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To remove an entire array field from all documents in a MongoDB collection, use the $unset operator. This completely removes the specified field from the documents. Syntax db.collection.updateMany( {}, { $unset: { "arrayFieldName": "" } } ); Sample Data Let us create a collection with documents containing array fields ? db.demo609.insertMany([ { "ListOfSubject": ["MySQL", "MongoDB"] }, { "ListOfSubject": ["Java"] } ]); { "acknowledged": true, "insertedIds": [ ... Read More
To get unique values within two arrays in a MongoDB document, use the $setUnion operator in the aggregation pipeline. The $setUnion takes two or more arrays and returns an array containing the unique elements that appear in any input array. Syntax db.collection.aggregate([ { $project: { uniqueArray: { $setUnion: ["$array1", "$array2"] } } } ]) Sample Data Let us ... Read More
To update a nested document in MongoDB, use the update() method with dot notation to specify the path to the nested field. This allows you to modify deeply embedded values without affecting the parent document structure. Syntax db.collection.update( { "filterField": "value" }, { $set: { "parentField.nestedField.targetField": "newValue" } } ); Sample Data Let us create a collection with a nested document structure ? db.demo607.insertOne({ id: 1, "Info1": { ... Read More
To get a rating average in MongoDB based on duplicate ids, use the $avg operator with $group. The $ifNull operator handles null rating values by treating them as zero in the calculation. Syntax db.collection.aggregate([ { "$group": { "_id": "$fieldToGroupBy", "averageField": { "$avg": { "$ifNull": ["$ratingField", 0] } } } ... Read More
To update quantity in MongoDB based on two conditions, use the update() method with multiple filter criteria. Combine document-level and array element conditions to target specific nested objects. Syntax db.collection.update( { "documentField": "value", "arrayField.nestedField": "arrayValue" }, { $set: { "arrayField.$.targetField": newValue } } ); Sample Data db.demo605.insertMany([ { _id: 1, ... Read More
To remove duplicates from a MongoDB collection, create a unique index on the field that should not have duplicate values. This prevents duplicate insertion and removes existing duplicates when combined with the dropDups option. Syntax db.collectionName.createIndex( { fieldName: 1 }, { unique: true, dropDups: true } ); Example: Preventing Duplicate FirstNames Let's create a unique index on the FirstName field to prevent duplicates ? db.demo604.createIndex( { FirstName: 1 }, { unique: true, dropDups: true ... Read More
The NumberLong(x) function can lose precision with very large integers due to JavaScript's number limitations, while NumberLong("x") preserves exact precision by accepting the number as a string. Syntax NumberLong(number) // May lose precision for very large values NumberLong("string") // Preserves exact precision Example Let us create a collection with documents to demonstrate the difference ? db.demo603.insertMany([ {"longValue": NumberLong(988998985857575789)}, {"longValueInString": NumberLong("988998985857575789")} ]); { "acknowledged": true, "insertedIds": ... Read More
To aggregate elements with similar ids in different documents, use $group in MongoDB aggregation pipeline. This technique groups documents by id and collects all related data into arrays. Syntax db.collection.aggregate([ { $group: { '_id': { id: "$id", "fieldName": "$fieldName" }, "count": { "$sum": 1 } }}, { $group: { '_id': "$_id.id", "aggregatedData": { ... Read More
To update a document in MongoDB without overwriting the entire document, use the $set operator to modify specific fields while preserving existing data. This prevents accidental data loss during updates. Syntax db.collection.update( { "field": "matchValue" }, { $set: { "fieldToUpdate": "newValue" } } ); Sample Data db.demo601.insertMany([ { id: 1, userDetails: { userName: ... Read More
To create a new user and set their role in MongoDB, use the createUser() method. The userAdminAnyDatabase role provides comprehensive administrative privileges across all databases. Syntax use admin db.createUser( { user: "yourUserName", pwd: "yourPassword", roles: [ { role: "yourRoleName", db: "yourDatabaseName" } ] } ) Example Create a user with the "userAdminAnyDatabase" role ? use admin db.createUser( ... Read More