Using aggregation pipeline to fetch records in MongoDB

MongoDBDatabaseBig Data Analytics

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 }
raja
Updated on 30-Mar-2020 12:43:02

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