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Articles on Trending Technologies
Technical articles with clear explanations and examples
MongoDB query to update array object in index N?
To update an array object at a specific index in MongoDB, use the $ positional operator with dot notation. The $ operator identifies the matched array element, allowing you to update its nested fields. Syntax db.collection.update( {"arrayField.matchingField": "value"}, {$set: {"arrayField.$.nestedField": "newValue"}} ) Sample Data db.demo489.insertOne({ details: [ { id: 101, ...
Read MoreHow to delete partial data in MongoDB?
To delete partial data in MongoDB, you can combine find() with skip() and limit() methods to target specific documents, then use deleteMany() with the $in operator to remove them efficiently. Syntax var ids = db.collection.find({}, {_id: 1}).skip(N).toArray().map(function(d) { return d._id; }); db.collection.deleteMany({_id: {$in: ids}}); Sample Data db.demo488.insertMany([ {"Name": "Chris"}, {"Name": "David"}, {"Name": "Bob"}, {"Name": "Mike"}, {"Name": "Sam"}, {"Name": "John"}, ...
Read MoreImplement a query similar to MySQL Union with MongoDB?
To implement a query similar to MySQL UNION in MongoDB, use the $lookup aggregation stage to join collections, followed by $group and $project to combine and format results. This approach joins collections based on matching fields rather than simply concatenating rows. Syntax db.collection1.aggregate([ { $lookup: { from: "collection2", localField: "matchField", foreignField: "matchField", as: "joinedData" ...
Read MoreHow to check empty field in a MongoDB collection?
To check empty field in a MongoDB collection, use $exists along with $eq operator. The $exists ensures the field is present, while $eq matches the empty string value. Syntax db.collection.find({ "fieldName": { "$exists": true, "$eq": "" } }); Create Sample Data Let us create a collection with documents containing empty and non-empty fields ? db.demo485.insertMany([ {"FirstName": "Chris", "LastName": ""}, {"FirstName": ...
Read MoreSearch array of objects in a MongoDB collection?
To search array of objects in MongoDB, use the find() method with dot notation to target specific fields within array elements. The find() method selects documents in a collection and returns a cursor to the matched documents. Syntax db.collection.find({ "arrayField.objectProperty": "value" }); // Multiple conditions with $or db.collection.find({ $or: [ {"arrayField.property1": "value1", "arrayField.property2": "value2"}, {"arrayField.property1": "value3", "arrayField.property2": "value4"} ] }); Sample Data Let us create ...
Read MoreSet variable value in MongoDB save() method
To set a variable value in MongoDB's save() method, use db.collectionName.save(variableName) where variableName is your JavaScript variable containing the document data. Syntax var variableName = { field1: "value1", field2: "value2" }; db.collectionName.save(variableName); Example Let us create a variable with document data and save it to a collection ? Step 1: Create a Variable var Info = { "Name": "David", "CountryName": "US", "ProjectDetails": [ { ...
Read MoreFetch specific documents with array values in MongoD
To fetch specific documents with array values in MongoDB, use the limit() method combined with toArray(). The toArray() method returns an array containing all documents from a cursor, while limit() restricts the number of documents returned. Syntax db.collection.find().limit(numberOfDocuments).toArray() Create Sample Data Let us create a collection with documents containing array values ? db.demo482.insertMany([ {_id:1, "StudentInformation":[{"Name":"Chris", "Age":21}]}, {_id:2, "StudentInformation":[{"Name":"Bob", "Age":23}]}, {_id:3, "StudentInformation":[{"Name":"David", "Age":20}]} ]); { "acknowledged" : true, "insertedIds" : ...
Read MoreHow to use save() correctly in MongoDB?
The save() method in MongoDB is used to insert a new document or update an existing document based on whether the document contains an _id field. If no _id is provided, it inserts a new document. If an _id exists, it updates the existing document. Syntax db.collection.save(document) Create Sample Data Let us create a collection with documents using save() ? db.demo481.save({"FirstName":"Chris", "LastName":"Brown"}); db.demo481.save({"FirstName":"David", "LastName":"Miller"}); db.demo481.save({"FirstName":"John", "LastName":"Doe"}); db.demo481.save({"FirstName":"John", "LastName":"Smith"}); WriteResult({ "nInserted" : 1 }) WriteResult({ "nInserted" : 1 }) WriteResult({ "nInserted" : 1 }) WriteResult({ "nInserted" : 1 }) ...
Read MoreFormat date value in MongoDB shell?
To format date values in MongoDB shell, use the $dateToString operator within an aggregation pipeline. This operator converts ISODate values into custom formatted strings according to your specified format pattern. Syntax { "$dateToString": { "format": "formatString", "date": "$dateField" } } Sample Data db.demo480.insertMany([ { "id": 1, "DueDate": new ISODate("2020-01-10") }, { "id": 1, "DueDate": new ISODate("2017-12-21") }, ...
Read MoreMongoDB query to add timestamp only if it is not present
To add a timestamp field only if it is not already present in MongoDB documents, use the $exists operator with update() and set multi: true to update multiple documents at once. Syntax db.collection.update( { "fieldName": { $exists: false } }, { $set: { "fieldName": new Date() } }, { multi: true } ); Sample Data db.demo479.insertMany([ { "DueDate": ISODate("2020-01-10"), "Name": "Chris" }, { "Name": "David" }, { "DueDate": ISODate("2019-12-31"), ...
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