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Projection result as an array of selected items in MongoDB?
Use the distinct() for this, since it finds the distinct values for a specified field across a single collection or view and returns the results in an array.
Let us first create a collection with documents −
> db.projectionListDemo.insertOne({"_id":"1","Subject":["MongoDB","MySQL","Java"]});
{ "acknowledged" : true, "insertedId" : "1" }
> db.projectionListDemo.insertOne({"_id":"2","Subject":["MongoDB","C","C++"]});
{ "acknowledged" : true, "insertedId" : "2" }
> db.projectionListDemo.insertOne({"_id":"3","Subject":["Java","Python"]});
{ "acknowledged" : true, "insertedId" : "3" }Display all documents from a collection with the help of find() method −
> db.projectionListDemo.find().pretty();
Output
{ "_id" : "1", "Subject" : [ "MongoDB", "MySQL", "Java" ] }
{ "_id" : "2", "Subject" : [ "MongoDB", "C", "C++" ] }
{ "_id" : "3", "Subject" : [ "Java", "Python" ] }Now, let us get result as an array of selected items −
> db.projectionListDemo.distinct('_id', {'Subject' : 'MongoDB'});Output
[ "1", "2" ]
Updated on: 30-Jul-2019
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