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Articles on Trending Technologies
Technical articles with clear explanations and examples
What is the difference between deleteOne() and findOneAndDelete() operation in MongoDB?
Both deleteOne() and findOneAndDelete() remove a single document from a MongoDB collection, but they differ in their return values. The deleteOne() method returns only the deletion status, while findOneAndDelete() returns the actual deleted document. Syntax // deleteOne() - returns deletion status db.collection.deleteOne(filter, options) // findOneAndDelete() - returns deleted document db.collection.findOneAndDelete(filter, options) Sample Data db.demo448.insertMany([ {"Name": "Chris", "Age": 21}, {"Name": "David", "Age": 23}, {"Name": "Bob", "Age": 22} ]); { "acknowledged": true, ...
Read MoreHow to aggregate two collections where a field from one collection is greater than the other in MongoDB?
To aggregate two collections where a field from one collection is greater than the other in MongoDB, use $lookup to join collections, followed by $redact and $gt to filter based on field comparison. Syntax db.collection1.aggregate([ { $lookup: { "from": "collection2", "localField": "fieldName", "foreignField": "fieldName", "as": "joinedData" }}, { $unwind: "$joinedData" }, ...
Read MoreCannot push into an array from MongoDB?
To push into an array with MongoDB, use the $push operator. This operator adds a new element to the end of an existing array field in a document. Syntax db.collection.update( { }, { $push: { : } } ); Sample Data Let us create a collection with documents ? db.demo445.insertOne({ "ListOfFriends": ["Robert", "Mike", "Sam", "Carol", "David", "Mike"] }); { "acknowledged": true, "insertedId": ObjectId("5e78f099bbc41e36cc3caec2") } Display ...
Read MoreHow to improve MongoDB queries with multikey index in array?
To improve MongoDB queries with multikey index in array fields, use $elemMatch operator combined with proper compound indexes on array elements. This ensures efficient querying of nested objects within arrays. Syntax db.collection.find({ "arrayField": { $elemMatch: { "field1": "value1", "field2": "value2" } } }); Sample Data ...
Read MoreMongoDB profiler output: What is the "command" operation?
The following operations are treated as command operations in MongoDB − 1. count 2. findAndModify 3. aggregate Command operations appear in the MongoDB profiler output with the op field set to "command" and include additional details about the specific command executed. Syntax db.collection.count(query, options); db.collection.findAndModify({query, update, options}); db.collection.aggregate(pipeline, options); Sample Data Let us create a collection with documents − db.demo443.insertMany([ {"Name": "Chris"}, {"Name": "Bob"}, {"Name": "David"} ]); { "acknowledged": true, ...
Read MoreProject field in MongoDB
To project field in MongoDB, use $project in an aggregation pipeline. The $project stage allows you to reshape documents by including, excluding, or creating new fields. Syntax db.collection.aggregate([ { $project: { "fieldName": 1, // Include field "newField": "$existingField", // Rename field ...
Read MoreHow to remove duplicate record in MongoDB 3.x?
To remove duplicate records in MongoDB, use the aggregation pipeline with $group and $addToSet operators to identify duplicates, then remove them using deleteMany(). Syntax db.collection.aggregate([ { $group: { _id: { field: "$field" }, duplicateIds: { $addToSet: "$_id" }, count: { $sum: 1 } ...
Read MorePerform simple validation in MongoDB?
For validation in MongoDB, use validator with $jsonSchema to enforce document structure and data types. Validation rules are applied when creating or updating documents. Syntax db.createCollection("collectionName", { validator: { $jsonSchema: { bsonType: "object", required: ["field1", "field2"], properties: { ...
Read MoreHow to merge multiple documents in MongoDB?
To merge multiple documents in MongoDB, use the aggregate() method with operators like $group and $push to combine data from documents that share common fields. Syntax db.collection.aggregate([ { $unwind: "$arrayField" }, { $group: { _id: "$groupingField", mergedArray: { $push: "$arrayField" }, sumField: { $sum: "$numericField" } }} ]); Sample Data db.demo436.insertMany([ { ...
Read MoreHow to append to array in MongoDB?
To append to array in MongoDB, use the $concatArrays operator in aggregation pipelines to combine multiple arrays into a single array. This operator concatenates arrays and returns the combined result. Syntax db.collection.aggregate([ { $project: { newField: { $concatArrays: ["$array1", "$array2", ...] } ...
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