代码之家 › 专栏 › 技术社区 › Tomasz Lempart

使用Ramda将对象数组与父属性映射在一起

ramda.js functional-programming javascript

Tomasz Lempart · 技术社区 · 3 年前

我是函数式编程和ramda的新手。我有一个案例,用命令式方法很容易解决,但我很难用声明式方法解决。我有以下结构,描述了多个库存。

inventories = [
  {
    id: 'Berlin',
    products: [{ sku: '123', amount: 99 }],
  },
  {
    id: 'Paris',
    products: [
      { sku: '456', amount: 3 },
      { sku: '789', amount: 777 },
    ],
  },
]

我想做的是将其转换为一个简单的产品列表,其中包含其他信息,如 inventoryId , inventoryIndex ,以及 productIndex .

products = [
  { inventoryId: 'Berlin', inventoryIndex: 1, sku: '123', amount: 99, productIndex: 1 },
  { inventoryId: 'Paris', inventoryIndex: 2, sku: '456', amount: 3, productIndex: 1 },
  { inventoryId: 'Paris', inventoryIndex: 2, sku: '789', amount: 777, productIndex: 2 },
]

正如我之前所写的,以命令式的方式做到这一点不是问题。

function enrichProductsWithInventoryId(inventories) {
  const products = []
  for (const [inventoryIndex, inventory] of inventories.entries()) {
    for (const [productIndex, product] of inventory.products.entries()) {
      product.inventoryId = inventory.id
      product.inventoryIndex = inventoryIndex + 1
      product.productIndex = productIndex + 1
      products.push(product)
    }
  }

  return products
}

问题是当我试图用ramda解决这个问题时。我不知道如何进入 库存Id ,同时绘制产品图。如果能看到一段使用ramda编写的代码,那就太好了,它的功能与上面的代码相同。

干杯, 托马什

0 回复 | 直到 3 年前

Aadit M Shah 3 年前

您可以使用以下工具轻松完成此操作 flatMap .

const inventories = [
    {
        id: "Berlin",
        products: [{ sku: "123", amount: 99 }]
    },
    {
        id: "Paris",
        products: [
            { sku: "456", amount: 3 },
            { sku: "789", amount: 777 }
        ]
    }
];

const products = inventories.flatMap((inventory, inventoryIndex) =>
    inventory.products.map((product, productIndex) => ({
        inventoryId: inventory.id,
        inventoryIndex: inventoryIndex + 1,
        sku: product.sku,
        amount: product.amount,
        productIndex: productIndex + 1
    })));

console.log(products);

请注意 平面地图 被称为 chain 在拉姆达,但你需要 addIndex 到它。

const inventories = [
    {
        id: "Berlin",
        products: [{ sku: "123", amount: 99 }]
    },
    {
        id: "Paris",
        products: [
            { sku: "456", amount: 3 },
            { sku: "789", amount: 777 }
        ]
    }
];

const chainIndexed = R.addIndex(R.chain);
const mapIndexed = R.addIndex(R.map);

const products = chainIndexed((inventory, inventoryIndex) =>
    mapIndexed((product, productIndex) => ({
        inventoryId: inventory.id,
        inventoryIndex: inventoryIndex + 1,
        sku: product.sku,
        amount: product.amount,
        productIndex: productIndex + 1
    }), inventory.products), inventories);

console.log(products);

<script src="https://unpkg.com/ramda@0.27.1/dist/ramda.min.js"></script>

Scott Sauyet 3 年前

我可能会以与Aadit建议类似的方式进行此操作,尽管我会稍微改变一下框架,并使用参数解构

const convert = (inventories) =>
  inventories .flatMap (({id: inventoryId, products}, i, _, inventoryIndex = i + 1) =>
    products.map (
      ({sku, amount}, i, _, productIndex = i + 1) => 
        ({inventoryId, inventoryIndex, sku, amount, productIndex})
    )
  )

const inventories = [{id: "Berlin", products: [{sku: "123", amount: 99}]}, {id: "Paris", products: [{sku: "456", amount: 3}, {sku: "789", amount: 777}]}]

console .log (convert (inventories));

.as-console-wrapper {max-height: 100% !important; top: 0}

但是,如果你想把它分解成更小的组成部分,Ramda可以帮助你把它们写下来,并把它们粘在一起。如果我们试图描述我们正在做的事情,我们可能会把它看作四个步骤。我们重命名 id 字段到 inventoryId ,我们为库存添加一个运行指数,并为每组添加单独的指数 products ,我们通过提升 产品 数组与其父数组合并。

所有这些都是潜在的可重用转换。如果我们愿意,我们可以为这些函数分解出单独的辅助函数,然后使用Ramda将它们组合成一个函数。它可能看起来像这样:

const {pipe, toPairs, map, fromPairs, addIndex, chain, merge, evolve} = R

const mapKeys = (cfg) => pipe (
  toPairs,
  map (([k, v]) => [cfg [k] || k, v]),
  fromPairs
)
 
const addOrdinals = (name) => 
  addIndex (map) ((x, i) => ({... x, [name]: i + 1 }))

const promote = (name) => 
  chain (({[name]: children, ...rest}) => map (merge(rest), children))

const transform = pipe (
  map (mapKeys ({id: 'inventoryId'})),
  addOrdinals ('inventoryIndex'),
  map (evolve ({products: addOrdinals ('productIndex')})),
  promote ('products')
)

const inventories = [{id: "Berlin", products: [{sku: "123", amount: 99}]}, {id: "Paris", products: [{sku: "456", amount: 3}, {sku: "789", amount: 777}]}]

console .log (transform (inventories))

.as控制台包装器{最大高度:100%!重要;顶部:0}

<script src="//cdnjs.cloudflare.com/ajax/libs/ramda/0.27.1/ramda.min.js"></script>

这涉及更多的代码,但我们所做的是创建一些有用的小函数,并通过编写对这些小函数的调用来使我们的主函数更具声明性。这可能值得也可能不值得在你的项目中做,但肯定值得考虑。