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How can I count the documents in an array based on the value of a specific field?
For such match and count, use $match in MongoDB. Let us create a collection with documents −
> db.demo726.insertOne(
... {
... id:101,
... "details": [
... {
... Name:"Chris"
...
... },
... {
... Name:"Chris"
...
... },
... {
... Name:"Bob"
... }
... ]
... }
... );
{
"acknowledged" : true,
"insertedId" : ObjectId("5eab318643417811278f5894")
}Display all documents from a collection with the help of find() method −
> db.demo726.find();
This will produce the following output −
{ "_id" : ObjectId("5eab318643417811278f5894"), "id" : 101, "details" : [ { "Name" : "Chris" }, { "Name" : "Chris" }, { "Name" : "Bob" } ] }Following is the query to count the documents in an array based in the value of a specific field in MongoDB −
> db.demo726.aggregate([
...
... { $unwind: '$details' },
...
... { $match: { 'details.Name': "Chris"} },
... { $group: {
... _id: "$Name",
... Total_Value: { $sum: 1 }
... }
... }
... ]);This will produce the following output −
{ "_id" : null, "Total_Value" : 2 }
Updated on: 15-May-2020
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