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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" }
Updated on: 2020-03-27T08:13:08+05:30
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