add fact-comparison example

Author: Cache Hamm

examples/08-fact-comparison.js

@@ -0,0 +1,138 @@
+'use strict'
+
+/*
+ * This is a basic example demonstrating a condition that compares two facts
+ *
+ * Usage:
+ * node ./examples/08-fact-comparison.js
+ *
+ * For detailed output:
+ * DEBUG=json-rules-engine node ./examples/08-fact-comparison.js
+ */
+
+require('colors')
+let Engine = require('../dist').Engine
+
+/**
+ * Setup a new engine
+ */
+let engine = new Engine()
+
+/**
+ * Rule for determining if account has enough money to purchase a $50 gift card product
+ *
+ * customerAccount (in euros) >= $50 gift card
+ */
+let rule = {
+ conditions: {
+ all: [{
+ // extract 'balance' from the 'customer' account type
+ fact: 'account',
+ path: '.balance',
+ params: {
+ accountType: 'customer'
+ },
+
+ operator: 'greaterThanInclusive', // >=
+
+ // "value" in this instance is an object containing a fact definition
+ // fact helpers "path" and "params" are supported here as well
+ value: {
+ fact: 'product',
+ path: '.price',
+ params: {
+ productId: 'giftCard'
+ }
+ }
+ }]
+ },
+ event: { type: 'customer-can-afford-gift-card' }
+}
+engine.addRule(rule)
+
+engine.addFact('account', (params, almanac) => {
+ // get account list
+ return almanac.factValue('accounts')
+ .then(accounts => {
+ // use "params" to filter down to the type specified, in this case the "customer" account
+ let customerAccount = accounts.filter(account => account.type === params.accountType)
+ // return the customerAccount object, which "path" will use to pull the "balance" property
+ return customerAccount[0]
+ })
+})
+
+engine.addFact('product', (params, almanac) => {
+ // get product list
+ return almanac.factValue('products')
+ .then(products => {
+ // use "params" to filter down to the product specified, in this case the "giftCard" product
+ let product = products.filter(product => product.productId === params.productId)
+ // return the product object, which "path" will use to pull the "price" property
+ return product[0]
+ })
+})
+
+/**
+ * Register listeners with the engine for rule success and failure
+ */
+let facts
+engine
+ .on('success', (event, almanac) => {
+ console.log(facts.userId + ' DID '.green + 'meet conditions for the ' + event.type.underline + ' rule.')
+ })
+ .on('failure', rule => {
+ console.log(facts.userId + ' did ' + 'NOT'.red + ' meet conditions for the ' + rule.event.type.underline + ' rule.')
+ })
+
+// define fact(s) known at runtime
+let productList = {
+ products: [
+ {
+ productId: 'giftCard',
+ price: 50
+ }, {
+ productId: 'widget',
+ price: 45
+ }, {
+ productId: 'widget-plus',
+ price: 800
+ }
+ ]
+}
+
+let userFacts = {
+ userId: 'washington',
+ accounts: [{
+ type: 'customer',
+ balance: 500
+ }, {
+ type: 'partner',
+ balance: 0
+ }]
+}
+
+// compile facts to be fed to the engine
+facts = Object.assign({}, userFacts, productList)
+
+engine
+ .run(facts) // first run, user can afford a gift card
+ .then(() => {
+ // second run; a user that cannot afford a gift card
+ userFacts = {
+ userId: 'jefferson',
+ accounts: [{
+ type: 'customer',
+ balance: 30
+ }]
+ }
+ facts = Object.assign({}, userFacts, productList)
+ return engine.run(facts)
+ })
+ .catch(console.log)
+
+/*
+ * OUTPUT:
+ *
+ * washington DID meet conditions for the customer-can-afford-gift-card rule.
+ * jefferson did NOT meet conditions for the customer-can-afford-gift-card rule.
+ */