我正在嘗試制作一個使用 2 個資料庫來生成罰款的 API。這是代碼：
router.get("/generateFine/:bookingID/:currDate", function (req, res, next) {
var currDate,
returnDate,
fine,
totalFine = 0;
Booking.findOne({ _id: req.params.bookingID }).then(function (booking) {
Car.findOne({ _id: booking.carID }).then(function (car) {
currDate = Date.parse(req.params.currDate) / 1000 / 3600 / 24;
returnDate = Date.parse(booking.bookingDates[1]) / 1000 / 3600 / 24;
fine = car.fine;
if (currDate > returnDate) {
totalFine = fine * (currDate - returnDate);
}
console.log(totalFine);
// res.send(totalFine);
});
console.log("totalFine is " totalFine);
// res.send(totalFine);
});
});
以下是代碼中使用的兩個 Schema： Booking Schema：
{
"_id" : ObjectId("621bf46602edf12942f0d5c9"),
"carID" : "621b87af70c150da70b1dabf",
"bookingDates" : [
"2022-03-05",
"2022-03-06"
],
}
汽車架構：
{
"_id" : ObjectId("621b87af70c150da70b1dabf"),
"name" : "Toyota",
"rate" : 60,
"fine" : 10,
"datesBooked" : [
{
"from" : "2022-03-05",
"to" : "2022-03-06"
},
{
"from" : "2022-03-07",
"to" : "2022-03-08"
},
{
"from" : "2022-03-09",
"to" : "2022-03-10"
}
],
"__v" : 0
}
我想將生成的罰款返還給用戶。當我嘗試發送結果時，它會引發錯誤。第一個控制臺日志列印正確的結果，但第二個控制臺日志列印 0。另外，我怎樣才能發送結果而不出錯。已經謝謝了！
uj5u.com熱心網友回復：
您可以使用$lookup聚合管道階段來包含在該carID欄位上匹配的汽車檔案，創建額外的計算欄位，以幫助您在使用必要的聚合運算子時獲得總罰款。
本質上，您需要運行以下聚合管道：
const mongoose = require('mongoose');
router.get('/generateFine/:bookingID/:currDate', async function (req, res, next) {
const currDate = new Date(req.params.currDate);
const [{ totalFine }] = await Booking.aggregate([
{ $match: { _id: mongoose.Types.ObjectId(req.params.bookingID) }},
{ $lookup: {
from: 'cars', // or from: Car.collection.name
let: { carId: { $toObjectId: '$carID' } }, // convert the carID string field to ObjectId for the match to work correctly
pipeline: [
{ $match: {
$expr: { $eq: [ '$_id', '$$carId' ] }
} }
],
as: 'car'
} },
{ $addFields: {
car: { $arrayElemAt: ['$car', 0 ] }, // get the car document from the array returned above
returnDate: {
$toDate: { $arrayElemAt: ['$bookingDates', 1 ]}
}
} },
// compute the overdue days
{ $addFields: {
overdueDays: {
$trunc: {
$ceil: {
$abs: {
$sum: {
$divide: [
{ $subtract: [currDate, '$returnDate'] },
60 * 1000 * 60 * 24
]
}
}
}
}
}
} },
{ $project: { // project a new field
totalFine: {
$cond: [
{ $gt: [currDate, '$returnDate'] }, // IF current date is greater than return date
{ $multiply: ['$car.fine', '$overdueDays'] }, // THEN multiply car fine with the overdue days
0 // ELSE total fine is 0
]
}
} }
]).exec();
console.log("totalFine is " totalFine);
// res.send(totalFine);
});
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