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Database Articles
Page 236 of 546
How to specify the order in which the query returns matching documents in MongoDB
To specify the order in which the query returns matching documents, use cursor.sort() in MongoDB. The cursor is db.collectionName.find().Let us create a collection with documents −> db.demo259.insertOne({"Subject":"MySQL"}); { "acknowledged" : true, "insertedId" : ObjectId("5e47ae1f1627c0c63e7dba98") } > db.demo259.insertOne({"Subject":"Java"}); { "acknowledged" : true, "insertedId" : ObjectId("5e47ae231627c0c63e7dba99") } > db.demo259.insertOne({"Subject":"MongoDB"}); { "acknowledged" : true, "insertedId" : ObjectId("5e47ae281627c0c63e7dba9a") }Display all documents from a collection with the help of find() method −> db.demo259.find();This will produce the following output −{ "_id" : ObjectId("5e47ae1f1627c0c63e7dba98"), "Subject" : "MySQL" } { "_id" : ObjectId("5e47ae231627c0c63e7dba99"), "Subject" : "Java" } { "_id" : ObjectId("5e47ae281627c0c63e7dba9a"), "Subject" ...
Read MoreHow to pull value from array of ObjectIDs in MongoDB?
To pull value from array of ObjectIDs, use $pull in MongoDB. Let us create a collection with documents −> db.demo258.insertOne({"arrayOfObjectsId":[ ObjectId("5e47a5e81627c0c63e7dba92"), ObjectId("5e47a5e51627c0c63e7dba91")]}); { "acknowledged" : true, "insertedId" : ObjectId("5e47a8211627c0c63e7dba97") }Display all documents from a collection with the help of find() method −> db.demo258.find();This will produce the following output −{ "_id" : ObjectId("5e47a8211627c0c63e7dba97"), "arrayOfObjectsId" : [ ObjectId("5e47a5e81627c0c63e7dba92"), ObjectId("5e47a5e51627c0c63e7dba91") ] }Following is the query to pull value from array of ObjectIDs −> db.demo258.update( { }, { $pull: { arrayOfObjectsId: { $in: [ ObjectId("5e47a5e81627c0c63e7dba92") ] } } } ); WriteResult({ "nMatched" : 1, "nUpserted" : 0, "nModified" : 1 })Display all ...
Read MoreSet MongoDB compound index with a fixed value field
For this, we will use the concept of createIndex() and create index −> db.compoundIndexDemo.createIndex({"StudentName":1, "StudentAge":1}, {unique:true}); { "createdCollectionAutomatically" : true, "numIndexesBefore" : 1, "numIndexesAfter" : 2, "ok" : 1 }Let us first create a collection with documents −> db.compoundIndexDemo.insertOne({"StudentName":"Chris"}); { "acknowledged" : true, "insertedId" : ObjectId("5e084c1d25ddae1f53b62207") } > db.compoundIndexDemo.insertOne({"StudentName":"Chris", "StudentAge":23}); { "acknowledged" : true, "insertedId" : ObjectId("5e084c5625ddae1f53b62209") } > db.compoundIndexDemo.insertOne({"StudentName":"Chris", "StudentAge":22}); { "acknowledged" : true, "insertedId" : ObjectId("5e084c5b25ddae1f53b6220a") } > db.compoundIndexDemo.insertOne({"StudentName":"Chris", "StudentAge":23}); 2019-12-29T12:19:02.225+0530 E QUERY [js] WriteError: E11000 duplicate key error collection: web.compoundIndexDemo index: StudentName_1_StudentAge_1 dup key: { : "Chris", ...
Read MoreUpdate 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 ...
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