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Big Data Analytics Articles
Page 4 of 135
How 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": [ ...
Read MoreGetting unique values within two arrays in one MongoDB document
To get unique values within two arrays in a MongoDB document, use the $setUnion operator in the aggregation pipeline. The $setUnion takes two or more arrays and returns an array containing the unique elements that appear in any input array. Syntax db.collection.aggregate([ { $project: { uniqueArray: { $setUnion: ["$array1", "$array2"] } } } ]) Sample Data Let us ...
Read MoreMongoDB query to update the nested document?
To update a nested document in MongoDB, use the update() method with dot notation to specify the path to the nested field. This allows you to modify deeply embedded values without affecting the parent document structure. Syntax db.collection.update( { "filterField": "value" }, { $set: { "parentField.nestedField.targetField": "newValue" } } ); Sample Data Let us create a collection with a nested document structure ? db.demo607.insertOne({ id: 1, "Info1": { ...
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