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Articles by AmitDiwan
Page 592 of 840
MongoDB - How to check for equality in collection and in embedded document?
To check for equality between a field in the main collection and a field in an embedded document, use the $where operator with JavaScript expressions. This allows you to compare values across different nesting levels within the same document. Syntax db.collection.find({ $where: 'this.fieldName === this.embeddedDoc.fieldName' }); Sample Data db.demo292.insertMany([ { "FirstName": "Chris", "LastName": "Brown", "Friend": { ...
Read MoreMongoDB - How to get the sum of two columns and save it to another column?
To get the sum of two columns and save it to another column in MongoDB, use the $add operator within an aggregation pipeline with the $project stage. Syntax db.collection.aggregate([ { $project: { field1: "$field1", field2: "$field2", sumField: { $add: ["$field1", "$field2"] } ...
Read MoreMongoDB query for exact match
For exact match queries in MongoDB, you can combine the $exists operator with field conditions to ensure precise matching, especially when dealing with fields that could contain either single values or arrays. Syntax db.collection.find({ $and: [ {"field.0": {$exists: false}}, {"field": "exactValue"} ] }); Sample Data db.demo290.insertMany([ {"ListOfName": "Chris"}, {"ListOfName": ["Chris", "David"]} ]); { "acknowledged": ...
Read MoreMake an array of multiple arrays in MongoDB?
To make an array of multiple arrays in MongoDB, use $unwind in the aggregation pipeline to deconstruct array fields. This operation creates separate documents for each array element, effectively flattening multiple arrays into individual elements. Syntax db.collection.aggregate([ { $unwind: "$arrayField" } ]); Sample Data db.demo289.insertMany([ {"Section": ["A", "B", "E"], "Name": "Chris"}, {"Section": ["C", "D", "B"], "Name": "David"} ]); { "acknowledged": true, "insertedIds": [ ...
Read MoreImplement MongoDB $push in embedded document array?
To implement MongoDB $push in an embedded document array, use the $push operator to add new documents to an existing array field within a document. Syntax db.collection.update( { "field": "value" }, { $push: { "arrayField": { "newDocument": "value" } } } ); Sample Data Let us create a collection with documents − db.demo288.insertOne({ "Name": "Chris", "details": [ {"CountryName": "US", "Marks": 78}, ...
Read MoreMin and max values of an array in MongoDB?
To find the minimum and maximum values from array elements in MongoDB, use the $min and $max operators within an aggregation pipeline. These operators work on array fields to extract the smallest and largest values respectively. Syntax db.collection.aggregate([ { $project: { "minField": { $min: "$arrayField.property" }, "maxField": { $max: "$arrayField.property" } } ...
Read MoreWhat is the BSON query for the command 'show dbs' (list of databases) in MongoDB?
The BSON equivalent of the show dbs command in MongoDB is the listDatabases administrative command. This command must be run against the admin database to retrieve information about all databases on the MongoDB instance. Syntax db.runCommand({ listDatabases: 1 }) Example First, switch to the admin database ? use admin switched to db admin Now, run the listDatabases command ? db.runCommand({ listDatabases: 1 }) This will produce the following output ? { "databases": [ ...
Read MoreMongoDB query to limit subdocuments having the given fields of the 'projection'
To limit subdocuments having specific fields during projection in MongoDB, use the aggregation pipeline with $match, $unwind, and $project stages to filter and reshape the data. Syntax db.collection.aggregate([ { $match: { "arrayField.targetField": { $exists: 1 } } }, { $unwind: "$arrayField" }, { $match: { "arrayField.targetField": { $exists: 1 } } }, { $project: { "newField": "$arrayField.targetField", "_id": 0 } } ]); Sample Data db.demo285.insertOne({ details: [ ...
Read MoreExport specified field of a collection in mongodb / mongodump to file?
To export specified fields from a MongoDB collection, use the mongoexport command with the -f parameter to specify which fields to export. This utility allows you to export data in various formats including CSV and JSON. Syntax mongoexport -d yourDatabaseName -c yourCollectionName -f yourFieldName --type=csv -o yourFileLocation/FileName Sample Data Let us create a collection with sample documents ? db.demo284.insertMany([ {"FirstName": "Chris"}, {"FirstName": "Robert"}, {"FirstName": "Bob"} ]); { "acknowledged": true, ...
Read MoreMongoDB query to update array with another field?
To update an array with another field in MongoDB, use the $push operator along with $each to add multiple values at once. The $slice modifier can limit the array size. Syntax db.collection.update( {filter}, { $push: { arrayField: { $each: ["value1", "value2"], ...
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