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Articles on Trending Technologies
Technical articles with clear explanations and examples
How to work with variables in MongoDB query
To use variables in MongoDB queries, work with the var keyword to declare variables and reference them in your queries. This approach makes queries more flexible and reusable. Syntax var variableName = "value"; db.collection.find({"field": variableName}); Sample Data Let us create a collection with documents ? db.demo107.insertMany([ {"Name": "Chris"}, {"Name": "Bob"}, {"Name": "David"} ]); { "acknowledged": true, "insertedIds": [ ObjectId("5e2ee1b19fd5fd66da214471"), ...
Read MoreInsert array where element does not exist else update it (with multiple conditions)?
To insert array elements when they don't exist or update them when they do using multiple conditions, use bulkWrite() with multiple updateOne operations. This allows conditional updates and insertions in a single atomic operation. Syntax db.collection.bulkWrite([ { "updateOne": { "filter": { "field": "value", "array": { "$elemMatch": { conditions } } }, "update": { "$set": { "array.$.field": "newValue" } } ...
Read MoreImplement $dateToString on array items with MongoDB
To implement $dateToString on array items in MongoDB, use the $map operator inside an aggregation pipeline to transform date fields within array elements into formatted strings. Syntax db.collection.aggregate([ { $project: { "arrayField": { $map: { "input": "$arrayField", ...
Read MoreMongoDB Aggregate JSON array field for the matching field of other collection?
To aggregate JSON array field for matching fields from another collection in MongoDB, use $lookup combined with $unwind to join collections based on array elements, then reconstruct the result using $group. Syntax db.collection1.aggregate([ { $unwind: "$arrayField" }, { $lookup: { from: "collection2", localField: "arrayField.joinField", foreignField: "_id", as: "matchedData" }}, ...
Read MoreMongoDB query to implement nor query to fetch documents except a specific document
To fetch documents except a specific document, use the $nor operator in MongoDB. The $nor operator performs a logical NOR operation, returning documents that do not match any of the conditions in the array. Syntax db.collection.find({ $nor: [ { field1: value1 }, { field2: value2 } ] }); Sample Data Let's create a collection with sample documents ? db.demo100.insertMany([ { "Name": "Chris", "Age": 21 ...
Read MoreHow to group nested fields in MongoDB aggregation with count value in array?
To group nested fields in MongoDB aggregation with count values from arrays, use the $objectToArray operator to convert nested objects into key-value pairs, then use $unwind and $group to aggregate the count values. Syntax db.collection.aggregate([ { $project: { fieldName: { $objectToArray: "$nestedObject" } } }, { $unwind: "$fieldName" }, { $group: { _id: "$fieldName.k", count: { $sum: "$fieldName.v.countField" } } } ]) Sample Data db.demo99.insertMany([ { "Details": { ...
Read MoreIncrement a property value of an element in array object with MongoDB
To increment a property value of an element in a MongoDB array, use the $inc operator combined with the $ positional operator. The $ operator identifies the matched array element, while $inc increases the specified field by a given value. Syntax db.collection.update( { "arrayField.property": "matchValue" }, { $inc: { "arrayField.$.targetProperty": incrementValue } } ); Sample Data Let us create a collection with student details ? db.demo97.insertOne({ "Details": [ { ...
Read MoreFind sum of fields inside array in MongoDB?
To find sum of fields inside array in MongoDB, use the $sum operator with the aggregation pipeline. The $sum operator can directly reference array fields using dot notation to calculate the total of numeric values. Syntax db.collection.aggregate([ { $project: { "fieldName": 1, "totalSum": { $sum: ...
Read MoreHow to update array with multiple conditions in MongoDB
To update array with multiple conditions in MongoDB, use $elemMatch to match array elements with specific criteria, combined with $push and the positional operator $ to add new elements to the matched array element. Syntax db.collection.updateOne( { "arrayField": { "$elemMatch": { "field1": "value1", "field2": "value2" } } }, { "$push": { "arrayField.$.targetField": newValue } } ); Sample Data db.demo94.insertOne({ "Details": [ { ...
Read MoreHow to convert date to timestamp in MongoDB
To convert date to timestamp in MongoDB, use the $toLong operator within an aggregation pipeline. This converts an ISODate object to its Unix timestamp representation in milliseconds. Syntax db.collection.aggregate([ { $addFields: { "timestampField": { $toLong: "$dateField" } } } ]); Sample Data db.demo93.insertMany([ {"UserName": "Chris", "ArrivalDate": new ISODate("2020-10-01")}, {"UserName": ...
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