To match documents in MongoDB, use $elemMatch. Let us first create a collection with documents −> db.demo15.insertOne({"Details":[{"Score":56}, {"Score":78}]}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e0f7806d7df943a7cec4fab") } > db.demo15.insertOne({"Details":[{"Score":86}, {"Score":86}]}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e0f7817d7df943a7cec4fac") } > db.demo15.insertOne({"Details":[{"Score":97}, {"Score":85}]}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e0f7823d7df943a7cec4fad") }Following is the query to display all documents from a collection with the help of find() method −> db.demo15.find();This will produce the following output −{ "_id" : ObjectId("5e0f7806d7df943a7cec4fab"), "Details" : [ { "Score" : 56 }, { "Score" : 78 } ] } { "_id" : ObjectId("5e0f7817d7df943a7cec4fac"), ... Read More

To concatenate, use $concatArrays in MongoDB. Let us first create a collection with documents −>db.demo14.insertOne({"ListOfStudent":["Carol", "Mike", "Sam"], "ListOfTeacher":["Robert", "David"]}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e0f754bd7df943a7cec4faa") }Following is the query to display all documents from a collection with the help of find() method −> db.demo14.find().pretty();This will produce the following output −{    "_id" : ObjectId("5e0f754bd7df943a7cec4faa"),    "ListOfStudent" : [       "Carol",       "Mike",       "Sam"    ],    "ListOfTeacher" : [       "Robert",       "David"    ] }Following is the query to concatenate array −> db.demo14.aggregate([ ... { ... Read More

The collMod makes it possible to add options to a collection or to modify view definitions. You can use runCommand() along with collMod(). Let us first create a collection with documents −> db.demo13.insertOne({"StudentFirstName":"Chris"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e0f730ad7df943a7cec4fa6") } > db.demo13.insertOne({"StudentFirstName":"David"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e0f7310d7df943a7cec4fa7") } > db.demo13.insertOne({"StudentFirstName":"Bob"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e0f7313d7df943a7cec4fa8") }Following is the query to display all documents from a collection with the help of find() method −> db.demo13.find();This will produce the following output −{ "_id" : ObjectId("5e0f730ad7df943a7cec4fa6"), "StudentFirstName" : "Chris" } { "_id" ... Read More

For nested search, use $and along with $or. Let us first create a collection with documents −> db.demo12.insertOne({"Name":"Chris", "Age":23, "CountryName":"US", "Message":"Hello"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e0f70a2d7df943a7cec4fa2") } > db.demo12.insertOne({"Name":"David", "Age":21, "CountryName":"US", "Message":"Hello"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e0f70acd7df943a7cec4fa3") } > db.demo12.insertOne({"Name":"Bob", "Age":23, "CountryName":"AUS", "Message":"Hi"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e0f70bad7df943a7cec4fa4") } > db.demo12.insertOne({"Name":"Carol", "Age":24, "CountryName":"US", "Message":"Hi"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e0f70c7d7df943a7cec4fa5") }Following is the query to display all documents from a collection with the help of find() method −> db.demo12.find();This will produce the following output −{ ... Read More

Let us first create a collection with documents −>db.demo11.insertOne({"ListOfStudent":[{"StudentName":"Chris", "ListOfScore":[76, 67, 54, 89]}]}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e0f6e34d7df943a7cec4fa1") }Following is the query to display all documents from a collection with the help of find() method −> db.demo11.find().pretty();This will produce the following output −{    "_id" : ObjectId("5e0f6e34d7df943a7cec4fa1"),    "ListOfStudent" : [       {          "StudentName" : "Chris",          "ListOfScore" : [             76,             67,             54,             ... Read More

For a single field, use find(). Let us first create a collection with documents −> db.demo10.insertOne({"StudentId":101, "StudentName":"Chris"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e0f68a7d7df943a7cec4f9b") } > db.demo10.insertOne({"StudentId":102, "StudentName":"David"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e0f68afd7df943a7cec4f9c") } > db.demo10.insertOne({"StudentId":103, "StudentName":"Bob"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e0f68b5d7df943a7cec4f9d") }Following is the query to display all documents from a collection with the help of find() method −> db.demo10.find();This will produce the following output −{ "_id" : ObjectId("5e0f68a7d7df943a7cec4f9b"), "StudentId" : 101, "StudentName" : "Chris" } { "_id" : ObjectId("5e0f68afd7df943a7cec4f9c"), "StudentId" : 102, "StudentName" : "David" } { "_id" ... Read More

For this, use update command and $push. Let us first create a collection with documents −>db.demo9.insertOne({"StudentDetails":[{"StudentName":"Chris", "ListOfSubject":["MySQL", "Java"]}]}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e0f6438d7df943a7cec4f94") }Following is the query to display all documents from a collection with the help of find() method −> db.demo9.find().pretty();This will produce the following output −{    "_id" : ObjectId("5e0f6438d7df943a7cec4f94"),    "StudentDetails" : [       {          "StudentName" : "Chris",          "ListOfSubject" : [             "MySQL",             "Java"          ]       ... Read More

To compare two fields, use $where in MongoDB. Let us first create a collection with documents −> db.demo7.insertOne({"FirstName1":"JOHN", "FirstName2":"John"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e0ccd1a25ddae1f53b6222f") } > db.demo7.insertOne({"FirstName1":"Carol", "FirstName2":"Mike"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e0ccd2725ddae1f53b62230") } > db.demo7.insertOne({"FirstName1":"bob", "FirstName2":"BOB"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e0ccd3225ddae1f53b62231") }Following is the query to display all documents from a collection with the help of find() method −> db.demo7.find();This will produce the following output −{ "_id" : ObjectId("5e0ccd1a25ddae1f53b6222f"), "FirstName1" : "JOHN", "FirstName2" : "John" } { "_id" : ObjectId("5e0ccd2725ddae1f53b62230"), "FirstName1" : "Carol", "FirstName2" : "Mike" } ... Read More

For this, you can use aggregate(). Let us first create a collection with documents with a vlaue as -infinity −> db.demo5.insertOne({ "_id" : 100, "seq" : 10, "Value" : -Infinity }); { "acknowledged" : true, "insertedId" : 100 } > db.demo5.insertOne({ "_id" : 101, "seq" : 10, "Value" : 50 }); { "acknowledged" : true, "insertedId" : 101 } > db.demo5.insertOne({ "_id" : 102, "seq" : 20, "Value" : 60 }); { "acknowledged" : true, "insertedId" : 102 } > db.demo5.insertOne({ "_id" : 103, "seq" : 20, "Value" : 50 }); { "acknowledged" : true, "insertedId" : 103 }Following is ... Read More

Yes, MongoDB can easily index a null value. Let us first create a collection with documents −> db.demo170.createIndex({"Value":1}, {unique:true}); {    "createdCollectionAutomatically" : true,    "numIndexesBefore" : 1,    "numIndexesAfter" : 2,    "ok" : 1 } > db.demo170.insert({"Value":100}); WriteResult({ "nInserted" : 1 }) > db.demo170.insert({"Value":null}); WriteResult({ "nInserted" : 1 }) > db.demo170.insert({"Value":90}); WriteResult({ "nInserted" : 1 }) > db.demo170.insert({"Value":78}); WriteResult({ "nInserted" : 1 })Display all documents from a collection with the help of find() method −> db.demo170.find();This will produce the following output −{ "_id" : ObjectId("5e369b789e4f06af551997da"), "Value" : 100 } { "_id" : ObjectId("5e369b7c9e4f06af551997db"), "Value" : null } { ... Read More