Alice wants to create two collections in MongoDB called the unitEnrolment collection and
the student collection. The relationship between the two collections is one-to-many. One
document in the unitEnrolment collection has many related documents in the student collection.
She wrote the following two MongoDB shell commands to populate the database:
db.unitEnrolment.insertOne({
"_id":1, "code":"FIT5148", "students":[1,2,3,4,5]
})

db.student.insertMany([
{"_id":1,"name":"Alita"},
{"_id":4,"name":"Nick"},
{"_id":5,"name":"Tom"}
])
Alice’s aggregation pipeline code produces the following output:

{"_id" : 1, "students" : 1, "details" : [{ "_id" : 1, "name" : "Alita" }]}
{"_id" : 1, "students" : 2, "details" : [ ] }
{"_id" : 1, "students" : 3, "details" : [ ] }
{"_id" : 1, "students" : 4, "details" : [ { "_id" : 4, "name" : "Nick" } ] }
{"_id" : 1, "students" : 5, "details" : [ { "_id" : 5, "name" : "Tom" } ] }

Which of the following aggregation query will produce the above output?

Question

Alice wants to create two collections in MongoDB called the  unitEnrolment  collection and 
 the  student  collection. The relationship between the two collections is one-to-many. One 
 document in the  unitEnrolment  collection has many related documents in the  student  collection. 
 She wrote the following two MongoDB shell commands to populate the database: 
 db.unitEnrolment.insertOne({ 
 "_id":1, "code":"FIT5148", "students":[1,2,3,4,5] 
 }) 
 
 db.student.insertMany([ 
 {"_id":1,"name":"Alita"}, 
 {"_id":4,"name":"Nick"}, 
 {"_id":5,"name":"Tom"} 
 ]) 
 Alice’s aggregation pipeline code produces the following output: 
  
 {"_id" : 1, "students" : 1, "details" : [{ "_id" : 1, "name" : "Alita" }]} 
 {"_id" : 1, "students" : 2, "details" : [ ] } 
 {"_id" : 1, "students" : 3, "details" : [ ] } 
 {"_id" : 1, "students" : 4, "details" : [ { "_id" : 4, "name" : "Nick" } ] } 
 {"_id" : 1, "students" : 5, "details" : [ { "_id" : 5, "name" : "Tom" } ] } 
  
 Which of the following aggregation query will produce the above output?

Answer

db.student.aggregate([ 
           {$unwind:"$students"}, 
           {$lookup:  
                {from: " unitEnrolment ",      
                     localField: "students", 
                     foreignField: "_id",      
                     as: "details"}      
                } 
 ])

Answer

db.student.aggregate([ 
           {$lookup:  
                {from: " unitEnrolment ",      
                     localField: "students", 
                     foreignField: "_id",      
                     as: "details"}      
                } 
 ])

Answer

db.unitEnrolment.aggregate([ 
           {$unwind:"$students"}, 
           {$lookup:  
                {from: "student",      
                     localField: "students", 
                     foreignField: "_id",      
                     as: "details"}      
                } 
 ])

Answer

db.unitEnrolment.aggregate([ 
           {$unwind:"$students"}, 
           {$lookup:  
                {from: "unitEnrolment",      
                     localField: "students", 
                     foreignField: "_id",      
                     as: "details"}      
                } 
 ])

Crowdly

Alice wants to create two collections in MongoDB called the unitEnrolment coll...

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