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Concatenate with condition in MongoDB?
To concatenate with condition in MongoDB, use $cond and in that, work with $concat. Let us create a collection with documents −
> db.demo745.insertOne({Value1:"100",Value2:"100"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5eae6419a930c785c834e554")
}
> db.demo745.insertOne({Value1:"40",Value2:"50"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5eae6421a930c785c834e555")
}
> db.demo745.insertOne({Value1:"13",Value2:"45"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5eae6429a930c785c834e556")
}Display all documents from a collection with the help of find() method −
> db.demo745.find();
This will produce the following output −
{ "_id" : ObjectId("5eae6419a930c785c834e554"), "Value1" : "100", "Value2" : "100" }
{ "_id" : ObjectId("5eae6421a930c785c834e555"), "Value1" : "40", "Value2" : "50" }
{ "_id" : ObjectId("5eae6429a930c785c834e556"), "Value1" : "13", "Value2" : "45" }Followings is the query to concatenate with condition −
> db.demo745.aggregate(
... [
... { "$redact": {
... "$cond": [
... { "$eq": [
... { "$concat": [ "$Value1","$Value2" ] },
... "1345"
... ]},
... "$$KEEP",
... "$$PRUNE"
... ]
... }}
... ]
... )This will produce the following output −
{ "_id" : ObjectId("5eae6429a930c785c834e556"), "Value1" : "13", "Value2" : "45" }
Updated on: 30-Jun-2020
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