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How to use $ifNull with MongoDB aggregation?
The $ifNull evaluates an expression and returns the value of the expression if the expression evaluates to a non-null value.
Let us first create a collection with documents −
> db.demo372.insertOne({"FirstName":"Chris"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5e591aea2ae06a1609a00af6")
}
> db.demo372.insertOne({"FirstName":null});
{
"acknowledged" : true,
"insertedId" : ObjectId("5e591aef2ae06a1609a00af7")
}
> db.demo372.insertOne({"FirstName":"David"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5e591af42ae06a1609a00af8")
}
> db.demo372.insertOne({"FirstName":null});
{
"acknowledged" : true,
"insertedId" : ObjectId("5e591afb2ae06a1609a00af9")
}Display all documents from a collection with the help of find() method −
> db.demo372.find();
This will produce the following output −
{ "_id" : ObjectId("5e591aea2ae06a1609a00af6"), "FirstName" : "Chris" }
{ "_id" : ObjectId("5e591aef2ae06a1609a00af7"), "FirstName" : null }
{ "_id" : ObjectId("5e591af42ae06a1609a00af8"), "FirstName" : "David" }
{ "_id" : ObjectId("5e591afb2ae06a1609a00af9"), "FirstName" : null }Following is the query to use $ifNull with aggregation−
> db.demo372.aggregate(
... [
... {
... $project: {
...
... FirstName: { $ifNull: [ "$FirstName", "NOT PROVIDED" ] }
... }
... }
... ]
... )This will produce the following output −
{ "_id" : ObjectId("5e591aea2ae06a1609a00af6"), "FirstName" : "Chris" }
{ "_id" : ObjectId("5e591aef2ae06a1609a00af7"), "FirstName" : "NOT PROVIDED" }
{ "_id" : ObjectId("5e591af42ae06a1609a00af8"), "FirstName" : "David" }
{ "_id" : ObjectId("5e591afb2ae06a1609a00af9"), "FirstName" : "NOT PROVIDED" }
Updated on: 02-Apr-2020
1K+ Views
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