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Articles on Trending Technologies
Technical articles with clear explanations and examples
Handling optional/empty data in MongoDB?
To handle optional or empty data in MongoDB, use the $ne operator to exclude null values, the $exists operator to check field presence, and combine operators to filter various empty states like null, empty strings, or missing fields. Syntax // Exclude null values db.collection.find({ fieldName: { $ne: null } }) // Check if field exists db.collection.find({ fieldName: { $exists: true } }) // Exclude null AND missing fields db.collection.find({ fieldName: { $exists: true, $ne: null } }) Sample Data db.handlingAndEmptyDataDemo.insertMany([ { "StudentName": "John", "StudentCountryName": "" }, ...
Read MoreHow to loop through collections with a cursor in MongoDB?
In MongoDB, you can loop through collections with a cursor using the while loop with hasNext() and next() methods. A cursor is returned by the find() method and allows you to iterate through documents one by one. Syntax var cursor = db.collectionName.find(); while(cursor.hasNext()) { var document = cursor.next(); printjson(document); } Create Sample Data Let us create a collection with student documents ? db.loopThroughCollectionDemo.insertMany([ {"StudentName": "John", "StudentAge": 23}, {"StudentName": "Larry", "StudentAge": 21}, {"StudentName": ...
Read MoreHow to remove all documents from a collection except a single document in MongoDB?
To remove all documents from a collection except a single document in MongoDB, use deleteMany() or remove() with the $ne operator to exclude documents that match a specific condition. Syntax db.collection.deleteMany({ field: { $ne: value } }); // OR db.collection.remove({ field: { $ne: value } }); Create Sample Data db.removeAllDocumentsExceptOneDemo.insertMany([ {"StudentName": "Larry", "StudentAge": 21}, {"StudentName": "Mike", "StudentAge": 21, "StudentCountryName": "US"}, {"StudentName": "Chris", "StudentAge": 24, "StudentCountryName": "AUS"} ]); { "acknowledged": true, ...
Read MoreHow to compare field values in MongoDB?
To compare field values in MongoDB, you can use the $where operator for JavaScript-based comparisons or the $expr operator (recommended) for aggregation expression comparisons. Both methods allow you to compare fields within the same document. Syntax // Using $where (JavaScript evaluation) db.collection.find({ $where: "this.field1 > this.field2" }); // Using $expr (Aggregation expressions - recommended) db.collection.find({ $expr: { $gt: ["$field1", "$field2"] } }); Sample Data db.comparingFieldDemo.insertMany([ {"Value1": 30, "Value2": 40}, {"Value1": 60, "Value2": 70}, {"Value1": 160, "Value2": 190}, ...
Read MoreHow to find exact Array Match with values in different order using MongoDB?
To find exact array match with values in different order in MongoDB, use the $all operator combined with $size. The $all operator matches arrays containing all specified elements regardless of order, while $size ensures the exact array length. Syntax db.collection.find({ "arrayField": { "$size": exactLength, "$all": [value1, value2, value3] } }); Create Sample Data db.exactMatchArrayDemo.insertMany([ { "StudentName": "David", ...
Read MoreCan I query on a MongoDB index if my query contains the $or operator?
Yes, you can query on MongoDB indexes with the $or operator. MongoDB can effectively use separate indexes for each condition in the $or query, combining results through an OR stage in the execution plan. Syntax db.collection.find({ $or: [ { field1: value1 }, { field2: value2 } ]}).explain(); Create Sample Indexes First, create indexes on the fields you'll query ? db.indexOrQueryDemo.createIndex({"First": 1}); { "createdCollectionAutomatically": false, "numIndexesBefore": 2, "numIndexesAfter": 3, ...
Read MoreHow to retrieve the documents whose values end with a particular character in MongoDB?
To retrieve documents whose field values end with a particular character in MongoDB, use the $regex operator with the dollar sign ($) anchor to match the end of the string. Syntax db.collection.find({ fieldName: { $regex: "character$" } }); The $ symbol ensures the pattern matches only at the end of the string. Sample Data Let us create a collection with sample documents ? db.students.insertMany([ { "StudentName": "Adam", "StudentAge": 25, "StudentCountryName": "LAOS" }, { "StudentName": "Sam", "StudentAge": 24, "StudentCountryName": "ANGOLA" ...
Read MoreGet the first element in an array and return using MongoDB Aggregate?
To get the first element from an array using MongoDB aggregation, use the $arrayElemAt operator or combine $unwind with $first. The $arrayElemAt method is simpler and more efficient for this task. Syntax db.collection.aggregate([ { $project: { "fieldName": { $arrayElemAt: ["$arrayField", 0] } } } ]); Sample Data db.getFirstElementInArrayDemo.insertMany([ { ...
Read MoreHow to reduce MongoDB storage space after deleting large amount of data?
To reduce MongoDB storage space after deleting a large amount of data, you need to reclaim the freed disk space since MongoDB doesn't automatically release space after deletions. The database continues to use the same amount of disk space even after documents are removed. Syntax db.runCommand({ "compact": "collectionName" }) Or for the entire database: db.repairDatabase() Method 1: Using compact Command (Recommended) The compact command is the modern approach to reclaim space from a specific collection ? db.runCommand({ "compact": "users" }) { "ok" : 1, "bytesFreed" ...
Read MoreConcatenate strings from two fields into a third field in MongoDB?
To concatenate strings from two fields into a third field in MongoDB, use the $concat operator within an aggregation pipeline with $project stage. Syntax db.collection.aggregate([ { $project: { "newFieldName": { $concat: [ "$field1", "delimiter", "$field2" ] } } } ]); Sample Data db.concatenateStringsDemo.insertMany([ {"StudentFirstName": "John", "StudentLastName": "Doe"}, {"StudentFirstName": "John", "StudentLastName": "Smith"}, {"StudentFirstName": "Carol", "StudentLastName": "Taylor"}, {"StudentFirstName": "David", "StudentLastName": "Miller"}, {"StudentFirstName": "James", "StudentLastName": "Williams"} ]); { ...
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