Article Categories
- All Categories
-
Data Structure
-
Networking
-
RDBMS
-
Operating System
-
Java
-
MS Excel
-
iOS
-
HTML
-
CSS
-
Android
-
Python
-
C Programming
-
C++
-
C#
-
MongoDB
-
MySQL
-
Javascript
-
PHP
-
Economics & Finance
Articles on Trending Technologies
Technical articles with clear explanations and examples
Updating MongoDB collection for _id?
To update a document in MongoDB using its _id field, use the $set operator within an update operation. The _id field serves as the unique identifier for each document in a collection. Syntax db.collection.update( { _id: ObjectId("document_id") }, { $set: { field: "newValue" } } ); Sample Data Let us create a collection with sample documents ‒ db.demo741.insertMany([ { SubjectName: "MySQL" }, { SubjectName: "C" }, { SubjectName: "Java" } ]); ...
Read MoreHow to display only the keys from nested MongoDB documents?
To display only the keys from nested MongoDB documents, use the aggregation pipeline with $reduce, $map, and $objectToArray operators to extract and combine all field names from nested objects or arrays. Syntax db.collection.aggregate([ { $project: { keys: { $reduce: { ...
Read MoreHow to push value with for loop in MongoDB?
To push values with a for loop in MongoDB, use the save() method inside a for loop to insert multiple documents iteratively. This approach is useful when you need to create many similar documents programmatically. Syntax for(var i = start; i < end; i++) { db.collection.save({field1: "value", field2: "value"}); } Example Create 6 documents using a for loop ? for(var v = 1; v < 7; v++) { db.demo739.save({Name: "Chris", SubjectName: "MongoDB"}); } WriteResult({ "nInserted" : 1 }) Verify ...
Read MoreHow to order by timestamp (descending order) in MongoDB
To order by timestamp in descending order in MongoDB, use the sort() method with the timestamp field set to -1. This arranges documents from newest to oldest timestamp. Syntax db.collection.find().sort({"timestamp": -1}); Create Sample Data Let us create a collection with timestamp documents ? db.demo737.insertMany([ {"timestamp": new ISODate("2020-04-01")}, {"timestamp": new ISODate("2020-10-31")}, {"timestamp": new ISODate("2020-05-02")} ]); { "acknowledged": true, "insertedIds": [ ObjectId("5ead682157bb72a10bcf065c"), ...
Read MoreDifference between "now" and a given date with MongoDB?
To calculate the difference between the current date and a given date in MongoDB, use the $subtract operator with new Date() to get the current timestamp and subtract the stored date field. Syntax db.collection.aggregate([ { $project: { "differenceInMilliseconds": { $subtract: [new Date(), "$dateField"] }, ...
Read MoreHow to move an array of embedded documents up to parent and change key/value with aggregation pipeline?
Use $replaceRoot in MongoDB aggregation to move array elements up to the parent level and transform key/value pairs. The $replaceRoot stage replaces the input document with a new document structure. Syntax db.collection.aggregate([ { $replaceRoot: { newRoot: { $mergeObjects: [ ...
Read MoreHow to add a field with specific datatype (list, object) in an existing MongoDB document?
To add fields with specific datatypes like objects and arrays to existing MongoDB documents, use the $set operator with update() or updateOne() methods. Syntax db.collection.updateOne( { filter }, { $set: { "objectField": { key: "value" }, "arrayField": [ { item1 }, { item2 } ] }} ); Sample Data db.demo732.insertMany([ { _id: 1, Language: "English" }, ...
Read MoreHow to display a specific field in array using $project in MongoDB and ignore other fields?
To display a specific field from an array in MongoDB and ignore other fields, use the $project operator with $unwind. Set unwanted fields to 0 to exclude them from the output. Syntax db.collection.aggregate([ { $unwind: "$arrayField" }, { $match: { "arrayField.field": "value" } }, { $project: { "_id": 0, "arrayField.unwantedField": 0 } } ]); Sample Data db.demo731.insertOne({ "ProductInformation": [ { "ProductId": "Product-1", "ProductPrice": 80 }, ...
Read MoreMatch MongoDB documents with field value greater than a specific number and fetch them?
To match MongoDB documents with field values greater than a specific number, use the $gt operator in your query. This operator filters documents where the specified field value exceeds the given threshold. Syntax db.collection.find({ "fieldName": { "$gt": value } }); // Using with aggregation pipeline db.collection.aggregate([ { $match: { "fieldName": { "$gt": value } } } ]); Sample Data db.demo730.insertMany([ { "Name": "Chris", "Marks": 33 }, { "Name": "David", "Marks": 89 }, { "Name": "Chris", "Marks": ...
Read MoreMass insertion in MongoDB
For mass insertion in MongoDB, use the insertMany() method to insert multiple documents into a collection in a single operation. This is more efficient than inserting documents individually using multiple insert() calls. Syntax db.collection.insertMany([ { document1 }, { document2 }, { document3 } ]); Example Let us create a collection with multiple bank customer documents ? db.demo729.insertMany([ { BankName: "HDFC Bank", cardType: "Credit", "CustomerName": [{Name: "Chris", Age: 25}] }, { BankName: "ICICI ...
Read More