得到這個錯誤：引數必須是聚合管道運算子，這是將訓練營作為 objectId 的課程“架構”。
const CourseSchema = new mongoose.Schema({
bootcamp: {
type: mongoose.Schema.ObjectId,
ref: 'Bootcamp',
required: true
}
});
聚合：
//static method to get avg of course tuitions
CourseSchema.statics.getAverageCost = async function (bootcampId) {
console.log('calculating avg cost... with bootcampId:' bootcampId);
const obj = await this.aggragate([{
$match: { bootcamp: bootcampId },
$group: {
_id: '$bootcamp',
averageCost: { $avg: '$tuition' }
}
}]);
console.log(obj);
}
在保存或洗掉之前呼叫聚合：
...
// Call getAvarageCost after save
CourseSchema.post('save', function () {
this.constructor.getAverageCost(this.bootcamp);
})
// Call getAvarageCost before remove
CourseSchema.post('remove', function () {
this.constructor.getAverageCost(this.bootcamp);
})
...
uj5u.com熱心網友回復：
$match 和 $group 必須在不同的管道操作中
const cursor = this.aggregate([
{ $match: { bootcamp: bootcampId } },
{
$group: {
_id: '$bootcamp',
averageCost: { $avg: '$tuition' },
},
},
])
console.log(await cursor.toArray())
轉載請註明出處，本文鏈接：https://www.uj5u.com/shujuku/371153.html
標籤：javascript MongoDB 猫鼬 总计的 聚合