rules-when

Simple When Rule Construction

BizRez When Rules

A simple way to dynamically create when rules - A great example how to use the new Function instead of the 'evil' eval.

Intro

Simplicity is elegance.

What we need is a descriptive way to tag Biz(i)ness Rules and catalog, inventory, usage, and change rules dynamically. Javascript provides a simple way of dynamically creating functions on the fly.

Prime directives, and ables ...

• Easy to understand the code
• Thin
• Self-documenting
• Pattern - not an enforcement
• Crazy fast
• Secure from XXS

Dependencies

• Mocha.js for for test infecting the code (good infection)

A few Use Cases for Usage

• Validations
• Calculations
• Automated business rules - decision engine
• Home security, sprinkler systems, and darn maybe your car...

Benefits

• Repository of rules
• Traceability
• Modify the rule not the code
• Dynamic changeability - conditions change so do the execution
• Easy to understand and modify
• Extensible
• Maintainable
• Reusable
• Chainable
• Micro foot print and scalable

Example Setup

//Example Setup

var when = {

    isPerson: "return object.isPerson === true //Comment - Yes you can",
    hasLicense: "return object.license === true //Comment",
    isPersonAndHasLicense: "return when['isPerson'](object) && when['hasLicense'](object)",
    payTax: "return object.payTax === true",
    doHula: "return when['isPerson'](object) && when['hasLicense'](object) && when['payTax'](object)"

}

var calculate = {

    adder: "return object.a + object.b //Comment",
    calculateTax: "return object.amount * 1.8",
    addTax: "if (when['payTax'](object)) {return calculate['calculateTax'](object)}; return 0",
    mutate: "object.tada = 'hello Moto'; return true"

}

//Describe Decision Table
var decisionTable = {

    calcNumber: [["return when['isPerson'](object)", "return calculate['adder'](object)", "return true"],
        ["return when['isPerson'](object)", "return calculate['calculateTax'](object)", "return true"],
        ["return when['isPerson'](object)", "return calculate['calculateTax'](object)", "return true"]
    ]

}

---

image 1

Notice: functions stored as strings. These strings will be translated via the new Function operation


Translate value into functions

        //Create When Condtion functions

        function loadwhenConditions(when) {

            //Convert key[value] into real functions
            for (var key in when) {
                when[key] = new Function('object', 'when', 'calculate', when[key]);
            }

        }

        //Create Calculation functions
        function loadCalcualtions(calculate) {
            //Convert key[value] into real functions
            for (var key in calculate) {
                calculate[key] = new Function('object', 'when', 'calculate', calculate[key]);

            }
        }

Example Run

rules.loadWhenRules(when);
rules.loadCalcualtions(calculate);
rules.loadDecisionTable(decisionTable);

var person = {isPerson: true, license: true, a: 5, b: 10, amount: 500, payTax: true};

console.log("isPerson:" + rules.when('isPerson', person));
console.log("hasLicense:" + rules.when('hasLicense', person));
console.log("adder:" + rules.calculate('adder', person));
console.log("addTax:" + rules.calculate("addTax", person));
console.log("isPersonAndHasLicense:" + rules.when('isPersonAndHasLicense', person));
console.log(person.tada);
console.log("decisiontable result:" + rules.decisionTable('calcNumber', person));
console.log("doHula:" + rules.when('doHula',person));

An alternative using the evil eval()

// From couchDB
var input = {
    id: "tax",
    state: "tx",
    rate: 7.15,
    shows: {
        adder: "function(input) {return input.rate * input.value;}",
        detail: "function(detail){ alert(detail) }"
    }
};

// Construct function with Closure
var fullFunction = "(function () {var counter = 0; return " + input.shows.adder + "})()";

// Construct function
var ad = eval(fullFunction);

var input = {rate:input.rate, value : 10000}
console.log(ad(input));

// "a thought" create JS Objects stringify load into CouchDB

function objToString(obj, ndeep) {
    switch(typeof obj){
        case "string": return '"'+obj+'"';
        case "function": return obj.name || obj.toString();
        case "object":
            var indent = Array(ndeep||1).join('\t'), isArray = Array.isArray(obj);
            return ('{['[+isArray] + Object.keys(obj).map(function(key){
                return '\n\t' + indent +(isArray?'': key + ': ' )+ objToString(obj[key], (ndeep||1)+1);
            }).join(',') + '\n' + indent + '}]'[+isArray]).replace(/[\s\t\n]+(?=(?:[^\'"]*[\'"][^\'"]*[\'"])*[^\'"]*$)/g,'');
        default: return obj.toString();
    }
}

var test = {fx: function(a, b) {return a*b}};
console.log(test.fx(5,5));
console.log(objToString(test));

Mocha Test

mocha ./lib/test

Key: BRE, Decision Table, When, Calculation, BPM Business Process Management