json-rules-engine almanac 简单说明

almanac 实际上就是一个上下文对象，可以对于engine 中依赖的一些fact 进行计算处理，同时可以方便的进行动态fact维护，同时还会复用以前的一些计算fact

官方参考使用

官方有一个比较完整的介绍例子

/*
 * Base fact for retrieving account data information.
 * Engine will automatically cache results by accountId
 */
let accountInformation = new Fact('account-information', function(params, almanac) {
   return request
      .get({ url: `http://my-service/account/${params.accountId}`)
      .then(function (response) {
         return response.data
      })
})

/*
 * Calls the account-information fact with the appropriate accountId.
 * Receives a promise w/results unique to the accountId
 */
let isFundedAccount = new Fact('is-funded-account', function(params, almanac) {
   return almanac.factValue('account-information', { accountId: params.accountId }).then(info => {
     return info.funded === true
   })
})

/*
 * Calls the account-information fact with the appropriate accountId.
 * Receives a promise w/results unique to the accountId
 */
let accountBalance = new Fact('account-balance', function(params, almanac) {
   return almanac.factValue('account-information', { accountId: params.accountId }).then(info => {
     return info.balance
   })
})

/*
 * Add the facts the the engine
 */
engine.addFact(accountInformation)
engine.addFact(isFundedAccount)
engine.addFact(accountBalance)

/*
 * Run the engine.
 * account-information will be loaded ONCE for the account, regardless of how many
 * times is-funded-account or account-balance are mentioned in the rules
 */

engine.run({ accountId: 1 })

almanac 使用场景

获取fact，动态设置fact基于event 获取fact 数据信息，进行fact 依赖处理

参考资料

https://github.com/CacheControl/json-rules-engine/blob/master/docs/almanac.md

https://github.com/CacheControl/json-rules-engine/blob/master/examples/04-fact-dependency.js