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Articles on Trending Technologies
Technical articles with clear explanations and examples
Find oldest/ youngest post in MongoDB collection?
To find oldest/youngest post in MongoDB collection, you can use sort() with limit(1). Use ascending sort (1) for oldest and descending sort (-1) for newest posts based on date fields. Syntax // For oldest post db.collection.find().sort({"dateField": 1}).limit(1); // For newest post db.collection.find().sort({"dateField": -1}).limit(1); Sample Data db.getOldestAndYoungestPostDemo.insertMany([ { "UserId": "Larry@123", "UserName": "Larry", "UserPostDate": new ISODate('2019-03-27 12:00:00') }, ...
Read MoreOnly insert if a value is unique in MongoDB else update
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 MoreHow to count the number of documents in a MongoDB collection?
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 MoreHow to return only a single property "_id" in MongoDB?
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 MoreIs it possible to rename _id field after MongoDB group aggregation?
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 MoreQuery MongoDB with length criteria?
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 MoreHow to iterate over all MongoDB databases?
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 MoreUpsert in MongoDB while using custom _id values to insert a document if it does not exist?
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 MoreHow can I to know if my database MongoDB is 64 bits?
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 MoreAccess objects from the nested objects structure in MongoDB
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": { ...
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