使用ramda處理的承諾，並等待

Question

我有一段代碼寫的lodash象下面這樣：

const profit = 
    price - 
    _.sumBy(
    await Promise.all(
     map(uOrder => uOrder.invoice, await order.upstreamOrders), 
    ), 
    'amount', 
); 

我想改變它ramda，後夫婦的思考和閱讀一些文件我寫下面的代碼：

const resualt = R.compose(
    R.pick(['amount']), 
    await Promise.all(), 
    R.map(await order.upstreamOrders, uOrder.invoice), 
); 

當然

其錯誤和不工作，但它的第一種方法，我想知道如何處理這樣的使用ramda完美和功能方式的情況。我該如何執行此操作？ 還下令對象是下面的示例的數組：

{ 
"_id" : ObjectId("59dce1f92d57920d3e62bdbc"), 
"updatedAt" : ISODate("2017-10-10T15:06:34.111+0000"), 
"createdAt" : ISODate("2017-10-10T15:06:33.996+0000"), 
"_customer" : ObjectId("59dce1f92d57920d3e62bd44"), 
"_distributor" : ObjectId("59dce1f92d57920d3e62bd39"), 
"status" : "NEW", 
"cart" : [ 
    { 
     "count" : NumberInt(1), 
     "_item" : ObjectId("59dce1f92d57920d3e62bd57"), 
     "_id" : ObjectId("59dce1f92d57920d3e62bdc1") 
    }, 
    { 
     "count" : NumberInt(1), 
     "_item" : ObjectId("59dce1f92d57920d3e62bd5c"), 
     "_id" : ObjectId("59dce1f92d57920d3e62bdc0") 
    }, 
    { 
     "count" : NumberInt(1), 
     "_item" : ObjectId("59dce1f92d57920d3e62bd61"), 
     "_id" : ObjectId("59dce1f92d57920d3e62bdbf") 
    }, 
    { 
     "count" : NumberInt(1), 
     "_item" : ObjectId("59dce1f92d57920d3e62bd66"), 
     "_id" : ObjectId("59dce1f92d57920d3e62bdbe") 
    }, 
    { 
     "count" : NumberInt(1), 
     "_item" : ObjectId("59dce1f92d57920d3e62bd6b"), 
     "_id" : ObjectId("59dce1f92d57920d3e62bdbd") 
    } 
], 
"_upstreamOrders" : [ 
    "4545643499" 
], 
"key" : "4592846350", 
"__v" : NumberInt(1), 
"_invoice" : "0811260909610702" 

}

Answer 1

我覺得這是一個好的開始打破究竟原始功能是做

const profit = 
    price - // subtract the result 
    _.sumBy(
    await Promise.all(
     // Wait for upstreamOrders to resolve, and grab the 'invoice' 
     // key for each 
     map(uOrder => uOrder.invoice, await order.upstreamOrders), 
    ), 
    // calculate the sum of the invoices, based on the 'amount' key 
    'amount', 
); 

隨着該記住我們可以分解這些步驟，並將計算（同步）與數據分開（異步）

Ramda沒有sumBy，因爲我們可以從其他函數中構建它。如果你打破它，我們所做的就是搶invoice，並在兩個不同的地方amount，但我們可以只抓數量的陣列

map(path(['invoice', 'amount'])) 

我們可以丟棄旁邊一個sum和subtract創建一個函數，它是從我們的異步代碼完全獨立

const calculateProfits = (price, orders) => compose(
    subtract(price), 
    sum, 
    map(path(['invoice', 'amount'])), 
)(orders) 

允許我們做一些事情，如：

const profit = calculateProfits(price, await order.upstreamOrders) 

或者，如果calculateProfits是咖喱（我不知道upstreamOrders是如何工作的，難道是返回一個承諾一個getter？）

const getUpstreamOrders = order => order.upstreamOrders 

getUpstreamOrders(order) 
    .then(calculateProfits(price)) 
    .then(profits => { 
    // Do what you want with the profits 
    }) 

最後，在初步嘗試

const result = R.compose(
    R.pick(['amount']), 

    // Promise.all is being called without any arguments 
    // it doesn't really fit within `compose` anyway, but if we were 
    // feeding an array of promises through, we'd want to just 
    // put `Promise.all,` 
    await Promise.all(), 

    // the arguments here should be the other way around, we're 
    // mapping over upstreamOrders, and the data comes last 
    // uOrder isn't available in this scope, previously it was 
    // `uOrder => uOrder.invoice`, 
    // invoking a function and returning the invoice for that order 
    R.map(await order.upstreamOrders, uOrder.invoice), 
);