Projection means only selected field must be visible. Set the field to 1, if you want to make it visible.Let us first create a collection with documents −> db.demo384.insertOne({"StudentName":"Chris Brown", "StudentCountryName":"US"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e5b67a022064be7ab44e7f2") } > db.demo384.insertOne({"StudentName":"David Miller", "StudentCountryName":"AUS"}); {    "acknowledged" : true, ... Read More

To filter the logs containing the word “work” , use aggregate() along with $filter. Let us first create a collection with documents −> db.demo383.insertOne( ...    { ...       "ServerName":"Jboss", ...       "ServerLogs": [ ...          { ...           ... Read More

For this, use $project and in that, $size to get the length. Let us first create a collection with documents −> db.demo382.insertOne( ...    { ... ...       "Name" : "David", ...       "details" : [ ...          { ...       ... Read More

For this, use $indexOfArray. Let us first create a collection with documents −> db.demo381.insertOne({"Values":[10, 40, 60, 30, 60]}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e5b59f72ae06a1609a00b15") } > db.demo381.insertOne({"Values":[100, 500, 700, 500, 800]}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e5b59f72ae06a1609a00b16") } > db.demo381.insertOne({"Values":[20, 40, 30, 10, 60]}); ... Read More

The $addToSet operator adds a value to an array unless the value is already present, in which case $addToSet does nothing to that array.Let us first create a collection with documents −> db.demo380.insertOne({ ... ...    "details" : [ ...       { ...          "Name" ... Read More

For projection on specific nested properties, use aggregate() in MongoDB. Let us first create a collection with documents −> db.demo379.insertOne( ...    { ...       "details1" : { ...          "details2" : { ...             "details3" : { ...   ... Read More

To manipulate subdocuments, use dot(.) notation in MongoDB. Let us first create a collection with documents −> db.demo378.insertOne( ...    { ...       Name: 'Chris', ...       details:[ ...          {id:101, Score:56}, ...          {id:102, Score:78} ...       ... Read More

To concatenate, use $concat in MongoDB aggregate(). Let us first create a collection with documents −> db.demo377.insertOne({"ListOfIds":[1001, 1002, 1003, 1004, 1005, 1006, 1007]}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e5a73462ae06a1609a00b0e") }Display all documents from a collection with the help of find() method −> db.demo377.find().pretty();This will produce the following ... Read More

To update documents, you cannot use aggregation pipeline. You can use update(). Let us first create a collection with documents −> db.demo376.insertOne( ...    { ... ...       "id" :101, ... ...       "details" : [ ...          { ...       ... Read More

JavaScript function can be saved for reuse using a system collection called system.js. To store a function, use the db.collection.save(), Let us first create a function. Following is the query −> db.system.js.save({ ...    _id: "displayMessage", ...    value: function (data) { ...       return 'The Name is: ... Read More