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Database Articles
Page 37 of 547
MongoDB $addToSet to add a deep nested array of object?
The $addToSet operator adds a value to an array unless the value is already present, in which case $addToSet does nothing to that array. When working with deep nested arrays, combine $addToSet with the positional operator $ to target specific array elements. Syntax db.collection.update( { "parentArray.field": "matchValue" }, { $addToSet: { "parentArray.$.nestedArray": newObject } } ); Sample Data Let us first create a collection with documents − db.demo380.insertOne({ "details": [ { ...
Read MoreMongoDB projection on specific nested properties?
To project specific nested properties in MongoDB, use the aggregation pipeline with $addFields, $objectToArray, $filter, and $arrayToObject operators to selectively include nested fields based on conditions. Syntax db.collection.aggregate([ { "$addFields": { "nested.path": { "$arrayToObject": { "$filter": { ...
Read MoreManipulating subdocuments in MongoDB
To manipulate subdocuments in MongoDB, use dot notation to target specific fields within embedded documents or arrays. The $ positional operator helps update elements that match query conditions. Syntax db.collection.update( { "arrayField.field": "matchValue" }, { $operation: { "arrayField.$.targetField": value } } ); Create Sample Data db.demo378.insertOne({ Name: "Chris", details: [ { id: 101, Score: 56 }, { id: 102, Score: 78 ...
Read MoreHow can I concatenate an array of integer in MongoDB aggregation method?
To concatenate an array of integers in MongoDB aggregation, use the $reduce operator with $concat to combine array elements into a single string. Since integers must be converted to strings for concatenation, use $toString for type conversion. Syntax db.collection.aggregate([ { $project: { concatenatedField: { $reduce: { ...
Read MoreHow to update after aggregate in MongoDB?
To update documents after performing aggregation analysis in MongoDB, you cannot directly update within the aggregation pipeline. Instead, use the update() method with array filters to target specific array elements based on conditions. Syntax db.collection.update( { "field": value }, { $inc: { "arrayField.$[identifier].field": incrementValue } }, { arrayFilters: [{ "identifier.field": condition }] } ); Sample Data Let us first create a collection with documents ? db.demo376.insertOne({ "id": 101, "details": [ ...
Read MoreMongoDB query to execute stored function?
JavaScript functions can be saved for reuse using a system collection called system.js. To store a function, use db.collection.save(), then execute it with db.eval(). Syntax // Store function db.system.js.save({ _id: "functionName", value: function(parameters) { // function body return result; } }); // Execute function db.eval("functionName(arguments)"); Example: Store and Execute Function Let us first create a function ? db.system.js.save({ _id: ...
Read MoreMongoDB difference between show dbs and show databases?
In MongoDB, there is no functional difference between show dbs and show databases. Both commands are aliases that internally call the same listDatabases command and produce identical output. Syntax show dbs OR show databases Example: Using show dbs show dbs admin 0.002GB app 0.000GB business 0.000GB config 0.000GB ...
Read MoreFind when the keys are unknown in MongoDB?
To find documents when the keys are unknown in MongoDB, use $addFields with $objectToArray to convert documents into key-value arrays, then search through the values dynamically. Syntax db.collection.aggregate([ { "$addFields": { "arrayField": { "$objectToArray": "$$ROOT" } }}, { "$match": { "arrayField.v.fieldName": "searchValue" }}, { "$project": { "arrayField": 0 }} ]) Sample Data db.demo375.insertMany([ { "details": { ...
Read MoreFind values group by another field in MongoDB?
To group by another field in MongoDB, use $group along with $project. This approach allows you to aggregate documents based on a specific field while collecting values from other fields. Syntax db.collection.aggregate([ {$match: {field: "value"}}, {$group: {"_id": "$groupByField", "collectedField": {$addToSet: "$fieldToCollect"}}}, {$project: {"_id": 0, "groupByField": "$_id", "collectedField": 1}} ]); Sample Data db.demo374.insertMany([ { "Name": "Chris", "HobbyDetails": ["Reading Book", "Playing Football"], ...
Read MoreHow to index and sort with pagination using custom field in MongoDB?
To implement index and sorting with pagination using custom fields in MongoDB, combine compound indexes with sort(), limit(), and skip() methods. This approach ensures efficient query performance for paginated results. Syntax db.collection.createIndex({"field1": 1, "field2": 1}); db.collection.find().sort({"field1": 1, "field2": 1}).limit(pageSize).skip(pageNumber * pageSize); Create Sample Data First, create a compound index on Name and CountryName fields for optimal sorting performance ? db.demo373.createIndex({"Name": 1, "CountryName": 1}); { "createdCollectionAutomatically": true, "numIndexesBefore": 1, "numIndexesAfter": 2, "ok": 1 } ...
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