To update only one property, use $addToSet in MongoDB. Let us create a collection with documents −> db.demo336.insertOne({"Name":"Chris", "Score":[45, 67, 78]}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e522cb1f8647eb59e562097") } > db.demo336.insertOne({"Name":"David", "Score":[89, 93, 47]}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e522cb2f8647eb59e562098") }Display all documents from a ... Read More

For such conversion, use aggregate(). Let us create a collection with documents −> db.demo335.insertOne({"Value":"45, 67, 78.0"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e522a1cf8647eb59e562091") } > db.demo335.insertOne({"Value":"17664, 76, 534.0"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e522a26f8647eb59e562092") } > db.demo335.insertOne({"Value":"8899, 322, 135, 875.50"}); {    "acknowledged" : true, ... Read More

For this, use aggregate() in MongoDB. Let us create a collection with documents −> db.demo334.insertOne({ ...    "Name": "Chris", ...    "Age": 21, ...    "details": [{ ...       "Subject": "MySQL", ...       "Score": 78 ...    }, { ...       "Subject": "MongoDB", ... ... Read More

To count the number of documents from the collection inside the array, use aggregate(). Let us create a collection with documents −> db.demo332.insertOne({details:[{Name:"Chris", Age:21}]}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e521f16f8647eb59e56208e") } > db.demo332.insertOne({details:[{Name:"David", Age:23}, {Name:"Bob", Age:22}]}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e521f21f8647eb59e56208f") }Display all ... Read More

Let us create a collection with documents −> db.demo331.insertOne({"Words":"This is a MySQL"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e521c35f8647eb59e562089") } > db.demo331.insertOne({"Words":"THIS is a MongoDB"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e521c36f8647eb59e56208a") }Display all documents from a collection with the help of find() method−> db.demo331.find();This will ... Read More

To restrict returned data, use find(). The values 0 and 1 for fields would decide what all field values would be visible or hidden.Let us create a collection with documents −> db.demo330.insertOne({"Id":101, "Name":"Chris", "Age":21}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e52149ff8647eb59e562081") } > db.demo330.insertOne({"Id":102, "Name":"Sam", "Age":24}); {   ... Read More

For this, use $match along with aggregate(). Let us create a collection with documents −> db.demo329.insertOne({"Name":"Chris", "Age":21, "Marks":45}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e516f28f8647eb59e56207d") } > db.demo329.insertOne({"Name":"David", "Age":21, "Marks":56}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e516f28f8647eb59e56207e") } > db.demo329.insertOne({"Name":"Mike", "Age":21, "Marks":78}); {    "acknowledged" : ... Read More

The findOneAndUpdate() is used to update a single document based on the filter and sort criteria i.e. −db.collection.findOneAndUpdate(filter, update, options)Let us create a collection with documents −> db.demo328.insertOne({Name:"Chris", Marks:67}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e516b19f8647eb59e56207a") } > db.demo328.insertOne({Name:"David", Marks:78}); {    "acknowledged" : true,    "insertedId" : ... Read More

For user-defined variables, use var keyword in MongoDB. Let us create a collection with documents −> db.demo327.insertOne({"FirstName":"Chris", "LastName":"Brown"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e516952f8647eb59e562076") } > db.demo327.insertOne({"FirstName":"David", "LastName":"Miller"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e51695af8647eb59e562077") } > db.demo327.insertOne({"FirstName":"John", "LastName":"Doe"}); {    "acknowledged" : true,   ... Read More

To access array values, use dot(.) notation. Let us create a collection with documents −> db.demo326.insertOne({id:101, "ProductDetails":[{"ProductId":"Prod-101", "ProductName":"Product-1"}, ... {"ProductId":"Prod-102", "ProductName":"Product-2"} ... ] ... } ... ); {    "acknowledged" : true,    "insertedId" : ObjectId("5e516751f8647eb59e562074") } > db.demo326.insertOne({id:103, "ProductDetails":[{"ProductId":"Prod-104", "ProductName":"Product-5"}, ... {"ProductId":"Prod-105", "ProductName":"Product-6"} ... ] ... } ... ); ... Read More