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Articles on Trending Technologies
Technical articles with clear explanations and examples
How to get max values for distinct elements in MongoDB
To get max values for distinct elements in MongoDB, use the $group operator with $max to find the highest value for each distinct element. This aggregation pipeline groups documents by a field and returns the maximum value within each group. Syntax db.collection.aggregate([ { $group: { _id: "$fieldName", maxValue: { $max: "$valueField" } } ...
Read MoreMongoDB query to update each field of documents in collection with a formula?
To update each field of documents in collection with a formula in MongoDB, use the $mul operator with the positional all operator $[] to apply mathematical operations across all array elements. Syntax db.collection.update( {}, { $mul: { "arrayField.$[].fieldName": formulaValue } }, { multi: true } ); Sample Data db.demo749.insertOne({ "details": [ {"id": 1, "a": 10}, {"id": 2, "a": 5}, ...
Read MoreWhat is the maximum size of a document in MongoDB?
The maximum size of a document in MongoDB is 16 MB (16, 777, 216 bytes). This limit ensures efficient memory usage and prevents documents from consuming excessive resources during operations. Syntax // Document structure with size limit { field1: "value1", field2: "value2", // ... additional fields // Total document size ≤ 16 MB } Sample Data Let us create a collection with sample documents ? db.demo748.insertMany([ {_id: 101, Name: "Chris", Age: 21}, ...
Read MorePushing 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" } ]); ...
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