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Big Data Analytics Articles
Page 7 of 135
Apply the Group Accumulator Operator $first on the system variable ROOT to return reference to the root document?
The $first group accumulator operator combined with the $$ROOT system variable returns a reference to the first complete document encountered in each group. The $$ROOT variable references the entire root document being processed in the aggregation pipeline. Syntax db.collection.aggregate([ { $group: { _id: "$groupingField", firstDocument: { $first: "$$ROOT" } } ...
Read MoreHow do I order a list and add position to its items in MongoDB?
To order a list and add position to its items in MongoDB, use sort() combined with forEach() to iterate through the sorted results and assign position values. This approach permanently adds position data to your documents based on the specified sort order. Syntax var i = 1; db.collection.find().sort({fieldName: 1}).forEach(function(doc) { doc.Position = i; i++; db.collection.save(doc); }); Sample Data db.demo581.insertMany([ {"Name": "Chris", "Score": 56}, {"Name": "Bob", "Score": 240}, {"Name": "David", ...
Read MoreSum unique properties in different collection elements in MongoDB and get the resultant Price?
To calculate the sum of unique properties in different collection elements in MongoDB, use $cond along with $group in an aggregation pipeline. This technique allows you to conditionally select which field to use for grouping and then sum the prices for each unique identifier. Syntax db.collection.aggregate([ { $project: { field1: 1, field2: 1, ...
Read MoreMongoDB query to slice only one element of array
To slice only one element of an array in MongoDB, use the $slice operator in the projection stage of a query. This operator allows you to return a specific number of array elements from the beginning or end of an array. Syntax db.collection.find( {}, { "arrayField": { $slice: N } } ); Where N is the number of elements to return (positive for first N elements, negative for last N elements). Sample Data db.demo579.insertOne({ "_id": 101, ...
Read MoreSort MongoDB Collection by Array value?
To sort MongoDB collection by Array value, use aggregate() along with $unwind and $sort. This approach first deconstructs the array elements into separate documents, then sorts by the desired array field. Syntax db.collection.aggregate([ { $unwind: "$arrayField" }, { $sort: { "arrayField.sortField": 1 } } // 1 for ascending, -1 for descending ]); Sample Data db.demo577.insertOne({ "student": { "details": [ { ...
Read MoreSort and get only the first two fields in a "$group" operation in MongoDB
To sort documents and get only the first document per group in MongoDB's $group operation, use $sort before grouping, then $first with $$ROOT to capture the entire document, and finally $project to shape the output fields. Syntax db.collection.aggregate([ { $sort: { "field": 1 } }, { $group: { "_id": "$groupField", "result": { $first: "$$ROOT" } }}, { $project: { ...
Read MoreHide id field in MongoDB
To hide the _id field in MongoDB query results, use the projection parameter in the find() method and set _id: 0. This excludes the _id field from the output while displaying other specified fields. Syntax db.collection.find( { query }, { _id: 0, "field1": 1, "field2": 1 } ); Sample Data db.demo575.insertMany([ {id: 101, Information: {Name: "Chris", Age: 21}}, {id: 102, Information: {Name: "David", Age: 20}}, {id: 101, Information: {Name: "Bob", Age: 23}} ]); ...
Read MoreWorking with Aggregation to match all the values in MongoDB
To match all the values in MongoDB using aggregation, use $match with $and operator to combine multiple conditions. This allows you to filter documents that satisfy all specified criteria simultaneously. Syntax db.collection.aggregate([ { $match: { $and: [ { "field1": "value1" }, ...
Read MoreQuery an array of embedded documents in MongoDB and push another?
To query an array of embedded documents in MongoDB and push another document, use the $push operator along with update(). You can combine array querying with conditional operations to add new documents only when certain conditions are met. Syntax db.collection.update( { _id: documentId, "arrayField.subField": { $nin: ["value"] } }, { $push: { ...
Read MoreFind value above a specific value in MongoDB documents?
To find values above a specific value in MongoDB, use the $gte (greater than or equal to) operator to match documents where a field's value meets or exceeds the specified threshold. Syntax db.collectionName.find({ fieldName: { $gte: value } }); Create Sample Data Let us create a collection with price documents ? db.demo571.insertMany([ { "Price": 140 }, { "Price": 100 }, { "Price": 110 }, { "Price": 240 } ]); ...
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