person person)
{
Rule..................
}
}

class FoodLikesRegistrationRule : AbstractRegistrationRule
{
bool Register(Person person)
{
Rule..................
}
}


class FoodDisLikesRegistrationRule : AbstractRegistrationRule
{
bool Register(Person person)
{
Rule..................
}
}

abstract class CompositeRegistrationRule: AbstractRegistrationRule
{
IList<IRegistrationRule> rules = new List<IRegistrationRule>;
bool Register(Person person);
}

class MaleRegistrationRule:CompositeRegistrationRule
{


}


class FeMaleRegistrationRule:CompositeRegistrationRule
{
public FeMaleRegistrationRule()
{
rules.Add (new FoodDisLikesRegistrationRule ());
rules.Add (new ChildrenRegistrationRule ());
}

bool Register(Person)
{

bool register = true;
foreach(IregistrationRule rule in rules)
{
register = rule.register(person)
if (register == false)
{
break;
}
}
return register;
}
}
 
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