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 find matching documents given an array with values in MongoDB, use the $in operator. This operator matches documents where the array field contains any of the specified values. Syntax db.collection.find({ "arrayField": { $in: ["value1", "value2", "value3"] } }); Create Sample Data Let us create a collection with documents containing project arrays ? db.demo511.insertMany([ { "ListOfProject": ["Library Management System", "Hospital Management System"] }, { ... Read More
To match and group array elements with the maximum value in MongoDB aggregation, use $filter with $max to find elements with the highest score, then $group to count occurrences by name. Syntax db.collection.aggregate([ { "$project": { "maxElement": { "$arrayElemAt": [ ... Read More
To implement MongoDB $addToSet for an array within an array and append a value, use the update() method with dot notation to target the specific nested array. The $addToSet operator adds a value to an array only if it doesn't already exist, preventing duplicates. Syntax db.collection.update( {query}, { $addToSet: { "parentArray.index.nestedArray": value } } ); Sample Data db.demo509.insertOne({ "value1": [ { ... Read More
Yes, MongoDB tracks index usage statistics through the $indexStats aggregation stage. This allows you to monitor how frequently each index is accessed, helping optimize database performance by identifying unused or heavily used indexes. Syntax db.collection.aggregate([ { $indexStats: {} } ]); Create Sample Data First, let's create an index on the FirstName field − db.demo508.createIndex({"FirstName": 1}); { "createdCollectionAutomatically": true, "numIndexesBefore": 1, "numIndexesAfter": 2, "ok": 1 } Now insert ... Read More
To filter and fetch specific fields from objects in MongoDB, use the aggregation pipeline combining $match, $project, and $filter operators to target specific array elements and extract only the desired fields. Syntax db.collection.aggregate([ { $match: { "arrayField.field": "value" } }, { $project: { arrayField: { $filter: { input: "$arrayField", ... Read More
To find a user by name in MongoDB, use the find() method with a query document that specifies the name field and its value. This performs an exact match search on the specified field. Syntax db.collection.find({"fieldName": "value"}); Create Sample Data Let us create a collection with user documents − db.demo504.insertMany([ {"Name": "Chris"}, {"Name": "John"}, {"Name": "David"} ]); { "acknowledged": true, "insertedIds": [ ... Read More
To slice arrays in MongoDB, use the $slice operator in the projection part of your query. This allows you to return only a portion of an array field from documents. Syntax db.collection.find( { query }, { "arrayField": { $slice: count } } ); Where count can be: Positive number: Returns first N elements Negative number: Returns last N elements [skip, limit]: Skips elements and returns limited count Sample Data db.demo503.insertMany([ {_id:1, Name:"John", Subject:["MySQL", "Java", "C"]}, ... Read More
To query MongoDB for a field combination of FirstName and LastName, use $concat to combine the fields into a single string and $eq to check equality against your target value. Syntax db.collection.aggregate([ { "$redact": { "$cond": [ { "$eq": [ ... Read More
To group duplicate documents in MongoDB, use the $group stage in the aggregation pipeline. This operation groups documents by a specified field and eliminates duplicates by creating a single document per unique value. Syntax db.collection.aggregate([ { $group: { _id: "$fieldName" } } ]); Sample Data db.demo501.insertMany([ { "Name": "Chris" }, { "Name": "Bob" }, { "Name": "Chris" }, { "Name": "John" }, { "Name": "Chris" }, ... Read More
To select the 10 most recent documents in MongoDB without changing their order, use the skip() method with count() - 10. This skips the oldest documents and returns the last 10 in their original insertion order. Syntax db.collection.find().skip(db.collection.count() - 10); Create Sample Data db.demo500.insertMany([ {value: 10}, {value: 1200}, {value: 19}, {value: 28}, {value: 50}, {value: 70}, {value: 100}, {value: 10}, ... Read More