With ever-growing software occasionally developers will find themselves amid a befuddlement built on complicated and poorly organized conditional logic. Chaos such as this is nearly unmaintainable, even by the original developer. A rules engine allows you to simplify that logic and provide more self-documenting, maintainable code. This explores the use case for a Rules Engines and highlights the existing PHP Rules Engine, Ruler. Talk given to Nashville PHP Meetup 09/09/2014

1. Them’s the Rules
by
Micah Breedlove
Using a Rules Engine to Wrangle
Complexity

2. PHP Dev since ‘98
Symfony Evangelist
@druid628
http://micah.breedlove.in/
Sr. Developer / Team Lead @ iostudio
Who is this guy?

3. Rules Engines
Drools
Open Rules
Jess
Ruler (PHP)

4. Ruler
Written by Justin Hileman(BobTheCow)
GitHub: https://github.com/bobthecow/Ruler
Packagist: ruler/ruler

5. Some definitions

6. Conditional Logic
“hypothetical logic (of a proposition) consisting
of two component propositions... so that the
proposition is false only when the antecedent is
true and the consequent false.”
How we handle the unknown.

7. Rules Engines
“A business rules engine is a software system
that executes one or more business rules in a
runtime production environment.”
“An added layer of complexity to carry out,
often complicated, business logic of the
application”
in other words...

8. Business Logic?
Company policies
Legal Regulations

9. Examples
Discounts on products purchased
Combination of products
Subscribed services
Additional Fees
Geographical assessment
Risk assessment

10. What is wrong with this?
if ( $obj->getName() == ‘abc’) { } elseif ($obj->getName() == ‘def’) {
} elseif ($obj->getName() == ‘ghi’) { } elseif ($obj->getName() == ‘jkl’ ) {
} elseif ($obj->getName() == ‘mno’ ) {
} elseif ($obj->getName() == ‘pqr’ && $obj->getClient()->getCategory() !==
‘hotChkn’) {
}elseif ($obj->getName() == ‘Hg(CNO)2’ && $obj->getClientKey() == ‘tuco’){
}elseif ($obj->getName() == ‘blueSky’ && $obj->getClientKey() ==
‘losPollosHermanos’) {
} elseif ($obj->getName() == ‘blueSky’ && $obj->getClientKey() ==
‘heisenberg’){}

11. ...

12. Should be kept trimmed,
maintained and under control
Or else...
Pandemonium Ensues
Conditional statements are like Kudzu

13. Fixable?
Something to …
Abstractly handle multiple conditions
With
Minimal conditional logic
and is
Reusable

14. Simplifies a block into a generic block
Support more than a simple/singular condition
Abstraction

15. Minimize Conditional Logic
Drop the ever-building conditionals
Replace with smaller defined block

16. Reusability
Ability to support all existing conditions
Individual rules can be evaluated in other
RuleSets

17. The saga begins…
if ($bond->getClient()== ‘client1’ && $event->getName() == ‘bond.create’) {
$this->calculateClient1BondAdjustments($bond);
} elseif ($bond->getClient() == ‘client1’ && $event->getName() == ‘payment.made’) {
$this->calculateClient1Payment($bond, $payment);
} elseif ($bond->getClient() == ‘client2’ && $event->getName() == ‘bond.create’) {
$this->calculateClient2BondAdjustments($bond);
} elseif ($bond->getClient() == ‘client3’ && $event->getName() == ‘bond.create’) {
$this->calculateClient3BondAdjustments($bond);
} ...

18. What We Need
If a Bond is made in Collegedale
A $25 fee should be assessed

19. $rule = $ruleFactory->getBondRules();
$clientRule = [
‘district’ => ‘collegedale’,
‘district_fee’ => ‘25’,
‘fee_adjustment’ => ‘+’
];
$context = new Context([
‘bond_district’ => $bond->getDistrict(),
‘district’ => $clientRule[‘district’],
‘district_fee’ => $clientRule[‘district_fee’],
‘fee_adjustment’ => $clientRule[‘’fee_adjustment’]
]);
$rule->execute($context);
Rule Elements

20. Ruler - Elements of the Equation
3 Parts
Context
Rule
Execution/Evaluation

21. Context - All Applicable Data
Variable Data:
‘bond_district’ => ‘collegedale’,
Control Data:
‘district’ => ‘collegedale’,
‘district_fee’ => ‘25’,
‘fee_adjustment’ => ‘+’
Variable Data
Request
User Specific
(includes session)
Control Data
Specific to the Rule

22. Rule
$rule = $rb->create(
$rb['bond_district']->EqualTo($rb['district'])
);
How the Context Stacks Up
How to evaluate the data
What to evaluate
Variable Data:
‘bond_district’ => ‘collegedale’,
Control Data:
‘district’ => ‘collegedale’,
‘district_fee’ => ‘25’,
‘fee_adjustment’ => ‘+’

23. Rule (cont.)
Compound Rules
$rule = $rb->create(
$rb->LogicalAnd(
$rb['bond_district']->EqualTo($rb['district']),
$rb['bond_amount']->GreaterThan('20000')
)
);

24. Evaluation/Execution
Evaluate - (boolean) Did it meet the condition?
Execution - (void) If it’s true do something

25. Evaluation Example
Rule:
$rule = $rb->create(
$rb['bond_district']->EqualTo($rb['district'])
);
$status = $rule->evaluate($context);
echo $status; // true
Control Data:
‘district’ =>
‘collegedale’,
‘district_fee’ => ‘25’,
‘fee_adjustment’ => ‘+’
Variable Data:
‘bond_district’ => ‘collegedale’

26. Execution Example
$rule->execute($context);
// output: An additional mileage fee will be charged.
Control Data:
‘district’ =>
‘collegedale’,
‘district_fee’ => ‘25’,
‘fee_adjustment’ => ‘+’
Variable Data:
‘bond_district’ => ‘collegedale’
Rule:
$rule = $rb->create(
$rb['bond_district']->EqualTo($rb['district']),
function() {
echo 'An additional mileage fee will be charged.';
}
);

27. if ($bond->getClient()== ‘client1’ && $event->getName() == ‘bond.create’) {
$this->calculateClient1BondAdjustments($bond);
} elseif ($bond->getClient() == ‘client1’ && $event->getName() == ‘payment.made’) {
$this->calculateClient1Payment($bond, $payment);
} elseif ($bond->getClient() == ‘client2’ && $event->getName() == ‘bond.create’) {
$this->calculateClient2BondAdjustments($bond);
} elseif ($bond->getClient() == ‘client3’ && $event->getName() == ‘bond.create’) {
$this->calculateClient3BondAdjustments($bond);
} ...
Finally this…

28. ...becomes this
$ruleObject = $rulesRepo->get($event->getName()); // assume bond.create
$context = $ruleObject->getContext();
$context[‘bond’] = $bond;
$rule = $ruleObject->getRule();
$rule->execute($context); // one rule to rule them all

29. Questions?

30. Demo Time

31. Thanks!

32. Slides: http://sthen.es/mqh4ub20

33. citations
Jesse (Breaking Bad) - http://replygif.net/i/1323.gif
Kudzu - http://2.bp.blogspot.com/_RTswKzWDHeM/SE198zJTgzI/AAAAAAAAA80/ZKj4haQbiSE/s320/kudzu+house.jpg
MC Hammer - http://24.media.tumblr.com/26d1484f43ff55401f8ead9d03432bb9/tumblr_moctg0LbmC1sn8pc2o1_400.gif