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 ... 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" }, ... ... 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" : ... 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", ...     ... 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,   ... 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 ... 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" : ... 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"]}); ... 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" : ... 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 −[   ... Read More