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Articles on Trending Technologies
Technical articles with clear explanations and examples
Remove document whose value is matched with $eq from a MongoDB collection?
To remove documents from a MongoDB collection using the $eq operator, use the remove() method with a query that matches field values. The $eq operator explicitly matches documents where a field equals the specified value. Syntax db.collection.remove({ fieldName: { $eq: "value" } }); Create Sample Data Let us create a collection with documents − db.demo626.insertMany([ {id: 1, "Name": "Chris"}, {id: 2, "Name": "David"}, {id: 3, "Name": "Bob"}, {id: 4, "Name": "Mike"} ]); ...
Read MoreMongoDB - How can I see if all elements of a field are contained in a superset?
To check if all elements of an array field are contained within a superset in MongoDB, use the $not operator combined with $elemMatch and $nin. This ensures no array element exists outside the specified superset. Syntax db.collection.find({ "arrayField": { $not: { $elemMatch: { $nin: ["superset", "values", "here"] ...
Read MoreCan we search an array of objects in MongoDB?
Yes, you can search an array of objects in MongoDB using multiple approaches. The most common methods are direct field matching and the aggregation pipeline with $unwind. Syntax // Direct field matching db.collection.find({"arrayField.fieldName": "value"}) // Using aggregation with $unwind db.collection.aggregate([ {$unwind: "$arrayField"}, {$match: {"arrayField.fieldName": "value"}} ]) Sample Data db.demo623.insertOne({ _id: 1, details: [ { Name: "Chris" ...
Read MoreMongoDB Indexes - Is it possible to create both normal & compound at the same time?
Yes, you can create both normal (single field) and compound (multiple field) indexes simultaneously in MongoDB using the createIndex() method. MongoDB provides complete support for indexes on any field in a collection of documents. Syntax db.collection.createIndex({field1: 1, field2: 1, field3: 1}); Where 1 indicates ascending order and -1 indicates descending order. Example Let us create a compound index on multiple fields and insert sample documents ? db.demo622.createIndex({_id: 1, Name: 1, Age: 1}); { "createdCollectionAutomatically" : true, "numIndexesBefore" : 1, ...
Read MoreMongoDB Aggregate Second Element from Input Element?
To aggregate second element from input element in MongoDB, use mapReduce() with a counter variable in the scope. This method allows you to skip elements and select specific positions from a collection based on a divisor pattern. Syntax db.collection.mapReduce( function() { track++; if (track % div == 0) { emit(key, value); } }, ...
Read MoreAggregate by country, state and city in a MongoDB collection with multiple documents
Aggregation operations group values from multiple documents together, and can perform a variety of operations on the grouped data to return a single result. To aggregate by country, state and city in MongoDB, use the $group stage with $addToSet to organize data hierarchically. Syntax db.collection.aggregate([ { "$group": { "_id": { "Country": "$Country", "state": "$state" }, "City": { "$addToSet": { "City": "$City" ...
Read MoreMongoDB – Fix "Failed to convert from type String to type Date"?
To fix the "Failed to convert from type String to type Date" error in MongoDB, use $dateFromString in an aggregation pipeline. This operator converts a date/time string to a proper Date object that MongoDB can process. Syntax db.collection.aggregate([ { $project: { fieldName: { $dateFromString: { ...
Read MoreCan we work MongoDB findOne() with long type _id?
Yes, MongoDB's findOne() method works with NumberLong data type for _id fields. Use NumberLong() to wrap long integer values when storing and querying documents with numeric _id values that exceed JavaScript's safe integer range. Syntax db.collection.findOne({_id: NumberLong("longValue")}); Create Sample Data Let's create a collection with NumberLong _id values − db.demo618.insertMany([ {_id: NumberLong("6336366454"), Name: "Chris"}, {_id: NumberLong("6336366455"), Name: "David"}, {_id: NumberLong("6336366456"), Name: "Bob"} ]); { "acknowledged": true, "insertedIds": [ ...
Read MoreGroup query upon nested object in MongoDB?
To group documents by fields within nested objects in MongoDB, use dot notation with the $group aggregation stage. The dot notation allows you to access nested fields using the format "parentField.nestedField". Syntax db.collection.aggregate([ { $group: { _id: "$parentField.nestedField", count: { $sum: 1 } } ...
Read MoreHow can I aggregate collection and group by field count in MongoDB?
In MongoDB, use the $group stage with aggregate() to group documents by field values and count occurrences. The $sum operator with value 1 counts documents in each group. Syntax db.collection.aggregate([ { $group: { _id: "$fieldName", count: { $sum: 1 } } } ]); Sample Data ...
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