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Articles on Trending Technologies
Technical articles with clear explanations and examples
Using $redact in MongoDB aggregate?
The $redact stage in MongoDB aggregation pipeline restricts document contents based on information stored within the documents themselves. It uses conditional logic to decide whether to keep, prune, or descend into document fields. Syntax db.collection.aggregate([ { $redact: { $cond: { if: , ...
Read MoreImplement match and project in MongoDB aggregate
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 MoreHow to print NumberLong value in MongoDB?
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 MoreNeed to aggregate by hour and $avg in MongoDB
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 MoreFind document that matches same array elements in MongoDB?
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 MoreAdd a boolean field true to returned objects, when a specified value is in array. For NULLnor other values, set false.
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 MoreSelect documents grouped by field in MongoDB?
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 MoreMongoDB query to remove subdocument from document?
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 MoreGroup with multiple fields and get the count of duplicate field values grouped together innMongoDB
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 MoreHow do I delete array value from a document in MongoDB?
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": [ ...
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