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Using aggregation pipeline to fetch records in MongoDB
The MongoDB aggregation pipeline has stages. Each stage transforms the documents as they pass through the pipeline.
Let us first create a collection with documents −
> db.demo218.insertOne({"Name":"Chris","Branch":"CS",Marks:[65,78,36,90]});
{
"acknowledged" : true,
"insertedId" : ObjectId("5e3e5f4903d395bdc2134712")
}
> db.demo218.insertOne({"Name":"David","Branch":"ME",Marks:[56,45,42,51]});
{
"acknowledged" : true,
"insertedId" : ObjectId("5e3e5f6203d395bdc2134713")
}
> db.demo218.insertOne({"Name":"Chris","Branch":"CS",Marks:[78,65,89]});
{
"acknowledged" : true,
"insertedId" : ObjectId("5e3e5f6c03d395bdc2134714")
}Display all documents from a collection with the help of find() method −
> db.demo218.find();
This will produce the following output −
{ "_id" : ObjectId("5e3e5f4903d395bdc2134712"), "Name" : "Chris", "Branch" : "CS", "Marks" : [ 65, 78, 36, 90 ] }
{ "_id" : ObjectId("5e3e5f6203d395bdc2134713"), "Name" : "David", "Branch" : "ME", "Marks" : [ 56, 45, 42, 51 ] }
{ "_id" : ObjectId("5e3e5f6c03d395bdc2134714"), "Name" : "Chris", "Branch" : "CS", "Marks" : [ 78, 65, 89 ] }Following is the query for aggregation pipeline −
> db.demo218.aggregate([
... { "$unwind": "$Marks" },
... { "$match":
... {
... "Branch": "CS",
... "Marks": { "$gt": 88 }
... }
... },
... { "$group":
... {
... "_id": "$_id",
... "Branch": { "$first": "$Branch" },
... "Marks": { "$first": "$Marks" }
... }
... }
...])This will produce the following output −
{ "_id" : ObjectId("5e3e5f6c03d395bdc2134714"), "Branch" : "CS", "Marks" : 89 }
{ "_id" : ObjectId("5e3e5f4903d395bdc2134712"), "Branch" : "CS", "Marks" : 90 }
Updated on: 30-Mar-2020
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