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Big Data Analytics Articles
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Pushing values into array with multi field set to TRUE?
To push values into arrays across multiple documents in MongoDB, use the $push operator with update() and set the multi field to true. This allows updating all matching documents in a single operation. Syntax db.collection.update( {filter}, { $push: { arrayField: "value" } }, { multi: true } ); Sample Data db.demo747.insertMany([ { "CountryName": ["US", "IND"] }, { "CountryName": ["UK", "US"] }, { "CountryName": ["UK", "IND"] } ]); ...
Read MoreFind posts that are older than current date in MongoDB?
To find posts older than current date in MongoDB, use the $lte operator with new Date() to compare document dates against the current system date. Syntax db.collection.find({ dateField: { $lte: new Date() } }); Sample Data Let us create a collection with documents containing different due dates ? db.demo746.insertMany([ { DueDate: new Date("2020-01-10") }, { DueDate: new Date("2020-10-10") }, { DueDate: new Date("2020-03-05") }, { DueDate: new Date("2020-05-04") } ]); ...
Read MoreConcatenate with condition in MongoDB?
To concatenate with condition in MongoDB, use $cond with $concat in an aggregation pipeline. This allows you to perform string concatenation based on specific conditions and filter results accordingly. Syntax db.collection.aggregate([ { "$redact": { "$cond": [ { "$eq": [{ "$concat": ["$field1", "$field2"] }, "targetValue"] }, ...
Read MoreHow to find a certain element in the MongoDB embedded document?
To find a certain element in a MongoDB embedded document, use the aggregation pipeline with $unwind to flatten the array, $match to filter specific elements, and $project to select desired fields. Syntax db.collection.aggregate([ { $unwind: "$arrayField" }, { $match: { "arrayField.field": "value" } }, { $project: { "arrayField.desiredField": 1 } } ]) Sample Data db.demo744.insertOne({ studentInformation: [ { ...
Read MoreHow can I extract entire documents based on how they compare with their whole collection?
To extract entire documents based on how they compare with their whole collection in MongoDB, use the $$ROOT variable within an aggregation pipeline. This allows you to preserve complete documents while performing grouping and comparison operations. Syntax db.collection.aggregate([ { $project: { "field1": "$field1", "field2": "$field2", "document": "$$ROOT" ...
Read MoreI can print out each element of an array by iterating through all values, but can't get a specific element in MongoDB
In MongoDB, you can fetch specific elements from arrays using projection operators like $elemMatch or array indexing, which is more efficient than iterating through all values with forEach(). Syntax // Using array index db.collection.find({}, {"arrayField.index": 1}); // Using $elemMatch db.collection.find({}, {arrayField: {$elemMatch: {field: "value"}}}); Sample Data db.demo742.insertOne({ "userDetails": [ { "userName": "Robert", "CountryName": "UK" ...
Read MoreUpdating MongoDB collection for _id?
To update a document in MongoDB using its _id field, use the $set operator within an update operation. The _id field serves as the unique identifier for each document in a collection. Syntax db.collection.update( { _id: ObjectId("document_id") }, { $set: { field: "newValue" } } ); Sample Data Let us create a collection with sample documents ‒ db.demo741.insertMany([ { SubjectName: "MySQL" }, { SubjectName: "C" }, { SubjectName: "Java" } ]); ...
Read MoreHow to display only the keys from nested MongoDB documents?
To display only the keys from nested MongoDB documents, use the aggregation pipeline with $reduce, $map, and $objectToArray operators to extract and combine all field names from nested objects or arrays. Syntax db.collection.aggregate([ { $project: { keys: { $reduce: { ...
Read MoreHow to push value with for loop in MongoDB?
To push values with a for loop in MongoDB, use the save() method inside a for loop to insert multiple documents iteratively. This approach is useful when you need to create many similar documents programmatically. Syntax for(var i = start; i < end; i++) { db.collection.save({field1: "value", field2: "value"}); } Example Create 6 documents using a for loop ? for(var v = 1; v < 7; v++) { db.demo739.save({Name: "Chris", SubjectName: "MongoDB"}); } WriteResult({ "nInserted" : 1 }) Verify ...
Read MoreHow to order by timestamp (descending order) in MongoDB
To order by timestamp in descending order in MongoDB, use the sort() method with the timestamp field set to -1. This arranges documents from newest to oldest timestamp. Syntax db.collection.find().sort({"timestamp": -1}); Create Sample Data Let us create a collection with timestamp documents ? db.demo737.insertMany([ {"timestamp": new ISODate("2020-04-01")}, {"timestamp": new ISODate("2020-10-31")}, {"timestamp": new ISODate("2020-05-02")} ]); { "acknowledged": true, "insertedIds": [ ObjectId("5ead682157bb72a10bcf065c"), ...
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