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Retrieving group by result with arrays in MongoDB?
To retrieve group by result with arrays, use aggregate(). We will also use $addToSet operator. It adds a value to an array unless the value is already present, in which case $addToSet does nothing to that array.
Let us create a collection with documents −
> db.demo498.insertOne({id:1,Name:["Chris"]});{
"acknowledged" : true,
"insertedId" : ObjectId("5e86192b987b6e0e9d18f553")
}
> db.demo498.insertOne({id:2,Name:["David"]});{
"acknowledged" : true,
"insertedId" : ObjectId("5e86192d987b6e0e9d18f554")
}
> db.demo498.insertOne({id:3,Name:["Chris"]});{
"acknowledged" : true,
"insertedId" : ObjectId("5e861931987b6e0e9d18f555")
}
> db.demo498.insertOne({id:4,Name:["Bob"]});{
"acknowledged" : true,
"insertedId" : ObjectId("5e861942987b6e0e9d18f556")
}
> db.demo498.insertOne({id:5,Name:["David"]});{
"acknowledged" : true,
"insertedId" : ObjectId("5e861947987b6e0e9d18f557")
}Display all documents from a collection with the help of find() method −
> db.demo498.find();
This will produce the following output −
{ "_id" : ObjectId("5e86192b987b6e0e9d18f553"), "id" : 1, "Name" : [ "Chris" ] }
{ "_id" : ObjectId("5e86192d987b6e0e9d18f554"), "id" : 2, "Name" : [ "David" ] }
{ "_id" : ObjectId("5e861931987b6e0e9d18f555"), "id" : 3, "Name" : [ "Chris" ] }
{ "_id" : ObjectId("5e861942987b6e0e9d18f556"), "id" : 4, "Name" : [ "Bob" ] }
{ "_id" : ObjectId("5e861947987b6e0e9d18f557"), "id" : 5, "Name" : [ "David" ] }Following is the query to retrieve group by result with arrays in MongoDB −
> db.demo498.aggregate([{
... $unwind : "$Name"
... }, {
... $group : {
... _id : $quot;$Name",
... Id : {
... $addToSet : "$id"
... }
... }
... }
... ])This will produce the following output −
{ "_id" : "David", "Id" : [ 5, 2 ] }
{ "_id" : "Bob", "Id" : [ 4 ] }
{ "_id" : "Chris", "Id" : [ 3, 1 ] }
Updated on: 13-May-2020
1K+ Views
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