The $unwind in MongoDB deconstructs an array field from the input documents to output a document for each element.$group is used to group input documents by the specified _id expression and for each distinct grouping, outputs a document.$project is used to pass along the documents with the requested fields to the next stage in the pipeline.Let us create a collection with documents −> db.demo238.insertOne( ...   { ... ...      "EmailId" : "John@gmail.com", ...      "details" : [ ...         { ...            "Name" : "Bob", ...         ... Read More

Set the field you don’t want to include as 0. This would display rest of the values while using find(). Let us first create a collection with documents −> db.demo237.insertOne({ ...   _id:101, ...   Product: { ...      description1: {id:1001 }, ...      description2: {Name:"Product-1" }, ...      description3: {Price:550 } ...   } ...} ...); { "acknowledged" : true, "insertedId" : 101 }Display all documents from a collection with the help of find() method −> db.demo237.find().pretty();This will produce the following output −{    "_id" : 101,    "Product" : {       "description1" : ... Read More

To sort, use $sort in MongoDB. Let us create a collection with documents −> db.demo236.insertOne({"details":{"Name":"Chris", "Age":21}}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e419015f4cebbeaebec514c") } > db.demo236.insertOne({"details":{"Name":"David", "Age":23}}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e41901cf4cebbeaebec514d") } > db.demo236.insertOne({"details":{"Name":"Bob", "Age":24}}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e419023f4cebbeaebec514e") }Display all documents from a collection with the help of find() method −> db.demo236.find();This will produce the following output −{ "_id" : ObjectId("5e419015f4cebbeaebec514c"), "details" : { "Name" : "Chris", "Age" : 21 } } { "_id" : ObjectId("5e41901cf4cebbeaebec514d"), "details" : { "Name" : "David", "Age" : 23 } } ... Read More

To get inner value of JSON data, use find() along with dot(.) notation. Let us create a collection with documents −> db.demo235.insertOne( ...   { ...      "id":101, ...      "details":[ ...         { ...            "Name":"Chris Brown", ...            "Age":21 ...         }, ...         { ...            "Name":"David Miller", ...            "Age":24 ...         } ...      ], ...      "otherdetails":[ ...         ... Read More

To check for existence, use $exists. Let us create a collection with documents − > db.demo234.insertOne({"FirstName":"Chris", "LastName":"Brown", "Age":24}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e418a50f4cebbeaebec5148") } > db.demo234.insertOne({"FirstName":"David", "LastName":"Miller"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e418a5ff4cebbeaebec5149") } > db.demo234.insertOne({"FirstName":"John", "LastName":"Smith", Age:34}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e418a70f4cebbeaebec514a") }Display all documents from a collection with the help of find() method −> db.demo234.find();This will produce the following output −{ "_id" : ObjectId("5e418a50f4cebbeaebec5148"), "FirstName" : "Chris", "LastName" : "Brown", "Age" : 24 } { "_id" : ObjectId("5e418a5ff4cebbeaebec5149"), "FirstName" : "David", "LastName" : "Miller" } { "_id" : ... Read More

To limit the amount of characters returned from a field, use $substr in MongoDB. Let us create a collection with documents −> db.demo233.insertOne({"Paragraph":"My Name is John Smith.I am learning MongoDB database"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e41877df4cebbeaebec5146") } > db.demo233.insertOne({"Paragraph":"David Miller is a good student and learning Spring and Hibernate Framework."}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e4187d7f4cebbeaebec5147") }Display all documents from a collection with the help of find() method −> db.demo233.find().pretty();This will produce the following output −{    "_id" : ObjectId("5e41877df4cebbeaebec5146"),    "Paragraph" : "My Name is John Smith.I am learning MongoDB database" } ... Read More

Let us first create a collection with documents −> db.demo232.insertOne({_id:101, Name:"Chris"}); { "acknowledged" : true, "insertedId" : 101 } > db.demo232.insertOne({_id:102, Name:"Bob"}); { "acknowledged" : true, "insertedId" : 102 } > db.demo232.insertOne({_id:103, Name:"Bob"}); { "acknowledged" : true, "insertedId" : 103 } > db.demo232.insertOne({_id:104, Name:"David"}); { "acknowledged" : true, "insertedId" : 104 } > db.demo232.insertOne({_id:105, Name:"Chris"}); { "acknowledged" : true, "insertedId" : 105 }Display all documents from a collection with the help of find() method −> db.demo232.find();This will produce the following output −{ "_id" : 101, "Name" : "Chris" } { "_id" : 102, "Name" : "Bob" } { "_id" : ... Read More

To sum the array size fields, use $sum along with $size. Let us create a collection with documents −> db.demo231.insertOne({"Subjects":["MongoDB", "MySQL", "SQL Server"]}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e3fc73ff4cebbeaebec5143") } > db.demo231.insertOne({"Subjects":["Java", "C", "C++"]}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e3fc757f4cebbeaebec5144") } > db.demo231.insertOne({"Subjects":["Python", "Spring"]}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e3fc762f4cebbeaebec5145") }Display all documents from a collection with the help of find() method −> db.demo231.find();This will produce the following output −{ "_id" : ObjectId("5e3fc73ff4cebbeaebec5143"), "Subjects" : [ "MongoDB", "MySQL", "SQL Server" ] } { "_id" : ObjectId("5e3fc757f4cebbeaebec5144"), "Subjects" : [ "Java", "C", ... Read More

The findOne() in MongoDB returns only a single document. Let us create a collection with documents −> db.demo230.insertOne({"FirstName":"Chris"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e3fc4d2f4cebbeaebec513e") } > db.demo230.insertOne({"FirstName":"Bob"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e3fc4d5f4cebbeaebec513f") } > db.demo230.insertOne({"FirstName":"Chris"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e3fc4dbf4cebbeaebec5140") } > db.demo230.insertOne({"FirstName":"David"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e3fc4dff4cebbeaebec5141") } > db.demo230.insertOne({"FirstName":"David"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e3fc4e1f4cebbeaebec5142") }Display all documents from a collection with the help of find() method −> db.demo230.find();This will produce the following output −{ "_id" : ObjectId("5e3fc4d2f4cebbeaebec513e"), "FirstName" : ... Read More

For sparse index, use sparse:true. Following is the query to create an index −> db.demo229.ensureIndex({"ClientName":1}, {unique: true}); {    "createdCollectionAutomatically" : true,    "numIndexesBefore" : 1,    "numIndexesAfter" : 2,    "ok" : 1 }Following is the query to display indexes −> db.demo229.getIndexes();This will produce the following output −[    {       "v" : 2,       "key" : {          "_id" : 1       },       "name" : "_id_",       "ns" : "test.demo229"    },    {       "v" : 2,       "unique" ... Read More