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);
})

...

CodePudding user response：

$match and $group must be in different pipeline operations

const obj = await this.aggragate([
  { $match: { bootcamp: bootcampId } },
  {
    $group: {
      _id: '$bootcamp',
      averageCost: { $avg: '$tuition' },
    },
  },
]).toArray()