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const pipeline = [
{ "$addFields": {"StudentId": "$_id" } },
{"$project":{
"_id":0,
"createdat":0,
"updatedat":0,
"__v":0
}}
]
return students.aggregate(pipeline).toArray()
.then(students => {
console.log(`Successfully grouped purchases for ${students.length} customers.`)
students.forEach(console.log);
return students
})
.catch(err => console.error(`Failed to find documents: ${err}`));*/