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 only insert if a value is unique in MongoDB (or update if it exists), use the upsert option with the update() method. When upsert: true is specified, MongoDB performs an update if the document matches the query criteria, or inserts a new document if no match is found. Syntax db.collection.update( { field: "matchValue" }, { $set: { field: "newValue" } }, { upsert: true } ); Sample Data db.onlyInsertIfValueIsUniqueDemo.insertMany([ {"StudentName": "Larry", "StudentAge": 22}, ... Read More
To count the number of documents in a MongoDB collection, use the countDocuments() method or the legacy count() method. The countDocuments() method is recommended for accurate results. Syntax db.collectionName.countDocuments(); db.collectionName.countDocuments({query}); Create Sample Data Let us first create a collection with documents ? db.countNumberOfDocumentsDemo.insertMany([ {"CustomerName": "Bob"}, {"CustomerName": "Ramit", "CustomerAge": 23}, {"CustomerName": "Adam", "CustomerAge": 27, "CustomerCountryName": "US"} ]); { "acknowledged": true, "insertedIds": [ ... Read More
To return only the _id property in MongoDB, use the projection parameter in the find() method by setting {"_id": 1}. This filters the output to show only the _id field from all matching documents. Syntax db.collectionName.find({}, {"_id": 1}); Sample Data Let us create a collection with sample documents : db.singlePropertyIdDemo.insertMany([ {"_id": 101, "UserName": "Larry", "UserAge": 21}, {"_id": 102, "UserName": "Mike", "UserAge": 26}, {"_id": 103, "UserName": "Chris", "UserAge": 24}, {"_id": 104, "UserName": "Robert", "UserAge": 23}, ... Read More
Yes, it is possible to rename the _id field after MongoDB group aggregation using the $project stage. This technique allows you to map the _id field to a new field name while excluding the original _id from the output. Syntax db.collection.aggregate([ { $project: { _id: 0, newFieldName: "$_id", otherFields: ... Read More
To query MongoDB with length criteria, you can use the $regex operator with regular expressions to match string fields based on their character length. Syntax db.collection.find({ "fieldName": { $regex: /^.{minLength, maxLength}$/ } }); Where minLength and maxLength define the character count range. Sample Data db.queryLengthDemo.insertMany([ {"StudentFullName": "John Smith"}, {"StudentFullName": "John Doe"}, {"StudentFullName": "David Miller"}, {"StudentFullName": "Robert Taylor"}, {"StudentFullName": "Chris Williams"} ]); { ... Read More
To iterate over all MongoDB databases, you need to switch to the admin database and use the listDatabases command. This returns information about all databases in the MongoDB instance. Syntax // Switch to admin database switchDatabaseAdmin = db.getSiblingDB("admin"); // Get all database information allDatabaseName = switchDatabaseAdmin.runCommand({ "listDatabases": 1 }).databases; Example Here's how to get information about all databases ? switchDatabaseAdmin = db.getSiblingDB("admin"); allDatabaseName = switchDatabaseAdmin.runCommand({ "listDatabases": 1 }).databases; This will produce the following output ? [ { ... Read More
To perform an upsert with custom _id values in MongoDB, use update() with the upsert option instead of insert(). When you use insert() with existing _id values, MongoDB throws a duplicate key error. The upsert operation inserts a document if it doesn't exist or updates it if it does. Syntax db.collection.update( { "_id": customIdValue }, { $set: { field1: "value1", field2: "value2" } }, { upsert: true } ); Sample Data First, let's create a collection and demonstrate the duplicate key error ... Read More
You can use buildInfo along with runCommand to check whether your MongoDB database is running on 32-bit or 64-bit architecture. The key field to look for in the output is "bits". Syntax use admin db.runCommand("buildInfo") Example First, switch to the admin database and then run the buildInfo command ? use admin db.runCommand("buildInfo"); switched to db admin The output will display detailed build information about your MongoDB instance ? { "version" : "4.0.5", "gitVersion" : "3739429dd92b92d1b0ab120911a23d50bf03c412", ... Read More
To access objects from nested objects structure in MongoDB, use dot notation to traverse through multiple levels of nested documents. This allows you to query and retrieve documents based on deeply nested field values. Syntax db.collection.find({ "parentObject.childObject.nestedField": "value" }); Create Sample Data Let us first create a collection with nested documents ? db.nestedObjectDemo.insertOne({ "Student": { "StudentDetails": { "StudentPersonalDetails": { ... Read More
To search multiple fields for multiple values in MongoDB, you can use the $text and $search operators. This requires creating a text index on the fields you want to search across. Syntax db.collection.createIndex({ "field1": "text", "field2": "text" }); db.collection.find({ "$text": { "$search": "value1 value2" } }); Sample Data db.searchMultipleFieldsDemo.insertMany([ {"_id": 100, "FirstSubject": "Java", "SecondSubject": "MongoDB"}, {"_id": 101, ... Read More