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Articles on Trending Technologies
Technical articles with clear explanations and examples
Min and max values of an array in MongoDB?
To find the minimum and maximum values from array elements in MongoDB, use the $min and $max operators within an aggregation pipeline. These operators work on array fields to extract the smallest and largest values respectively. Syntax db.collection.aggregate([ { $project: { "minField": { $min: "$arrayField.property" }, "maxField": { $max: "$arrayField.property" } } ...
Read MoreWhat is the BSON query for the command 'show dbs' (list of databases) in MongoDB?
The BSON equivalent of the show dbs command in MongoDB is the listDatabases administrative command. This command must be run against the admin database to retrieve information about all databases on the MongoDB instance. Syntax db.runCommand({ listDatabases: 1 }) Example First, switch to the admin database ? use admin switched to db admin Now, run the listDatabases command ? db.runCommand({ listDatabases: 1 }) This will produce the following output ? { "databases": [ ...
Read MoreMongoDB query to limit subdocuments having the given fields of the 'projection'
To limit subdocuments having specific fields during projection in MongoDB, use the aggregation pipeline with $match, $unwind, and $project stages to filter and reshape the data. Syntax db.collection.aggregate([ { $match: { "arrayField.targetField": { $exists: 1 } } }, { $unwind: "$arrayField" }, { $match: { "arrayField.targetField": { $exists: 1 } } }, { $project: { "newField": "$arrayField.targetField", "_id": 0 } } ]); Sample Data db.demo285.insertOne({ details: [ ...
Read MoreExport specified field of a collection in mongodb / mongodump to file?
To export specified fields from a MongoDB collection, use the mongoexport command with the -f parameter to specify which fields to export. This utility allows you to export data in various formats including CSV and JSON. Syntax mongoexport -d yourDatabaseName -c yourCollectionName -f yourFieldName --type=csv -o yourFileLocation/FileName Sample Data Let us create a collection with sample documents ? db.demo284.insertMany([ {"FirstName": "Chris"}, {"FirstName": "Robert"}, {"FirstName": "Bob"} ]); { "acknowledged": true, ...
Read MoreMongoDB query to update array with another field?
To update an array with another field in MongoDB, use the $push operator along with $each to add multiple values at once. The $slice modifier can limit the array size. Syntax db.collection.update( {filter}, { $push: { arrayField: { $each: ["value1", "value2"], ...
Read MoreHow to delete element from an array in MongoDB?
To delete element from an array in MongoDB, use the $pull operator. This operator removes all instances of a specified value from an array field. Syntax db.collection.update( { query }, { $pull: { arrayField: valueToRemove } }, { multi: true } ); Create Sample Data Let us create a collection with documents − db.demo279.insertMany([ { id: [101, 103, 105, 110] }, { id: [107, 111, 110] } ]); { ...
Read MoreHow to create a performance system that count tags across a large dynamic dataset in MongoDB?
To create a performance system that counts tags across a large dynamic dataset in MongoDB, use indexes on array fields combined with aggregation pipelines and the explain() method to monitor query performance. Syntax // Create index on array field db.collection.createIndex({"arrayField": 1}); // Count tags with aggregation db.collection.aggregate([ { $unwind: "$arrayField" }, { $group: { _id: "$arrayField", count: { $sum: 1 } } } ]); // Monitor performance db.collection.find(query).explain("executionStats"); Sample Data Let us create a collection with documents containing subject tags − db.demo278.createIndex({"Subjects": ...
Read MoreMulti-key Indexing on an entire array with MongoDB?
Multi-key indexing in MongoDB allows you to index entire arrays and their nested elements efficiently. When you create an index on an array field, MongoDB automatically creates a multi-key index that indexes each array element separately. Syntax db.collection.createIndex({ "arrayField": 1 }) db.collection.find({ "arrayField": { "nestedField": "value" } }) Create Sample Data db.demo277.insertMany([ { "details": [{ "FirstName": "John" }] }, { "details": [{ "FirstName": "David" }] }, { "details": [{ "FirstName": "Chris" }] } ]); { ...
Read MoreSplit a document by its subdocuments in MongoDB
To split a document by its subdocuments, use $unwind in MongoDB. This operator deconstructs an array field from the input documents to output a document for each element. Syntax db.collection.aggregate([ { $unwind: "$arrayFieldName" } ]); Sample Data Let us create a collection with documents — db.demo276.insertOne({ "Name": "Chris", "Subjects": ["MySQL", "MongoDB"] }); { "acknowledged": true, "insertedId": ObjectId("5e48f953dd099650a5401a51") } Display all documents from a collection with the help ...
Read MoreMongoDB query to skip first 5 records and display only the last 5 of them
To skip records in MongoDB, use skip(). With that, to display only a specific number of records, use limit(). Syntax db.collection.find().skip(numberOfRecordsToSkip).limit(numberOfRecordsToDisplay); Create Sample Data Let us create a collection with documents ? db.demo275.insertMany([ {"Number": 10}, {"Number": 12}, {"Number": 6}, {"Number": 1}, {"Number": 5}, {"Number": 24}, {"Number": 8}, {"Number": 9}, {"Number": 19}, {"Number": ...
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