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Articles on Trending Technologies
Technical articles with clear explanations and examples
How can I count the documents in an array based on the value of a specific field?
To count documents in an array based on the value of a specific field, use the $unwind operator to flatten the array, followed by $match to filter, and $group to count the matching elements. Syntax db.collection.aggregate([ { $unwind: "$arrayField" }, { $match: { "arrayField.fieldName": "targetValue" } }, { $group: { _id: null, count: { $sum: 1 } }} ]); Sample Data ...
Read MoreSet filtering conditions for nested array in MongoDB
To set filtering conditions for nested arrays in MongoDB, use the $filter operator combined with $anyElementTrue and $map in an aggregation pipeline. This approach allows you to filter outer array elements based on conditions within deeply nested arrays. Syntax db.collection.aggregate([ { $addFields: { "arrayField": { $filter: { ...
Read MoreHow to count a cursor's iteration in MongoDB?
To count a cursor's iteration in MongoDB, you need to use custom logic with a while loop along with a find() cursor. This allows you to iterate through documents and count specific conditions during traversal. Syntax var cursor = db.collection.find(); var count = 0; while (cursor.hasNext()) { var document = cursor.next(); // Apply your counting logic here if (condition) { count++; } } Sample Data db.demo724.insertMany([ ...
Read MoreGet count of array elements from a specific field in MongoDB documents?
To count array elements from a specific field in MongoDB, use the $size operator within an aggregation pipeline. This operator returns the number of elements in an array field for each document. Syntax db.collection.aggregate([ { $project: { count: { $size: "$arrayFieldName" } } } ]); Sample Data db.demo723.insertMany([ {"Subject": ["MySQL", "MongoDB"]}, {"Subject": ["C"]}, {"Subject": ["C++", "Java", "Python"]} ]); { "acknowledged": true, "insertedIds": [ ...
Read MoreCount by multiple fields with MongoDB aggregation
To count by multiple fields in MongoDB, use the $facet operator combined with $group and $sum. The $facet processes multiple aggregation pipelines within a single stage on the same set of input documents. Syntax db.collection.aggregate([ { $facet: { "pipeline1": [ /* aggregation stages */ ], "pipeline2": [ /* aggregation stages */ ] } ...
Read MoreUpdate all the values of a field with a specific string in MongoDB?
To update all the values of a field with a specific string in MongoDB, use the update() method with an empty filter and the multi: true option to affect all documents in the collection. Syntax db.collection.update( {}, { $set: { "fieldName": "newValue" } }, { multi: true } ); Sample Data db.demo720.insertMany([ { "SubjectName": "MySQL" }, { "SubjectName": "Java" }, { "SubjectName": "C" }, { ...
Read MoreMongoDB query to add a new field and concatenate the price result divided by a specific number in it
To add a new field and concatenate price results divided by a specific number in MongoDB, use the $addFields stage with $reduce and $map operators to process array values and combine them into a single string. Syntax db.collection.aggregate([ { $addFields: { newField: { $reduce: { ...
Read MoreHow can I sort documents in MongoDB 4 and display only a single field?
To sort documents in MongoDB and display only a single field, use the sort() method combined with projection. The sort() method orders documents, while projection controls which fields appear in the result. Syntax db.collection.find({}, {fieldName: 1}).sort({fieldName: 1}); Where 1 means ascending order and -1 means descending order. Sample Data db.demo611.insertMany([ {"Name": "Chris"}, {"Name": "Adam"}, {"Name": "John"}, {"Name": "Bob"} ]); { "acknowledged": true, "insertedIds": [ ...
Read MoreHow to add together a subset of elements of an array in MongoDB aggregation?
To add together a subset of elements of an array in MongoDB aggregation, use the $slice operator combined with $sum to select and sum specific array elements based on position or range. Syntax db.collection.aggregate([ { $project: { subsetSum: { $sum: { ...
Read MoreMongoDB query to remove entire array from collection?
To remove an entire array field from all documents in a MongoDB collection, use the $unset operator. This completely removes the specified field from the documents. Syntax db.collection.updateMany( {}, { $unset: { "arrayFieldName": "" } } ); Sample Data Let us create a collection with documents containing array fields ? db.demo609.insertMany([ { "ListOfSubject": ["MySQL", "MongoDB"] }, { "ListOfSubject": ["Java"] } ]); { "acknowledged": true, "insertedIds": [ ...
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