got this error: arguments must be aggregate pipeline operators this is the course 'Schema" that got bootcamp as objectId.
const CourseSchema = new mongoose.Schema({
bootcamp: {
type: mongoose.Schema.ObjectId,
ref: 'Bootcamp',
required: true
}
});
the aggregation :
//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);
}
calling for the aggregation before saving or removing:
...
// 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);
})
...
$match and $group must be in different pipeline operations
const cursor = this.aggregate([
{ $match: { bootcamp: bootcampId } },
{
$group: {
_id: '$bootcamp',
averageCost: { $avg: '$tuition' },
},
},
])
console.log(await cursor.toArray())