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What is the $unwind operator in MongoDB?
The $unwind operator in MongoDB is the same for each array, it returns the mapping document. Here is the demo of $unwind operator in MongoDB.
To understand the concept, let us create a collection with the document. The query to create a collection with a document is as follows −
> db.unwindOperatorDemo.insertOne({"StudentName":"Larry","StudentAge":23,"StudentSubje ct":["C","C++","Java","MongoDB"]}); { "acknowledged" : true, "insertedId" : ObjectId("5c7ef5f3559dd2396bcfbfc8") }
Display all documents from a collection with the help of find() method. The query is as follows −
> db.unwindOperatorDemo.find().pretty();
The following is the output −
{ "_id" : ObjectId("5c7ef5f3559dd2396bcfbfc8"), "StudentName" : "Larry", "StudentAge" : 23, "StudentSubject" : [ "C", "C++", "Java", "MongoDB" ] }
Here is the demo of $unwind operator. The query is as follows −
> db.unwindOperatorDemo.aggregate( ... { $project : { ... StudentName : 1 , ... StudentAge: 1 , ... StudentSubject : 1 ... }}, ... { $unwind : "$StudentSubject" } ... ).pretty();
The following is the output −
{ "_id" : ObjectId("5c7ef5f3559dd2396bcfbfc8"), "StudentName" : "Larry", "StudentAge" : 23, "StudentSubject" : "C" } { "_id" : ObjectId("5c7ef5f3559dd2396bcfbfc8"), "StudentName" : "Larry", "StudentAge" : 23, "StudentSubject" : "C++" } { "_id" : ObjectId("5c7ef5f3559dd2396bcfbfc8"), "StudentName" : "Larry", "StudentAge" : 23, "StudentSubject" : "Java" } { "_id" : ObjectId("5c7ef5f3559dd2396bcfbfc8"), "StudentName" : "Larry", "StudentAge" : 23, "StudentSubject" : "MongoDB" }
Look at the sample output, the fields “StudentName” and “StudentAge” are mapping to each “StudentSubject” array field.
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