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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 More
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 More
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 More
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 More
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 More
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 More
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 More
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", ...] } ... Read More
To sum scores of a specific student in MongoDB, use the aggregate() method with $match to filter by student name and $sum to calculate the total score. Syntax db.collection.aggregate([ { "$match": { "Name": "StudentName" } }, { "$group": { "_id": null, "TotalScore": { "$sum": "$Score" } } } ]); Sample Data db.demo434.insertMany([ {"Name": "Chris", "Score": 45}, {"Name": "David", "Score": 55}, {"Name": "Chris", "Score": 55} ]); { ... Read More
To filter a query on specific date format in MongoDB, use the $dateToString operator within an aggregation pipeline to convert dates to string format and then match against the desired date pattern. Syntax db.collection.aggregate([ { $addFields: { stringDate: { $dateToString: { format: "%Y-%m-%d", date: "$dateField" } } } }, { $match: { "stringDate": "YYYY-MM-DD" } }, { $project: { "stringDate": 0 } } ]); Sample Data db.demo433.insertMany([ { "DueDate": new Date("2019-11-23") }, { ... Read More