Let us create a collection with documents −> db.demo601.insertOne( ...    { ...       id:1, ...       userDetails: ...          { ...             userName:"John", ...             userMailId:"John@gmail.com" ...          } ... Read More

For this, use userAdminAnyDatabase since it gives all permission like admin. Following is the syntax −use admin db.createUser(    {       user: "yourUserName",       pwd: "yourPassword",       roles: [ { role: "yourRoleName", db: "yourDatabaseName" } ]    } )Let us implement the above syntax ... Read More

To update, use update() and following is the syntax to create and use a sample custom variable −var anyVariableName=yourValue; db.yourCollectionName.update({filter}, {$set:{yourFieldName:yourVariableName}});Let us create a collection with documents −> db.demo600.insertOne({id:1, Name:"Robert"});{    "acknowledged" : true, "insertedId" : ObjectId("5e94a063f5f1e70e134e2699") } > db.demo600.insertOne({id:2, Name:"Mike"});{    "acknowledged" : true, "insertedId" : ObjectId("5e94a06bf5f1e70e134e269a") } > ... Read More

To subtract values from document field values, use $subtract in MongoDB aggregate(). Let us create a collection with documents −> db.demo599.insertOne({"TotalPrice":250, "DiscountPrice":35});{    "acknowledged" : true, "insertedId" : ObjectId("5e948192f5f1e70e134e2696") } > db.demo599.insertOne({"TotalPrice":400, "DiscountPrice":10});{    "acknowledged" : true, "insertedId" : ObjectId("5e948199f5f1e70e134e2697") } > db.demo599.insertOne({"TotalPrice":1550, "DiscountPrice":50});{    "acknowledged" : true, "insertedId" : ... Read More

For this, use $avg along with $group and aggregate(). Let us create a collection with documents −> db.demo598.insertOne( ...    { ...       Information:'Student', ...       id:100, ...       details:[ ...          {Name:'Chris', Marks:75}, ...          {Name:'Bob', Marks:55} ... Read More

To find which document contains a specific string, use $regex along with find(). Let us create a collection with documents −> db.demo597.insertOne({"Name":"John Doe"});{    "acknowledged" : true, "insertedId" : ObjectId("5e947ae3f5f1e70e134e2690") } > db.demo597.insertOne({"Name":"John Smith"});{    "acknowledged" : true, "insertedId" : ObjectId("5e947ae8f5f1e70e134e2691") } > db.demo597.insertOne({"Name":"Chris Brown"});{    "acknowledged" : true, "insertedId" ... Read More

Use findOne() in MongoDB for this. The findOne() returns one document that satisfies the specified query criteria on the collection.Let us create a collection with documents −> db.demo596.insertOne({_id:1, "FirstName":"John", "LastName":"Smith"}); { "acknowledged" : true, "insertedId" : 1 } > db.demo596.insertOne({_id:2, "FirstName":"John", "LastName":"Doe"}); { "acknowledged" : true, "insertedId" : 2 } ... Read More

Let us create a collection with documents −> db.demo595.insertOne( { "Information": [    { "_id": new ObjectId(), Name:"Chris" },    { _id:new ObjectId(), Name:"Robert" } ] } ); {    "acknowledged" : true,    "insertedId" : ObjectId("5e93369cfd2d90c177b5bce4") }Display all documents from a collection with the help of find() method −> ... Read More

For this, use $slice. Let us create a collection with documents −> db.demo594.insertOne( ...    { ...       id:1, ...       details:[ ...          {Name:"Chris", Age:21}, ...          {Name:"Bob", Age:20}, ...          {Name:"David", Age:23}, ...     ... Read More

To fetch specific multiple documents in MongoDB, use $in. Let us create a collection with documents −> db.demo593.insertOne({id:1, "Name":"Chris"});{    "acknowledged" : true, "insertedId" : ObjectId("5e93177dfd2d90c177b5bcd9") } > db.demo593.insertOne({id:2, "Name":"John"});{    "acknowledged" : true, "insertedId" : ObjectId("5e931785fd2d90c177b5bcda") } > db.demo593.insertOne({id:3, "Name":"Bob"});{    "acknowledged" : true, "insertedId" : ObjectId("5e93178cfd2d90c177b5bcdb") } > ... Read More