More Rules

Add an approval rule, and control order and exceptions with priority, stop and except.

More Rules

One rule is not much of a decision. Let's finish the loan rulebook. Replace models/LoanApproval.bx with this:

class extends="rulebox.models.RuleBook"{

	function defineRules(){
		addRule(
			newRule( "declineLowScores" )
				.withPriority( 20 )
				.when( ( facts ) => facts.creditScore < 580 )
				.then( ( facts, result ) => result.setValue( "DECLINED" ) )
				.stop()
		)

		addRule(
			newRule( "autoApprove" )
				.when( ( facts ) => facts.creditScore >= 680 )
				.except( ( facts ) => facts.requestedAmount > facts.income * 5 )
				.then( ( facts, result ) => result.setValue( "APPROVED" ) )
		)
	}

}

There are three new ideas in there.

withPriority()

Rules run from the highest priority to the lowest. The default is 0. Here declineLowScores has priority 20, so it always goes first. Rules with the same priority run in the order you added them.

Set the priority before you call addRule().

stop()

stop() ends the whole chain once that rule has fired. Once someone is declined, there is no point checking whether to approve them.

except()

except() is the opposite of when(): skip the rule if this is true. Here a good score is approved, except when the amount asked for is more than five times their income.

Run it

Use the default from lesson 3 so there is always an answer:

var decision = getInstance( "LoanApproval" )
	.withDefaultResult( "MANUAL_REVIEW" )
	.run( { creditScore: 720, income: 80000, requestedAmount: 100000 } )
	.getResult()
	.getValue()

Here is what you get for the four applicants from lesson 1. Every income is 80000.

Tip: if a rule has more than one then(), write each action with a { ... } body instead of the short => form. The short form returns its value, and a then() that returns true stops the later ones in that rule.

Try it

Change the approval threshold from 680 to 700 and run the 720 and 690 applicants. The 690 applicant moves from APPROVED to MANUAL_REVIEW. In the next lesson you will see exactly why.

Next: find out which rules ran.