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Articles on Trending Technologies
Technical articles with clear explanations and examples
Modify sequence in MongoDB
To modify a sequence in MongoDB, use findAndModify() method to atomically increment a counter value. This approach creates auto-incrementing sequence numbers for document IDs. Syntax db.collection.findAndModify({ query: {_id: "sequenceName"}, update: {$inc: {sequence_value: 1}}, new: true }); Create Sample Data First, create a collection with an initial document ? db.demo261.insertOne({_id:100, Name:"Chris"}); { "acknowledged" : true, "insertedId" : 100 } db.demo261.find(); { "_id" : 100, "Name" : "Chris" } Example: Create ...
Read MoreGet MongoDB documents that contains specific attributes in array
To get MongoDB documents that contain specific attributes in an array, use $and along with dot notation to match multiple field values within the same array field. Syntax db.collection.find({ $and: [ {"arrayField.attribute1": "value1"}, {"arrayField.attribute2": "value2"} ] }); Sample Data Let us first create a collection with documents − db.demo2.insertMany([ { "StudentInformation": [ ...
Read MoreHow to run MongoDB shell using mongos command?
The mongos command is used to start a MongoDB router process in sharded cluster deployments. It acts as an interface between client applications and the sharded cluster, routing queries to the appropriate shards. Syntax mongos --configdb /, Basic mongos Command To start the mongos router, specify the configuration replica set ? mongos --configdb configReplSet/config1.example.com:27019, config2.example.com:27019, config3.example.com:27019 Common mongos Options Here are the most frequently used mongos command options ? mongos --configdb configReplSet/config1:27019, config2:27019 --port 27017 mongos --configdb configReplSet/config1:27019, config2:27019 --logpath /var/log/mongodb/mongos.log mongos --configdb configReplSet/config1:27019, config2:27019 --fork --logpath ...
Read MoreHow to update % printed to Console from MongoDB?
To update and print percentage values to console from MongoDB script, create a variable with your numeric value and use the print() method with toFixed() to format decimal places. Syntax var variableName = numericValue; print(variableName.toFixed(decimalPlaces) + " %"); Example Create a variable with a percentage value and format it to 2 decimal places ? var amount = 10.58945; print(amount.toFixed(2) + " %"); The output of the above code is ? 10.59 % Key Points Use toFixed() to control the number of decimal places displayed. ...
Read MoreInvoke convertToCapped and convert an existing collection to capped in MongoDB
To convert an existing collection to capped in MongoDB, use the convertToCapped command with runCommand(). A capped collection has a fixed size and automatically removes old documents when the size limit is reached. Syntax db.runCommand({ convertToCapped: "collectionName", size: sizeInBytes }); Sample Data Let us create a regular collection with some documents ? db.demo260.insertMany([ {"Name": "Chris"}, {"Name": "Bob"}, {"Name": "David"} ]); { "acknowledged": true, ...
Read MoreMongoDB inverse of query to return all items except specific documents?
To get documents except some specific documents, use $nor along with $and. The $nor operator returns documents that do not match any of the specified conditions, making it perfect for inverse queries. Syntax db.collection.find({ $nor: [ { $and: [{ field1: value1 }, { field2: value2 }] } ] }); Sample Data Let us first create a collection with sample student documents — db.demo1.insertMany([ { "StudentName": "Chris", "StudentMarks": 38 }, ...
Read MoreHow to specify the order in which the query returns matching documents in MongoDB
To specify the order in which the query returns matching documents, use cursor.sort() in MongoDB. The cursor is obtained from db.collectionName.find(). Syntax db.collection.find().sort({ field: 1 }); // Ascending order db.collection.find().sort({ field: -1 }); // Descending order Where 1 means ascending order and -1 means descending order. Sample Data Let us create a collection with documents − db.demo259.insertMany([ { "Subject": "MySQL" }, { "Subject": "Java" }, { "Subject": "MongoDB" } ]); { ...
Read MoreHow to pull value from array of ObjectIDs in MongoDB?
To pull value from array of ObjectIDs in MongoDB, use the $pull operator with the $in operator to match and remove specific ObjectID values from the array. Syntax db.collection.update( { /* query */ }, { $pull: { arrayField: { $in: [ObjectId("id1"), ObjectId("id2")] } } } ); Sample Data Let us create a collection with documents ? db.demo258.insertOne({ "arrayOfObjectsId": [ ObjectId("5e47a5e81627c0c63e7dba92"), ObjectId("5e47a5e51627c0c63e7dba91") ...
Read MoreSet MongoDB compound index with a fixed value field
A MongoDB compound index with a fixed value field ensures uniqueness across multiple fields, including fields that may be missing (null) in some documents. When you create a unique compound index, MongoDB treats missing fields as null values. Syntax db.collection.createIndex( { "field1": 1, "field2": 1 }, { unique: true } ); Create Sample Data First, let's create a unique compound index on StudentName and StudentAge ? db.compoundIndexDemo.createIndex( {"StudentName": 1, "StudentAge": 1}, {unique: true} ); ...
Read MoreUpdate MongoDB variable value with variable itself?
To update a MongoDB field value using its current value as part of the new value, use the $set operator with string concatenation or the $concat aggregation operator within an update pipeline. Syntax // Using aggregation pipeline (recommended) db.collection.updateMany( {}, [{ $set: { fieldName: { $concat: ["$fieldName", " additional text"] } } }] ); // Using $set with literal string (replaces with literal text) db.collection.update( {}, { $set: { fieldName: "fieldName additional text" } } ); Sample Data ...
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