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Database Articles
Page 238 of 546
Update MongoDB variable value with variable itself?
You cannot update a column value using itself. For this, you can use $set. Let us create a collection with documents −> db.demo256.insertOne({"Name":"Chris"}); { "acknowledged" : true, "insertedId" : ObjectId("5e47a3e91627c0c63e7dba8b") } > db.demo256.insertOne({"Name":"Bob"}); { "acknowledged" : true, "insertedId" : ObjectId("5e47a3ea1627c0c63e7dba8c") } > db.demo256.insertOne({"Name":"David"}); { "acknowledged" : true, "insertedId" : ObjectId("5e47a3eb1627c0c63e7dba8d") }Display all documents from a collection with the help of find() method −> db.demo256.find();This will produce the following output −{ "_id" : ObjectId("5e47a3e91627c0c63e7dba8b"), "Name" : "Chris" } { "_id" : ObjectId("5e47a3ea1627c0c63e7dba8c"), "Name" : "Bob" } { "_id" : ObjectId("5e47a3eb1627c0c63e7dba8d"), "Name" : "David" }Following is ...
Read MoreSplit a string during MongoDB aggregate
For this, use mapReduce(). Let us first create a collection with documents −> db.splitString.insertOne({"StudentName":"John Smith"}); { "acknowledged" : true, "insertedId" : ObjectId("5e0849d925ddae1f53b62206") }Following is the query to display all documents from a collection with the help of find() method −> db.splitString.find().pretty();This will produce the following output −{ "_id" : ObjectId("5e0849d925ddae1f53b62206"), "StudentName" : "John Smith" }Here is the query to split a string −> db.splitString.mapReduce( ... function() { ... var StudentLastName = this.StudentName.split(/\s/).reverse()[0].toUpperCase(); ... ... emit({ "StudentLastName": StudentLastName, "FirstObjectId": this._id }, this); ... }, ... function(){}, ... ...
Read MoreMongoDB bulk insert for documents
For bulk insert, you can use insert() in MongoDB. Let us create a collection with documents −> var manyDocument = db.demo255.initializeUnorderedBulkOp(); > manyDocument.insert( { "Name":"Chris", Age:24} ); > manyDocument.insert( {"Name":"Bob", Age:22 } ); > manyDocument.insert( { "Name":"David", Age:23 } ); > manyDocument.execute(); BulkWriteResult({ "writeErrors" : [ ], "writeConcernErrors" : [ ], "nInserted" : 3, "nUpserted" : 0, "nMatched" : 0, "nModified" : 0, "nRemoved" : 0, "upserted" : [ ] })Display all documents from a collection with the help of find() method −> db.demo255.find();This will produce the following output −{ "_id" : ...
Read MoreMongoDB query to 'sort' and display a specific number of values
To sort in MongoDB, use sort(). For displaying only a specific number of values, use LIMIT. Let us create a collection with documents −> db.demo254.insertOne({"Name":"Chris"}); { "acknowledged" : true, "insertedId" : ObjectId("5e47a0ab1627c0c63e7dba7f") } > db.demo254.insertOne({"Name":"Adam"}); { "acknowledged" : true, "insertedId" : ObjectId("5e47a0b01627c0c63e7dba80") } > db.demo254.insertOne({"Name":"Bob"}); { "acknowledged" : true, "insertedId" : ObjectId("5e47a0b71627c0c63e7dba81") }Display all documents from a collection with the help of find() method −> db.demo254.find();This will produce the following output −{ "_id" : ObjectId("5e47a0ab1627c0c63e7dba7f"), "Name" : "Chris" } { "_id" : ObjectId("5e47a0b01627c0c63e7dba80"), "Name" : "Adam" } { "_id" : ObjectId("5e47a0b71627c0c63e7dba81"), "Name" : "Bob" ...
Read MoreMongoDB query to change simple field into an object?
Fir this, you can use $rename. Let us first create a collection with documents −> db.changeSimpleFieldDemo.insertOne({"StudentMarks":58, "StudentSubject":"MySQL"}); { "acknowledged" : true, "insertedId" : ObjectId("5e0847a825ddae1f53b62205") }Following is the query to display all documents from a collection with the help of find() method −> db.changeSimpleFieldDemo.find();This will produce the following output −{ "_id" : ObjectId("5e0847a825ddae1f53b62205"), "StudentMarks" : 58, "StudentSubject" : "MySQL" }Here is the query to change a field into an object. The “obj” field is a temporary field name we have used below −> db.changeSimpleFieldDemo.update({}, {$rename: {Student: 'obj'}}, {multi: true}); WriteResult({ "nMatched" : 1, "nUpserted" : 0, "nModified" : 0 ...
Read MoreMongoDB query to fetch array values
Use find() along with $elemMatch to fetch array values. Let us first create a collection with documents −> db.fetchingArrayValuesDemo.insertOne( ... { ... "StudentName": "David", ... "StudentDetails": [ ... { ... "FatherName": "Bob", ... "CountryName": "US", ... ... "Favourite": [ ... { ... "Teacher": "DAVID", ... "Subject": [ ... "MySQL", ... ...
Read MoreMongoDB indexes not working when executing $elemMatch?
To implement indexes correctly with $elemMatch, you need to use the concept of explain(). Let us first create a collection with documents −> db.workingOfIndexesDemo.createIndex({"Information.StudentDetails.StudentName":1}, { sparse : true, background : true } ); { "createdCollectionAutomatically" : true, "numIndexesBefore" : 1, "numIndexesAfter" : 2, "ok" : 1 } > db.workingOfIndexesDemo.insertOne({"Information":{"StudentDetails":{"StudentName":"Chris"}}}); { "acknowledged" : true, "insertedId" : ObjectId("5e06f94825ddae1f53b621f7") } > db.workingOfIndexesDemo.insertOne({"Information":{"StudentDetails":{"StudentName":"David"}}}); { "acknowledged" : true, "insertedId" : ObjectId("5e06f94f25ddae1f53b621f8") } > db.workingOfIndexesDemo.insertOne({"Information":{"StudentDetails":{"StudentName":"Mike"}}}); { "acknowledged" : true, "insertedId" : ObjectId("5e06f95325ddae1f53b621f9") }Following is the query to display all documents from a collection with the help ...
Read MoreImplement a MongoDB $cond field in a projection pipeline based on the presence or absence of a field?
For this, you can use $cond along with $anyElementTrue. NULL values (absence of a field) would evaluate to FALSE. With that, an empty array also returns FALSE with $ anyElementTrue.Let us first create a collection with documents −> db.presenceDemo.insertOne({"StudentName":null}); { "acknowledged" : true, "insertedId" : ObjectId("5e06f70c25ddae1f53b621f3") } > db.presenceDemo.insertOne({"StudentName":"Chris"}); { "acknowledged" : true, "insertedId" : ObjectId("5e06f71425ddae1f53b621f4") } > db.presenceDemo.insertOne({"StudentName":null}); { "acknowledged" : true, "insertedId" : ObjectId("5e06f71825ddae1f53b621f5") } > db.presenceDemo.insertOne({"StudentName":"David"}); { "acknowledged" : true, "insertedId" : ObjectId("5e06f71e25ddae1f53b621f6") }Following is the query to display all documents from a collection with the help of find() ...
Read MoreHow can I search a collection to find a nested value in one of its documents in MongoDB?
For this, use double underscore( __) in find(). Let us first create a collection with documents −> db.nestedDemo.insertOne({"Information":{"__StudentName":"John Smith"}}); { "acknowledged" : true, "insertedId" : ObjectId("5e06f39125ddae1f53b621f0") } > db.nestedDemo.insertOne({"Information":{"__StudentName":"John Doe"}}); { "acknowledged" : true, "insertedId" : ObjectId("5e06f39e25ddae1f53b621f1") } > db.nestedDemo.insertOne({"Information":{"__StudentName":"Chris Brown"}}); { "acknowledged" : true, "insertedId" : ObjectId("5e06f3a625ddae1f53b621f2") }Following is the query to display all documents from a collection with the help of find() method −> db.nestedDemo.find().pretty();This will produce the following output −{ "_id" : ObjectId("5e06f39125ddae1f53b621f0"), "Information" : { "__StudentName" : "John Smith" } } { "_id" ...
Read MoreFind MongoDB document with array containing the maximum occurrence of a specific value
For this, you can use aggregate(). Let us first create a collection with documents −> db.countOccurrencesDemo.insertOne({"ListOfValues":[65, 87, 89, 65, 67, 87, 87, 87]}); { "acknowledged" : true, "insertedId" : ObjectId("5e06ef9325ddae1f53b621eb") } > db.countOccurrencesDemo.insertOne({"ListOfValues":[102, 65, 87, 65, 89, 65, 89, 65, 89, 65]}); { "acknowledged" : true, "insertedId" : ObjectId("5e06efaa25ddae1f53b621ec") }Following is the query to display all documents from a collection with the help of find() method −> db.countOccurrencesDemo.find();This will produce the following output −{ "_id" : ObjectId("5e06ef9325ddae1f53b621eb"), "ListOfValues" : [ 65, 87, 89, 65, 67, 87, 87, 87 ] } { "_id" : ObjectId("5e06efaa25ddae1f53b621ec"), "ListOfValues" : ...
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