Data Structure
Networking
RDBMS
Operating System
Java
MS Excel
iOS
HTML
CSS
Android
Python
C Programming
C++
C#
MongoDB
MySQL
Javascript
PHP
Economics & Finance
To select a database inside JavaScript in MongoDB, use the getSiblingDB() method with the var keyword to create a reference to another database from the current connection. Syntax var variableName = db.getSiblingDB('databaseName'); Example Let's select a database named 'sample' using getSiblingDB() ? selectedDatabase = db.getSiblingDB('sample'); sample Working with the Selected Database Now insert some documents into the selected database. Let's use a collection named 'selectDatabaseDemo' ? selectedDatabase.selectDatabaseDemo.insertMany([ {"ClientName": "John Smith", "ClientAge": 23}, {"ClientName": "Carol Taylor", "ClientAge": ... Read More
To combine update and query parts to form an upserted document in MongoDB, use the $set operator with upsert: true. This creates a new document if no match is found, or updates an existing one. Syntax db.collection.update( { queryCondition }, { $set: { field: "newValue" } }, { upsert: true } ); Sample Data db.updateWithUpsertDemo.insertMany([ { "StudentFirstName": "John", "StudentAge": 21 }, { "StudentFirstName": "Larry", "StudentAge": 23 }, { "StudentFirstName": ... Read More
To query records beginning with specific elements from an array in MongoDB, use dot notation with array index positions to match exact values at specific positions within the array. Syntax db.collection.find({ "arrayField.0": value1, "arrayField.1": value2, "arrayField.n": valueN }); Sample Data db.arrayStartsWithElementDemo.insertMany([ { "PlayerName": "Chris", "PlayerScore": [780, 9000, 456, 789, 987] }, { ... Read More
To get an element from an exact position in a nested array using MongoDB's aggregation framework, use the $slice operator within a $project stage to extract specific elements by their index position. Syntax db.collection.aggregate([ { $project: { "arrayField": { $slice: ["$arrayField", startIndex, numberOfElements] } } } ]); Sample Data db.exactPositionDemo.insertOne({ "StudentName": "John", ... Read More
The createdCollectionAutomatically field in MongoDB indicates whether an operation automatically created a collection that didn't exist. When you perform operations like createIndex() or insert() on a non-existing collection, MongoDB creates the collection automatically and returns this boolean flag as true. Syntax db.nonExistingCollection.createIndex({fieldName: 1}); // Returns: { "createdCollectionAutomatically": true, "numIndexesBefore": 1, "numIndexesAfter": 2, "ok": 1 } Example 1: Creating Index on Non-Existing Collection Let us create an index on a collection that doesn't exist ? db.createCollectionDemo.createIndex({"ClientCountryName": ... Read More
To get the MongoDB equivalent of select distinct(name) from collectionName where age = "25", use the distinct() method with a field name and query condition. This returns unique values from the specified field that match the given criteria. Syntax db.collection.distinct("fieldName", { "conditionField": value }) Sample Data db.distinctNameAndAgeDemo.insertMany([ { "ClientFirstName": "John", "Age": 23 }, { "ClientFirstName": "Larry", "Age": 25 }, { "ClientFirstName": "David", "Age": 25 }, { "ClientFirstName": "Carol", "Age": 26 }, { "ClientFirstName": ... Read More
To delete data from a MongoDB collection using multiple conditions, use deleteOne() or deleteMany() with a query document containing multiple field-value pairs. All conditions must match for the document to be deleted. Syntax db.collection.deleteOne({ "field1": "value1", "field2": "value2" }); Sample Data db.deleteDataDemo.insertMany([ {_id: 1, "Name": "Larry"}, {_id: 2, "Name": "Chris"}, {_id: 3, "Name": "Robert"}, {_id: 4, "Name": "David"}, {_id: 5, "Name": "Carol"}, ... Read More
To query for multiple parameters in MongoDB, use multiple field-value pairs in the query document separated by commas. For nested fields, use dot notation to access specific properties within embedded documents or arrays. Syntax db.collection.find({ "field1": "value1", "field2": "value2", "nestedField.subField": "value3" }); Sample Data db.multipleParametersDemo.insertMany([ { "CustomerName": "Larry", "CustomerDetails": [ ... Read More
Use the $pull operator to remove specific values from an array field in MongoDB. The $pull operator removes all instances of a value from an existing array that match a specified condition. Syntax db.collection.update( { query }, { $pull: { arrayField: value } } ); Sample Data Let us first create a collection with a document containing an array ? db.pullElementFromAnArrayDemo.insertOne({ "StudentScores": [89, 56, 78, 90] }); { "acknowledged": true, ... Read More
You can use the update command with the $set operator to add a field to existing records in MongoDB. This operation can add fields to specific documents or to all documents in a collection. Syntax db.collection.update( { query }, { $set: { "newFieldName": value } }, { multi: true } ); Sample Data db.addAFieldToEveryRecordDemo.insertMany([ { "ClientName": "Chris", "ClientAge": 34 }, { "ClientName": "Robert", "ClientAge": 36 } ]); { ... Read More