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To use custom variables while updating MongoDB documents, first declare a variable with var, then reference it in your update() operation. This allows for dynamic updates and better code reusability. Syntax var variableName = yourValue; db.collectionName.update( { filter }, { $set: { fieldName: variableName } } ); Create Sample Data db.demo600.insertMany([ { id: 1, Name: "Robert" }, { id: 2, Name: "Mike" }, { id: 3, Name: "Sam" } ]); ... Read More
To subtract values from document field values in MongoDB, use the $subtract operator within the aggregation pipeline. This operator performs arithmetic subtraction between numeric field values or expressions. Syntax db.collection.aggregate([ { $project: { newField: { $subtract: ["$field1", "$field2"] } ... Read More
To find which document contains a specific string, use $regex along with find(). The regex operator performs pattern matching to locate documents containing the specified text substring. Syntax db.collection.find({ fieldName: { $regex: /pattern/flags } }); Sample Data db.demo597.insertMany([ { "Name": "John Doe" }, { "Name": "John Smith" }, { "Name": "Chris Brown" }, { "Name": "Adam Smith" } ]); { "acknowledged": true, ... Read More
To update a nested document in MongoDB, use the $ positional operator with the $set operator. The $ operator identifies the array element that matches the query condition and allows you to update specific fields within that element. Syntax db.collection.update( {"arrayName.field": "matchValue"}, { $set: { "arrayName.$.field": "newValue" } } ); Create Sample Data Let us create a collection with documents − db.demo595.insertOne({ "Information": [ { "_id": new ObjectId(), "Name": "Chris" }, ... Read More
To limit the returning values of a field in MongoDB, use the $slice operator in the projection parameter of the find() method. This is particularly useful for limiting array elements returned in query results. Syntax db.collection.find( {}, { "arrayField": { "$slice": numberOfElements } } ); Sample Data db.demo594.insertOne({ id: 1, details: [ { Name: "Chris", Age: 21 }, { Name: "Bob", ... Read More
To fetch specific multiple documents in MongoDB, use the $in operator to match documents where a field value equals any value in a specified array. Syntax db.collection.find({ "field": { $in: [value1, value2, value3, ...] } }); Sample Data Let us create a collection with documents − db.demo593.insertMany([ { id: 1, "Name": "Chris" }, { id: 2, "Name": "John" }, { id: 3, "Name": "Bob" }, { id: 4, "Name": "Sam" } ]); ... Read More
To match documents that contain an array field, use the $elemMatch operator. This operator matches documents where at least one array element meets all specified criteria within a single element. Syntax db.collection.find({ "arrayField": { "$elemMatch": { "field1": "value1", "field2": "value2" } } }); Sample Data Let ... Read More
To find documents where billing address equals delivery address in MongoDB, use the $where operator with JavaScript expressions to compare field values within the same document. Syntax db.collection.find({ $where: "this.field1 == this.field2" }); Sample Data db.demo589.insertMany([ {deliveryAddress: "US", billingAddress: "UK"}, {deliveryAddress: "US", billingAddress: "US"}, {deliveryAddress: "US", billingAddress: "AUS"}, {deliveryAddress: "UK", billingAddress: "US"} ]); { "acknowledged" : true, "insertedIds" : [ ... Read More
To gather unique array items from a MongoDB collection, use the distinct() method. This method returns an array of unique values for a specified field, automatically removing duplicates. Syntax db.collection.distinct("fieldName") Sample Data Let us create a collection with documents ? db.demo588.insertOne({ "CountryName": ["US", "AUS", "UK", "US", "UK", "AUS"] }); { "acknowledged": true, "insertedId": ObjectId("5e92bbd2fd2d90c177b5bccb") } Display all documents from the collection ? db.demo588.find().pretty(); { "_id": ObjectId("5e92bbd2fd2d90c177b5bccb"), ... Read More
To append subdocuments in MongoDB, use the $push operator with the update() method. This operator adds new subdocuments to an existing array field without removing existing elements. Syntax db.collection.update( { "field": "matchValue" }, { "$push": { "arrayField": { subdocumentData } } } ); Sample Data Let us create a collection with documents − db.demo587.insertMany([ { "id": 101, "details": [{ Name: "Chris", Age: 21, Marks: 57 }] }, { "id": 102, "details": [{ Name: "Bob", Age: 22, ... Read More