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MongoDB query for array concatenation?
To concatenate, use $concatArrays in MongoDB. Let us first create a collection with documents −
>db.demo14.insertOne({"ListOfStudent":["Carol","Mike","Sam"],"ListOfTeacher":["Robert","David"]});
{
"acknowledged" : true,
"insertedId" : ObjectId("5e0f754bd7df943a7cec4faa")
}Following is the query to display all documents from a collection with the help of find() method −
> db.demo14.find().pretty();
This will produce the following output −
{
"_id" : ObjectId("5e0f754bd7df943a7cec4faa"),
"ListOfStudent" : [
"Carol",
"Mike",
"Sam"
],
"ListOfTeacher" : [
"Robert",
"David"
]
}Following is the query to concatenate array −
> db.demo14.aggregate([
... { "$project": {
... "ListOfPeople": { "$concatArrays": [ "$ListOfStudent", "$ListOfTeacher" ] }
... }}
... ]);This will produce the following output −
{ "_id" : ObjectId("5e0f754bd7df943a7cec4faa"), "ListOfPeople" : [ "Carol", "Mike", "Sam", "Robert", "David" ] }
Updated on: 01-Apr-2020
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