To check empty field in a MongoDB collection, use $exists along with $eq operator. Let us create a collection with documents −> db.demo485.insertOne({"FirstName":"Chris", "LastName":""});{    "acknowledged" : true,    "insertedId" : ObjectId("5e82e9f6b0f3fa88e22790a8") } > db.demo485.insertOne({"FirstName":"David", "LastName":"Miller"});{    "acknowledged" : true,    "insertedId" : ObjectId("5e82e9fdb0f3fa88e22790a9") } > db.demo485.insertOne({"FirstName":"Chris", "LastName":"Brown"});{    "acknowledged" ... Read More

To search array of objects, use MongoDB find().The find() method selects documents in a collection or view and returns a cursor to the selected documents..Let us create a collection with documents −> db.demo484.insertOne( ... { 'id' : 1, 'details' : [ { 'Name1' : 'Chris' }, { 'Name2' : 'David' ... Read More

Use db.yourCollectionName.save(yourVariableName) to set variable value, wherein “yourVariableName” is your variable.Let us see an example and create a variable −> var Info={"Name":"David", ... "CountryName":"US", ... "ProjectDetails":[{"ClientName":"David", "ProjectName":"Online Banking System"}]}Following is the query to set the variable value in the save() to save the value in the collection −> db.demo483.save(Info); WriteResult({ ... Read More

To fetch specific documents, use limit() along with toArray(). The toArray() method returns an array that contains all the documents from a cursor. Let us create a collection with documents −> db.demo482.insertOne({_id:1, "StudentInformation":[{"Name":"Chris", "Age":21}]}); { "acknowledged" : true, "insertedId" : 1 } > db.demo482.insertOne({_id:2, "StudentInformation":[{"Name":"Bob", "Age":23}]}); { "acknowledged" : true, ... Read More

Use the db.collection.save() to update an existing document or inserts a new document, depending on its document parameter. Let us create a collection with documents −> db.demo481.save({"FirstName":"Chris", "LastName":"Brown"}); WriteResult({ "nInserted" : 1 }) > db.demo481.save({"FirstName":"David", "LastName":"Miller"}); WriteResult({ "nInserted" : 1 }) > db.demo481.save({"FirstName":"John", "LastName":"Doe"}); WriteResult({ "nInserted" : 1 }) > ... Read More

To format date value, use $dateToString in MongoDB. Let us create a collection with documents −> db.demo480.insertOne({id:1, "DueDate":new ISODate("2020-01-10")});{    "acknowledged" : true,    "insertedId" : ObjectId("5e821056b0f3fa88e2279098") } > db.demo480.insertOne({id:1, "DueDate":new ISODate("2017-12-21")});{    "acknowledged" : true,    "insertedId" : ObjectId("5e821062b0f3fa88e2279099") } > db.demo480.insertOne({id:1, "DueDate":new ISODate("2019-10-12")});{    "acknowledged" : true,   ... Read More

For this, use upsert and multi in MongoDB −Upsert − If set to true, creates a new document when no document matches the query criteria. The default value is false, which does not insert a new document when no match is found.Multi − f set to true, updates multiple documents ... Read More

The $unwind in MongoDB deconstructs an array field from the input documents to output a document for each element. Use $unwind along with aggregate() to get the count. Let us create a collection with documents −> db.demo478.insertOne( ... { ... ...    "Details" : { ...       _id:1, ... Read More

You can use Object.bsonsize() to get real document size. It prints the BSON size of a document in bytes. Let us create a collection with documents −> db.demo477.insertOne({"ClientId":1, "ClientName":"Chris"});{    "acknowledged" : true,    "insertedId" : ObjectId("5e82015fb0f3fa88e227908f") } > db.demo477.insertOne({"ClientId":2, "ClientName":"David"});{    "acknowledged" : true,    "insertedId" : ObjectId("5e820167b0f3fa88e2279090") } ... Read More

Use the updateMany() function to update all documents that match the filter criteria. Let us create a collection with documents −> db.demo476.insertOne({_id:1, "Name":"Chris"}); { "acknowledged" : true, "insertedId" : 1 } > db.demo476.insertOne({_id:2, "Name":"David"}); { "acknowledged" : true, "insertedId" : 2 } > db.demo476.insertOne({_id:3, "Name":"Bob"}); { "acknowledged" : true, "insertedId" ... Read More