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Find in MongoDB documents with filled nested array and reshape the documents result
Let us first create a collection with documents −
> db.demo187.insertOne( ... { ... "_id" : "101", ... "Details" : [ ... { "Subject" : "MongoDB" }, ... { "Subject" : "MySQL" } ... ] ... } ...); { "acknowledged" : true, "insertedId" : "101" } > db.demo187.insertOne( ... { ... "_id" : "102", ... "Details" : [ ... { } ... ] ... } ...); { "acknowledged" : true, "insertedId" : "102" } > db.demo187.insertOne( ... { ... "_id" : "103", ... "Details" : [ ... { "Subject" : "MongoDB" }, ... { "Subject" : "MySQL" } ... ] ... } ...); { "acknowledged" : true, "insertedId" : "103" }
Display all documents from a collection with the help of find() method −
> db.demo187.find();
This will produce the following output −
{ "_id" : "101", "Details" : [ { "Subject" : "MongoDB" }, { "Subject" : "MySQL" } ] } { "_id" : "102", "Details" : [ { } ] } { "_id" : "103", "Details" : [ { "Subject" : "MongoDB" }, { "Subject" : "MySQL" } ] }
Following is the query to find in MongoDB documents with filled nested array −
> db.demo187.aggregate([ ... ... {$unwind: '$Details'}, ... ... {$project: {Subject: '$Details.Subject'}}, ... ... {$match: {Subject: {$exists: true}}} ... ])
This will produce the following output −
{ "_id" : "101", "Subject" : "MongoDB" } { "_id" : "101", "Subject" : "MySQL" } { "_id" : "103", "Subject" : "MongoDB" } { "_id" : "103", "Subject" : "MySQL" }
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