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Query on the last object of an array with MongoDB
To query on the last object of an array, use aggregate(). Let us create a collection with documents −
> db.demo103.insertOne( { "Details" : [
{ "StudentId" : 101, "Details" : "MongoDB" },
{"StudentId" : 102, "Details" : "MySQL" },
{ "StudentId" : 103, "Details" : "Java" }
], "Details1" : [ { "StudentId" : 104, "Number" : 3 } ] } );
{
"acknowledged" : true,
"insertedId" : ObjectId("5e2ed2dd9fd5fd66da21446e")
}Display all documents from a collection with the help of find() method −
> db.demo103.find();
This will produce the following output −
{ "_id" : ObjectId("5e2ed2dd9fd5fd66da21446e"), "Details" : [ { "StudentId" : 101, "Details" : "MongoDB" }, { "StudentId" : 102, "Details" : "MySQL" }, { "StudentId" : 103, "Details" : "Java" } ], "Details1" : [ { "StudentId" : 104, "Number" : 3 } ] }Here is how you can query to on the last object of an array −
> db.demo103.aggregate([ { $project: { Details1: 1, Details: {$arrayElemAt: ["$Details", -1]} } }, { $match: {"Details.StudentId": 103} } ])This will produce the following output −
{ "_id" : ObjectId("5e2ed2dd9fd5fd66da21446e"), "Details1" : [ { "StudentId" : 104, "Number" : 3 } ], "Details" : { "StudentId" : 103, "Details" : "Java" } }
Updated on: 30-Mar-2020
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