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To remove elements not matching conditions in MongoDB, use the $pull operator combined with query conditions. The $pull operator removes all array elements that match the specified condition. Syntax db.collection.updateMany( { "arrayField": { "$elemMatch": { "field": { "$ne": "value" } } } }, { "$pull": { "arrayField": { "field": { "$ne": "value" } } } } ); Sample Data Let us create a collection with documents ? db.demo410.insertOne({ details: [ {isMarried: false}, ... Read More
To understand how MongoDB executes queries, use the explain() method. Query plans show the execution strategy, including which indexes are used and performance statistics for query optimization. Syntax db.collection.explain().find(query); db.collection.explain("executionStats").find(query); db.collection.explain("allPlansExecution").find(query); Sample Data Let us create a collection with documents and an index ? db.demo408.insertMany([ {"Value": 50}, {"Value": 20}, {"Value": 45}, {"Value": 35} ]); { "acknowledged": true, "insertedIds": [ ... Read More
To create a new user in MongoDB, use the createUser() method on an existing database. This allows you to assign specific roles and authentication mechanisms to control user permissions. Syntax db.createUser({ user: "username", pwd: "password", roles: [ { role: "roleName", db: "databaseName" } ], mechanisms: ["SCRAM-SHA-256"] }); Example: Create User with readWrite Role Create a user named "John" with readWrite permissions on the test database ? ... Read More
To use arrays as filters when querying subdocuments in MongoDB, use the $setIsSubset operator within an aggregation pipeline. This operator checks if one array is a subset of another, making it useful for filtering array elements based on specific values. Syntax db.collection.aggregate([ { $project: { "arrayField": { $filter: { input: "$arrayField", ... Read More
The find() method in MongoDB selects documents in a collection or view and returns a cursor to the selected documents. It is the primary method for querying data from MongoDB collections. Syntax db.collection.find(query, projection) Parameters: query (optional): Specifies selection criteria using query operators projection (optional): Specifies which fields to return Sample Data Let us create a collection with sample documents ? db.demo405.insertMany([ {"StudentInfo": {"Name": "Chris"}}, {"StudentInfo": {"Name": "David"}}, {"StudentInfo": {"Name": "Bob"}}, {"StudentInfo": {"Name": ... Read More
In MongoDB versions prior to 4.0, native transactions weren't available. To implement transaction-like locking behavior, you can use findOneAndUpdate() with a lock field to ensure atomic operations on documents. Syntax db.collection.findOneAndUpdate( { "lock_field": { "$exists": false } }, { "$set": { "lock_field": true } } ) Sample Data db.demo404.insertMany([ { "FirstName": "John" }, { "FirstName": "Robert" }, { "FirstName": "Mike" } ]); { "acknowledged": true, ... Read More
To perform sort on ObjectId column in MongoDB, use the sort() method with the _id field. ObjectIds are sorted by their creation timestamp, making them useful for chronological ordering. Syntax db.collection.find().sort({_id: 1}); // Ascending (oldest first) db.collection.find().sort({_id: -1}); // Descending (newest first) Sample Data db.demo403.insertMany([ {"Name": "Chris"}, {"Name": "David"}, {"Name": "Bob"}, {"Name": "Adam"} ]); { "acknowledged": true, "insertedIds": [ ... Read More
To get intersection of two arrays in MongoDB, use $setIntersection along with aggregate(). This operator returns an array containing elements that appear in both input arrays. Syntax db.collection.aggregate([ { $project: { fieldName: { $setIntersection: ["$array1", "$array2"] } } } ]); Sample Data Let us create a collection with documents ? db.demo61.insertOne({ "Values1": ... Read More
To get date records in a range, use the $gt (greater than) and $lt (less than) operators together to define the date boundaries for your query. Syntax db.collection.find({ "dateField": { "$gt": ISODate("start-date"), "$lt": ISODate("end-date") } }); Sample Data db.demo60.insertMany([ {"ArrivalDate": new ISODate("2019-01-11 12:30:10")}, {"ArrivalDate": new ISODate("2019-10-12 03:10:00")}, {"ArrivalDate": new ISODate("2019-01-14 05:11:20")} ]); { ... Read More