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Query array of subdocuments in MongoDB
To query an array of subdocuments, use $unwind in MongoDB. Let us create a collection with documents −
> db.demo499.insertOne({
... "details":
... [
... {
... Name :"MIT",
... Rank: 1,
... "CountryName":"US"
... },
...
... {
... Name :"Stanford University",
... Rank: 2
... },
...
... {
... Name :"University of California, Berkeley",
... Rank: 3
... }
... ]
... }
... );
{
"acknowledged" : true,
"insertedId" : ObjectId("5e87433d987b6e0e9d18f558")
}Display all documents from a collection with the help of find() method −
> db.demo499.find();
This will produce the following output −
{ "_id" : ObjectId("5e87433d987b6e0e9d18f558"), "details" : [ { "Name" : "MIT", "Rank" : 1,
"CountryName" : "US" }, { "Name" : "Stanford University", "Rank" : 2 }, { "Name" : "University
of California, Berkeley", "Rank" : 3 } ] }Following is how to query an array of subdocuments −
> db.demo499.aggregate({$unwind: "$details"},
... {$match: {"details.CountryName":{$exists: true}}},
... {$project: {"details.Name": 1, "details.CountryName": 1, "_id": 0}})This will produce the following output −
{ "details" : { "Name" : "MIT", "CountryName" : "US" } }
Updated on: 13-May-2020
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