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To match documents whose _id is in an array stored as part of a subdocument, use the $in operator combined with distinct() to extract array values from the subdocument field. Syntax db.targetCollection.find({ "_id": { "$in": db.sourceCollection.distinct("arrayField.subField", {filter}) } }); Sample Data Create a collection with an array of subdocuments containing IDs ? db.demo568.insertOne({ _id: 101, details: [ { id: 101 }, ... Read More
To exclude specific fields from MongoDB query results, set the unwanted fields to 0 in the projection parameter of the find() method. This allows you to retrieve documents while hiding sensitive or unnecessary data. Syntax db.collectionName.find( { query }, { fieldToExclude1: 0, fieldToExclude2: 0 } ); Sample Data db.demo567.insertMany([ { "Name": "Chris", "Age": 21 }, { "Name": "David", "Age": 23 }, { "Name": "Bob", "Age": 22 }, { "Name": ... Read More
To group array items in MongoDB and count products with similar prices, use the $unwind operator to flatten the array, then $group by price and $sum to count occurrences. Syntax db.collection.aggregate([ { $unwind: "$arrayField" }, { $group: { "_id": "$arrayField.fieldToGroupBy", "count": { $sum: 1 } }}, { $sort: { "_id": 1 } } ]) Sample Data db.products.insertOne({ ... Read More
To access fields in a MongoDB document, use the find() method with optional field projection to specify which fields to return. You can access all fields or select specific ones using projection syntax. Syntax // Access all fields db.collection.find(query); // Access specific fields using projection db.collection.find(query, {field1: 1, field2: 1, _id: 0}); Sample Data db.demo565.insertMany([ { id: 101, Name: "David", CountryName: "US" ... Read More
To replace a single array value with a string in MongoDB, use the $set operator combined with the positional operator $. The positional operator identifies the array element that matches the query condition and allows you to update it. Syntax db.collection.updateMany( { "arrayField": "valueToMatch" }, { "$set": { "arrayField.$": "newValue" } } ); Sample Data db.demo564.insertOne({ "StudentName": ["Chris", "David", "Mike", "Sam"] }); { "acknowledged": true, "insertedId": ObjectId("5e90880a39cfeaaf0b97b576") } ... Read More
To get documents with a specific field value in MongoDB, use the find() method with a query filter. This allows you to retrieve only the documents that match your specified criteria. Syntax db.collection.find( { "field": "value" }, { "field1": 1, "field2": 1 } ) The first parameter is the query filter, and the second optional parameter is the projection to specify which fields to include or exclude. Sample Data db.demo563.insertMany([ { "Name": "Chris", "Age": 21, "isMarried": true }, ... Read More
To search for a field and then delete it in MongoDB, use $exists to find documents containing the field, then $unset to remove it. The $unset operator deletes a particular field from documents. Syntax db.collection.update( { "fieldName": { $exists: true } }, { $unset: { "fieldName": "" } }, { multi: true } ); Sample Data Let us create a collection with documents ? db.demo562.insertMany([ { "Name": "Chris", "Age": 21 }, { ... Read More
To randomize unique data with MongoDB and generate email addresses starting with "John", use Math.random() within JavaScript functions to create unique values for each document. Syntax db.collection.find().forEach(function(doc){ db.collection.update( {_id : doc._id}, {$set: {EmailId: 'John' + Math.random() * multiplier + '@domain.com'}} ) }) Sample Data First, create a collection with null EmailId fields ? db.demo561.insertMany([ {EmailId: null}, {EmailId: null}, ... Read More
Fetch data between two dates and with a specific value in MongoDB. Group and get the sum with count?
To fetch data between two dates and with a specific value in MongoDB, use $match to filter documents and $group to aggregate results. The $gte and $lte operators handle date range filtering. Syntax db.collection.aggregate([ { $match: { "fieldName": "specificValue", "dateField": { "$gte": ISODate("startDate"), ... Read More
To GROUP BY array of document to get count of repeated Age values, use the aggregation pipeline with $unwind to flatten the array and $group to count occurrences by Age. Syntax db.collection.aggregate([ { $unwind: "$arrayField" }, { $group: { _id: "$arrayField.groupingField", count: { $sum: 1 } } }, { $sort: { _id: 1 } } ]); Sample Data db.demo559.insertOne({ details: [ { Name: "Chris", Age: 21 }, ... Read More