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
MongoDB query by sub-field?
To query by subfield in MongoDB, use dot notation to access nested document fields. This allows you to search for specific values within embedded documents using the field.subfield syntax. Syntax db.collection.find({ "parentField.childField": "value" }) Sample Data Let's create sample documents with nested fields ? db.queryBySubFieldDemo.insertMany([ { "StudentPersonalDetails": { "StudentName": "John", "StudentHobby": "Photography" ...
Read MoreHow to convert value to string using $toString in MongoDB?
The $toString operator in MongoDB converts any value to its string representation within aggregation pipelines. It's particularly useful for converting ObjectId values, numbers, or dates to strings for display, comparison, or data transformation purposes. Syntax { $project: { fieldName: { $toString: "$fieldToConvert" } } } Sample Data db.objectidToStringDemo.insertMany([ {"UserName": "John"}, {"UserName": "Chris"}, {"UserName": "Larry"}, {"UserName": "Robert"} ]); { ...
Read MoreHow to convert ObjectId to string in MongoDB
To convert ObjectId to string in MongoDB, use the $toString operator within an aggregation pipeline. This converts the ObjectId value to its string representation. Syntax db.collection.aggregate([ { $project: { _id: { $toString: "$_id" }, // other fields as needed } } ]); Sample Data db.objectidToStringDemo.insertMany([ ...
Read MoreHow to hide _id from Aggregation?
To hide the _id field from aggregation results in MongoDB, use the $project stage with _id: 0 to exclude it while specifying other fields to include. Syntax db.collectionName.aggregate([ { $project: { _id: 0, fieldName1: 1, fieldName2: 1 } ...
Read MoreIs it possible to use MongoDB to query for entries that have a particular value in a field in an object in an array?
Yes, to query for a field in an object in the array with MongoDB, use $elemMatch operator. This operator allows you to match documents where at least one array element satisfies all specified query criteria. Syntax db.collectionName.find({ "arrayFieldName": { $elemMatch: { "fieldName": "value" } } }); Sample Data Let us create a collection with ...
Read MoreHow to print to console an object in a MongoDB script?
To print an object to the console in a MongoDB script, you can use the printjson() method for formatted output or print() with JSON.stringify() for compact output. Syntax // Method 1: Formatted output printjson({field1: "value1", field2: "value2"}); // Method 2: Compact output print(JSON.stringify({field1: "value1", field2: "value2"})); Method 1: Using printjson() (Formatted Output) The printjson() method displays objects with proper indentation and formatting ? printjson({ "UserId": 101, "UserName": "John", "UserCoreSubject": ["Java", "MongoDB", "MySQL", "SQL Server"] }); ...
Read MoreHow to retrieve a value from MongoDB by its key name?
To retrieve a value from MongoDB by its key name, use projection in the find() method to specify which fields to return while excluding others. Syntax db.collectionName.find({}, {"fieldName": 1}); Set the field value to 1 to include it, or 0 to exclude it from the result. Sample Data db.retrieveValueFromAKeyDemo.insertMany([ {"CustomerName": "Larry", "CustomerAge": 21, "CustomerCountryName": "US"}, {"CustomerName": "Chris", "CustomerAge": 24, "CustomerCountryName": "AUS"}, {"CustomerName": "Mike", "CustomerAge": 26, "CustomerCountryName": "UK"} ]); { "acknowledged": true, ...
Read MoreDelete a collection from MongoDB with special characters?
To delete a MongoDB collection that contains special characters in its name (like underscore _ or hyphen -), use the getCollection() method followed by drop(). Syntax db.getCollection("collectionNameWithSpecialChars").drop(); Create Sample Data Let us create a collection with special characters and add some documents ? db.createCollection("_personalInformation"); { "ok" : 1 } db.getCollection('_personalInformation').insertMany([ {"ClientName":"Chris", "ClientCountryName":"US"}, {"ClientName":"Mike", "ClientCountryName":"UK"}, {"ClientName":"David", "ClientCountryName":"AUS"} ]); { "acknowledged" : true, "insertedIds" : ...
Read MoreRemoving _id element from PyMongo results?
To remove the _id element from MongoDB query results, use projection with {'_id': false} in the find() method. This excludes the _id field from the returned documents. Syntax db.collection.find({}, {'_id': false}) Sample Data db.removingidElementDemo.insertMany([ {"UserName": "John", "UserAge": 21}, {"UserName": "Carol", "UserAge": 24}, {"UserName": "David", "UserAge": 22}, {"UserName": "Mike", "UserAge": 26}, {"UserName": "Chris", "UserAge": 20} ]); { "acknowledged": true, "insertedIds": [ ...
Read MoreHow to count number of keys in a MongoDB document?
There is no built-in function to count the number of keys in a MongoDB document. You need to write JavaScript code in the MongoDB shell to iterate through the document and count its fields. Syntax myDocument = db.collection.findOne({}); numberOfKeys = 0; for(key in myDocument) { numberOfKeys++; } print("Total keys: " + numberOfKeys); Sample Data Let us create a collection with a document ? db.numberofKeysInADocumentDemo.insertOne({ "UserName": "John", "UserAge": 21, "UserEmailId": "john12@gmail.com", "UserCountryName": "US" }); ...
Read More