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Coalesce values from different properties into a single array with MongoDB aggregation
To coalesce values means to merge them. To merge them into a single array, use $project in MongoDB.
Let us create a collection with documents −
> db.demo244.insertOne({"Value1":10,"Value2":20});
{
"acknowledged" : true,
"insertedId" : ObjectId("5e4582e31627c0c63e7dba63")
}
> db.demo244.insertOne({"Value1":20,"Value2":30});
{
"acknowledged" : true,
"insertedId" : ObjectId("5e4582f11627c0c63e7dba64")
}Display all documents from a collection with the help of find() method −
> db.demo244.find();
This will produce the following output −
{ "_id" : ObjectId("5e4582e31627c0c63e7dba63"), "Value1" : 10, "Value2" : 20 }
{ "_id" : ObjectId("5e4582f11627c0c63e7dba64"), "Value1" : 20, "Value2" : 30 }Following is the query to coalesce values from different properties into a single array with MongoDB aggregation −
> db.demo244.aggregate([
...
... { "$group": {
... "_id": null,
... "v1": { "$addToSet": "$Value1" },
... "v2": { "$addToSet": "$Value2" }
... }},
...
... { "$project": {
... "AllValues": { "$setUnion": [ "$v1", "$v2" ] }
... }}
...]);This will produce the following output −
{ "_id" : null, "AllValues" : [ 10, 20, 30 ] }
Updated on: 30-Mar-2020
333 Views
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