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To implement MongoDB $push in an embedded document array, use the $push operator to add new documents to an existing array field within a document. Syntax db.collection.update( { "field": "value" }, { $push: { "arrayField": { "newDocument": "value" } } } ); Sample Data Let us create a collection with documents − db.demo288.insertOne({ "Name": "Chris", "details": [ {"CountryName": "US", "Marks": 78}, ... Read More
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 More
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 More
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 More
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 More
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 More
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 More
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 More
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 More
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 More