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Unable to implement $addToSet in MongoDB to fetch values of a single field?
The $addToSet operator adds 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.demo533.insertOne({"ProjectName":"Online Hospital Management"});{
"acknowledged" : true,
"insertedId" : ObjectId("5e8b4cfaef4dcbee04fbbbfc")
}
> db.demo533.insertOne({"ProjectName":"Online Library Management"});{
"acknowledged" : true,
"insertedId" : ObjectId("5e8b4d02ef4dcbee04fbbbfd")
}
> db.demo533.insertOne({"ProjectName":"Online Hospital Management"});{
"acknowledged" : true,
"insertedId" : ObjectId("5e8b4d04ef4dcbee04fbbbfe")
}
> db.demo533.insertOne({"ProjectName":"Online Customer Tracker"});{
"acknowledged" : true,
"insertedId" : ObjectId("5e8b4d0def4dcbee04fbbbff")
}Display all documents from a collection with the help of find() method −
> db.demo533.find();
This will produce the following output −
{ "_id" : ObjectId("5e8b4cfaef4dcbee04fbbbfc"), "ProjectName" : "Online Hospital Management" }
{ "_id" : ObjectId("5e8b4d02ef4dcbee04fbbbfd"), "ProjectName" : "Online Library Management" }
{ "_id" : ObjectId("5e8b4d04ef4dcbee04fbbbfe"), "ProjectName" : "Online Hospital Management" }
{ "_id" : ObjectId("5e8b4d0def4dcbee04fbbbff"), "ProjectName" : "Online Customer Tracker" }Following is the query to implement $addToSet and fetch the values of field ProjectName −
> db.demo533.aggregate(
... [
... {
... $group:
... {
... _id:null,
... SetOfProject: { $addToSet: "$ProjectName" }
... }
... }
... ]
... )This will produce the following output −
{ "_id" : null, "SetOfProject" : [ "Online Customer Tracker", "Online Library Management", "Online Hospital Management" ] }
Updated on: 14-May-2020
189 Views
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