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MongoDB query to concatenate values of array with other fields
To concatenate in MongoDB, use $concat in $project. Let us create a collection with documents −
> db.demo359.insertOne( ... { ... ... Name1: "Chris", ... Name2: "David", ... Subjects: ["MySQL","MongoDB","Java"] ... } ... ); { "acknowledged" : true, "insertedId" : ObjectId("5e5694cdf8647eb59e5620d0") }
Display all documents from a collection with the help of find() method −
> db.demo359.find().pretty();
This will produce the following output −
{ "_id" : ObjectId("5e5694cdf8647eb59e5620d0"), "Name1" : "Chris", "Name2" : "David", "Subjects" : [ "MySQL", "MongoDB", "Java" ] }
Following is the query to concatenate values of the array with other fields −
> db.demo359.aggregate([ ... { ... $project: { ... values: { ... $reduce: { ... input: '$Subjects', ... initialValue: '', ... in: { ... $concat: ['$$value',' ','$$this'] ... } ... } ... }, ... Name1: 1 ... } ... }, ... { ... $project: { ... 'ConcatResult': { '$concat': [ '$Name1', '$values'] } ... } ... } ... ]) { "_id" : ObjectId("5e5694cdf8647eb59e5620d0"), "ConcatResult" : "Chris MySQL MongoDB Java" }
This will produce the following output −
{ "_id" : ObjectId("5e5694cdf8647eb59e5620d0"), "ConcatResult" : "Chris MySQL MongoDB Java" }
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