Javascript中的INNER JOIN

Question

const products = [{

    id: 5,

    productName: "Logitech Mouse",

    unitprice: 35

  },

  {

    id: 6,

    productName: "Logitech Keyboard",

    unitprice: 40

  }

];

const cart = [{

    id: 101,

    userId: 3,

    productId: 5,

    quantity: 2

  },

  {

    id: 102,

    userId: 3,

    productId: 6,

    quantity: 1

  }

];

Answer 1

我会要求您在寻求帮助之前先尝试一下自己，以便以最好的方式从社区获得帮助。您可以尝试使用和.map()解构赋值：find()const products = [{    id: 5,    productName: "Logitech Mouse",    unitprice: 35  },  {    id: 6,    productName: "Logitech Keyboard",    unitprice: 40  }];const cart = [{    id: 101,    userId: 3,    productId: 5,    quantity: 2  },  {    id: 102,    userId: 3,    productId: 6,    quantity: 1  }];var res = products.map(({id,...rest}) => {  var cartObj = cart.find(c => c.productId == id);  rest.quantity = (cartObj != undefined && 'quantity' in  cartObj) ? cartObj.quantity : 'N/A';  return rest;});console.log(res);

Answer 2

您可以采用更类似于 SQL 的方法为产品创建哈希表，并使用哈希表中对象的所需属性映射购物车，以及quantity结果，您将获得带有产品名称、单价和数量的新对象。const    select = (keys, object) => Object.fromEntries(keys.map(k => [k, object[k]])),    products = [{ id: 5, productName: "Logitech Mouse", unitprice: 35 }, { id: 6, productName: "Logitech Keyboard", unitprice: 40 }],    cart = [{ id: 101, userId: 3, productId: 5, quantity: 2 }, { id: 102, userId: 3, productId: 6, quantity: 1 }],    productsMap = products.reduce((r, o) => (r[o.id] = o, r), {}),    result = cart.map(({ productId, quantity }) => ({         ...select(['productName', 'unitprice'], productsMap[productId]),        quantity    }));    console.log(result);.as-console-wrapper { max-height: 100% !important; top: 0; }