To retrieve document from collection by _id, use find() with $in. Let us create a collection with documents −> db.demo281.insertOne({"Name":"Chris", "Age":21}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e4aac28dd099650a5401a66") } > db.demo281.insertOne({"Name":"Bob", "Age":23}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e4aac46dd099650a5401a67") } > db.demo281.insertOne({"Name":"David", "Age":28}); {    "acknowledged" ... Read More

To delete element from an array, use $pull. Let us create a collection with documents −> db.demo279.insertOne({id:[101, 103, 105, 110]}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e490af7dd099650a5401a58") } > db.demo279.insertOne({id:[107, 111, 110]}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e490b06dd099650a5401a59") }Display all documents from a collection with ... Read More

Create an index and then use explain(). Let us create a collection with documents −> db.demo278.ensureIndex({"Subjects":1}); {    "createdCollectionAutomatically" : true,    "numIndexesBefore" : 1,    "numIndexesAfter" : 2,    "ok" : 1 } > db.demo278.insertOne({"Subjects":["MySQL", "MongoDB", "Java"]}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e49096edd099650a5401a55") } > db.demo278.insertOne({"Subjects":["C", ... Read More

Let us first create a collection with documents −> db.demo277.insertOne({"details":[{"FirstName":"John"}]}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e48fb21dd099650a5401a52") } > db.demo277.insertOne({"details":[{"FirstName":"David"}]}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e48fb27dd099650a5401a53") } > db.demo277.insertOne({"details":[{"FirstName":"Chris"}]}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e48fb2bdd099650a5401a54") }Display all documents from a collection with ... Read More

To split a document by its subdocuments, use $unwind in MongoDB. Let us create a collection with documents −> db.demo276.insertOne({"Name":"Chris", "Subjects":["MySQL", "MongoDB"]}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e48f953dd099650a5401a51") }Display all documents from a collection with the help of find() method −> db.demo276.find().pretty();This will produce the following output ... Read More

To skip records in MongoDB, use skip(). With that, to display only a specific number of records, use limit().Let us create a collection with documents −> db.demo275.insertOne({"Number":10}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e48eac4dd099650a5401a43") } > db.demo275.insertOne({"Number":12}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e48eac7dd099650a5401a44") } > ... Read More

Yes, you can achieve this by indexing like “properties.k” for key and “properties.v” for value. The same is used to be implemented in ensureIndex().Let us first see an example and create a collection with documents −> db.demo274.insertOne({"details":[{StudentFirstName:"Chris", StudentLastName:"Brown"}, ...   {StudentFirstName:"David", StudentLastName:"Miller"}, ...   {StudentFirstName:"John", StudentLastName:"Smith"}, ...   {StudentFirstName:"John", StudentLastName:"Doe"} ... Read More

To insert LONG numbers, use NumberLong(). It is used to handle 64-bit integers. Let us create a collection with documents −> db.demo273.insert({ ...   Name:"Robert", ...   id: NumberLong("100000000000001"), ...   isActive:true ...}) WriteResult({ "nInserted" : 1 }) > db.demo273.insert({ ...   Name:"David", ...   id: NumberLong("98888888888888888"), ...   isActive:false ... Read More

For this, you can use aggregate() in MongoDB. Let us create a collection with documents −> db.demo149.insertOne({"Status":40}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e350386fdf09dd6d08539c4") } > db.demo149.insertOne({"Status":40}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e350388fdf09dd6d08539c5") } > db.demo149.insertOne({"Status":50}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e35038afdf09dd6d08539c6") ... Read More

To find records that does not match a condition, use $ne. Let us create a collection with documents −> db.demo148.insertOne({"Message":"Hello"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e32fb37fdf09dd6d08539c0") } > db.demo148.insertOne({"Message":"Good"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e32fb3efdf09dd6d08539c1") } > db.demo148.insertOne({"Message":"Bye"}); {    "acknowledged" : true,   ... Read More