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The $match operator filters documents to pass only those that match specified conditions to the next pipeline stage. The $project operator reshapes documents by including, excluding, or adding new fields before passing them to the next stage. Syntax db.collection.aggregate([ { $match: { field: value } }, { $project: { field1: 1, field2: 0, newField: "$existingField" } } ]); Sample Data Let us create a collection with student documents ? db.demo545.insertMany([ { "Name": ... Read More
In MongoDB, the NumberLong() wrapper handles 64-bit integers that exceed JavaScript's safe integer range. To print NumberLong values, use the toString() method or direct printing to display the value properly. Syntax var variableName = NumberLong("longNumber"); variableName.toString(); // Or direct printing print(variableName); Example 1: Using toString() Method Create a NumberLong variable and display it using toString() ? var number = NumberLong("231231231231121231"); number.toString(); NumberLong("231231231231121231") Example 2: Another NumberLong Value Display a different NumberLong value ? var anotherNumber = NumberLong("765765765765567576"); anotherNumber.toString(); NumberLong("765765765765567576") ... Read More
To aggregate data by hour and calculate the average in MongoDB, use the aggregate() method with $group stage. The $hour operator extracts the hour from a date field, and $avg calculates the average value. Syntax db.collection.aggregate([ { $group: { "_id": { "$hour": "$dateField" }, "fieldName": { "$avg": "$numericField" } } ... Read More
To find a document that matches the same array elements in MongoDB, use the $all operator combined with $size. The $all operator selects documents where the array field contains all specified elements, while $size ensures the array has exactly the required number of elements. Syntax db.collection.find({ "arrayField": { $all: ["element1", "element2", "element3"], $size: numberOfElements } }); Sample Data db.demo543.insertMany([ {id: 101, subject: ... Read More
To add a boolean field true to returned objects when a specified value exists in an array (and false for NULL or missing values), use the $ifNull operator with $setIntersection and $size to check array membership. Syntax db.collection.aggregate([ { "$project": { "fieldName": { "$eq": [ ... Read More
To select documents grouped by field in MongoDB, use the $group stage in an aggregation pipeline along with $project to reshape the output. The $group stage groups documents by specified field values and accumulates data using operators like $push. Syntax db.collection.aggregate([ { "$group": { "_id": { "field1": "$field1", "field2": "$field2" }, "groupedData": { "$push": { "field3": "$field3" } } ... Read More
To remove a subdocument from a document in MongoDB, use the $pull operator along with update(). The $pull operator removes all array elements that match a specified condition. Syntax db.collection.update( { "matchField": "value" }, { $pull: { "arrayField": { "field": "condition" } } } ); Create Sample Data db.demo538.insertOne({ id: 101, "details": { anotherDetails: [ { ... Read More
To group documents with multiple fields and count duplicate combinations in MongoDB, use the aggregation framework with $project and $group stages. The $cond operator helps normalize field values for consistent grouping regardless of field order. Syntax db.collection.aggregate([ { $project: { field1: { $cond: { if: condition, then: value1, else: value2 } }, field2: { $cond: { if: condition, then: value1, else: ... Read More
To delete array values from a document in MongoDB, use the $pull operator. The $pull operator removes from an existing array all instances of a value or values that match a specified condition. Syntax db.collection.update( { "matchCondition": "value" }, { $pull: { "arrayField": "valueToRemove" } } ); Create Sample Data Let us first create a collection with documents − db.demo535.insertOne({ "studentId": "101", "studentName": "Chris", "ListOfMailIds": [ ... Read More
The $addToSet operator adds values to an array unless the value is already present, in which case $addToSet does nothing to that array. When used with $group in aggregation, it creates a unique set of values from a field across multiple documents. Syntax db.collection.aggregate([ { $group: { _id: groupingField, arrayField: { $addToSet: "$fieldName" } ... Read More