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Articles on Trending Technologies
Technical articles with clear explanations and examples
MongoDB, finding all documents where property id equals to record id?
To find all documents where a property id equals the record's _id in MongoDB, use the $where operator with a JavaScript function that compares the field values after converting them to strings. Syntax db.collection.find({ $where: function(){ return this._id.toString() == this.fieldName.toString(); } }); Sample Data db.demo69.insertMany([ { "_id": ObjectId("507c7f79bcf86cd7994f6c0e"), "Details": { ...
Read MoreMongoDB aggregate query to sort
The $sort stage in MongoDB aggregation pipeline sorts documents by one or more fields. Use 1 for ascending order and -1 for descending order. You can combine it with other stages like $match to filter and sort results. Syntax db.collection.aggregate([ { $match: { field: value } }, { $sort: { field: 1 } } // 1 for ascending, -1 for descending ]); Sample Data db.demo67.insertMany([ { "StudentAge": 23 }, { "StudentAge": 21 }, ...
Read MoreHow to get the index of an array element in older versions on MongoDB?
To get the index of an array element in older versions of MongoDB, use the $indexOfArray aggregation operator. This operator returns the position (0-based index) of the first occurrence of a specified value in an array, or -1 if the value is not found. Syntax db.collection.aggregate([ { $project: { fieldName: { $indexOfArray: ["$arrayField", "searchValue"] } } } ]); Sample ...
Read MoreMongoDB aggregation to sum product price with similar IDs
To sum product prices with similar IDs in MongoDB, use the $group stage in aggregation pipeline with $sum operator. This groups documents by a specified field and calculates the total for each group. Syntax db.collection.aggregate([ { $group: { _id: "$groupingField", totalFieldName: { $sum: "$fieldToSum" } } } ]); ...
Read MoreHow to properly use 'exist' function in MongoDB like in SQL?
To check for existence of a record in MongoDB (similar to SQL's EXISTS function), use findOne() method. This returns the first matching document if it exists, or null if no document matches the query criteria. Syntax db.collection.findOne({ field: "value" }) Sample Data db.existsAlternateDemo.insertMany([ { "StudentName": "Chris" }, { "StudentName": "Chris", "StudentAge": 21 }, { "StudentName": "Chris", "StudentAge": 22, "StudentCountryName": "US" } ]); { "acknowledged": true, "insertedIds": [ ...
Read MoreInsert in MongoDB without duplicates
To insert records in MongoDB and avoid duplicates, create a unique index on the field that should not contain duplicate values. When you attempt to insert a document with a duplicate value, MongoDB will reject the operation with an error. Syntax db.collection.createIndex({"fieldName": 1}, { unique: true }); db.collection.insert({"fieldName": "value"}); Example Let's create a unique index on the StudentFirstName field and attempt to insert duplicate records ? Step 1: Create Unique Index db.insertWithoutDuplicateDemo.createIndex({"StudentFirstName":1}, { unique: true }); { "createdCollectionAutomatically" : true, "numIndexesBefore" : ...
Read MoreApply a condition inside subset in MongoDB Aggregation?
To apply a condition inside subset in MongoDB aggregation, use $setIsSubset. This operator checks whether a specified set is a subset of another set, returning true if all elements exist in the target array. Syntax { $setIsSubset: [, ] } Sample Data db.subsetDemo.insertMany([ { "StudentName": "Chris", "StudentFavouriteSubject": ["Java", "Python"] }, { "StudentName": "Chris", ...
Read MoreGetting MongoDB results from the previous month
To get MongoDB results from the previous month, first get the current date and subtract one month from it. This creates a date boundary to filter records that fall within the previous month period. Syntax var previousMonth = new Date(); previousMonth.setMonth(previousMonth.getMonth() - 1); db.collection.find({dateField: {$gte: previousMonth}}); Sample Data db.findOneMonthAgoData.insertMany([ {"CustomerName": "Chris", "PurchaseDate": new ISODate("2019-12-26")}, {"CustomerName": "David", "PurchaseDate": new ISODate("2019-11-26")}, {"CustomerName": "Bob", "PurchaseDate": new ISODate("2020-11-26")} ]); { "acknowledged": true, "insertedIds": [ ...
Read MoreHow can I aggregate nested documents in MongoDB?
To aggregate nested documents in MongoDB, you can use the aggregation pipeline with operators like $unwind and $group. The $unwind operator flattens array fields, allowing you to process individual elements within nested structures. Syntax db.collection.aggregate([ { $unwind: "$arrayField" }, { $unwind: "$arrayField.nestedArray" }, { $group: { _id: null, result: { $operation: "$arrayField.nestedArray.field" } } } ]); Sample Data db.aggregateDemo.insertMany([ { "ProductInformation": [ ...
Read MoreHow to add a column in MongoDB collection?
To add a column (field) in MongoDB, you need to update the collection using the $set operator. Since MongoDB is schema-less, adding a new field means updating existing documents to include the new field. Syntax db.collection.updateMany({}, {$set: {"newColumnName": "value"}}); Sample Data Let us create a collection with some sample documents ? db.addColumnDemo.insertMany([ {"StudentId": 101, "StudentName": "Chris"}, {"StudentId": 102, "StudentName": "Robert"}, {"StudentId": 103, "StudentName": "David"} ]); { "acknowledged": true, "insertedIds": ...
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