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To invert the result of a MongoDB query (opposite of $and operation), use $or combined with $ne operators. This applies De Morgan's Law: NOT (A AND B) = (NOT A) OR (NOT B). Syntax db.collection.find({ $or: [ { "field1": { $ne: "value1" } }, { "field2": { $ne: "value2" } } ] }); Sample Data db.demo4.insertMany([ { uid: 1, "Name": "Chris", "Age": 22 }, ... Read More
To modify a sequence in MongoDB, use findAndModify() method to atomically increment a counter value. This approach creates auto-incrementing sequence numbers for document IDs. Syntax db.collection.findAndModify({ query: {_id: "sequenceName"}, update: {$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 More
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 More
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 More
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 More
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 More
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 More
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 More
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 More
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 More