You can use projection operator $elemMatch to filter in queried element in an object array in MongoDB collection. To retrieve only the queried element in an object array in MongoDB, let us first create a collection with documents object array.The query is as follows:> db.objectArray.insert({"Persons":[    {"PersonName":"Adam", "PersonSalary":25000}, {"PersonName":"Larry", "PersonSalary":27000    }]});    WriteResult({ "nInserted" : 1 }) > db.objectArray.insert({"Persons":[    {"PersonName":"David", "PersonSalary":32000}, {"PersonName":"Carol", "PersonSalary":77000    }]});    WriteResult({ "nInserted" : 1 })Now you can display all the documents with the help of find(). The query is as follows:> db.objectArray.find().pretty();The following is the output:{    "_id" : ObjectId("5c6bfadc68174aae23f5ef53"),    "Persons" ... Read More

To retrieve documents from a collection in MongoDB, you need to use find() method. The syntax is as follows:db.yourCollectionName.find();The above syntax will return all the documents from a collection in MongoDB. To understand the above syntax, let us create a collection with documents. The query to create documents are as follows:> db.retrieveAllStudents.insertOne({"StudentId":"STUD101", "StudentName":"David", "StudentAge":24}); {    "acknowledged" : true, "insertedId" : ObjectId("5c6bf5cf68174aae23f5ef4e") } > db.retrieveAllStudents.insertOne({"StudentId":"STUD102", "StudentName":"Carol", "StudentAge":22}); {    "acknowledged" : true, "insertedId" : ObjectId("5c6bf5e968174aae23f5ef4f") } > db.retrieveAllStudents.insertOne({"StudentId":"STUD103", "StudentName":"Maxwell", "StudentAge":25}); {    "acknowledged" : true, "insertedId" : ObjectId("5c6bf5f768174aae23f5ef50") } > db.retrieveAllStudents.insertOne({"StudentId":"STUD104", "StudentName":"Bob", "StudentAge":23}); {    "acknowledged" : true, "insertedId" : ... Read More

If you want to delete all documents from the collection, you can use deleteMany(). Let us first create a collection and insert some documents to it:> db.deleteDocumentsDemo.insert({"Name":"Larry", "Age":23}); WriteResult({ "nInserted" : 1 }) > db.deleteDocumentsDemo.insert({"Name":"Mike", "Age":21}); WriteResult({ "nInserted" : 1 }) > db.deleteDocumentsDemo.insert({"Name":"Sam", "Age":24}); WriteResult({ "nInserted" : 1 })Now display all the documents from the collection. The query is as follows:> db.deleteDocumentsDemo.find().pretty();The following is the output:{    "_id" : ObjectId("5c6ab0e064f3d70fcc914805"),    "Name" : "Larry",    "Age" : 23 } {    "_id" : ObjectId("5c6ab0ef64f3d70fcc914806"),    "Name" : "Mike",    "Age" : 21 } {    "_id" : ObjectId("5c6ab0f864f3d70fcc914807"),    "Name" ... Read More

To delete document from a collection in MongoDB, you can use the deleteOne() method. Let us first create a collection and insert some documents to it:> db.deleteDocumentsDemo.insert({"Name":"Larry", "Age":23}); WriteResult({ "nInserted" : 1 }) > db.deleteDocumentsDemo.insert({"Name":"Mike", "Age":21}); WriteResult({ "nInserted" : 1 }) > db.deleteDocumentsDemo.insert({"Name":"Sam", "Age":24}); WriteResult({ "nInserted" : 1 })Now display all the documents from the collection. The query is as follows:> db.deleteDocumentsDemo.find().pretty();The following is the output:{    "_id" : ObjectId("5c6ab0e064f3d70fcc914805"),    "Name" : "Larry",    "Age" : 23 } {    "_id" : ObjectId("5c6ab0ef64f3d70fcc914806"),    "Name" : "Mike",    "Age" : 21 } { "_id" : ObjectId("5c6ab0f864f3d70fcc914807"), "Name" : "Sam", ... Read More

To delete the documents from a collection in MongoDB, you need to use remove() method. The syntax is as follows:db.yourCollectionName.remove(yourDeleteValue);Here, let us create a collection with some documents. The query is as follows:>db.deleteDocuments.insert({"UserId":1, "UserName":"Bob", "UserTechnicalSubject":"Introducti on to PL/SQL"}); WriteResult({ "nInserted" : 1 }) >db.deleteDocuments.insert({"UserId":2, "UserName":"Carol", "UserTechnicalSubject":"Introduction to MongoDB"}); WriteResult({ "nInserted" : 1 }) >db.deleteDocuments.insert({"UserId":3, "UserName":"John", "UserTechnicalSubject":"Introduction to MySQL"}); WriteResult({ "nInserted" : 1 }) >db.deleteDocuments.insert({"UserId":4, "UserName":"Maxwell", "UserTechnicalSubject":"Introduction to SQL Server"}); WriteResult({ "nInserted" : 1 })You can display all documents from the collection we created above with the help of find() command. The query is as follows:> db.deleteDocuments.find().pretty();The following ... Read More

To insert new documents into a MongoDB collection, you need to use insert() method or save() method.Case 1: Using insert() method.The syntax is as follows:db.yourCollectionName.insert(yourDocument);Case 2: Using save() method.The syntax is as follows:db.yourCollectionName.save(yourDocument);In the above syntax, if your collection name does not exist then MongoDB will create a new collection and insert the document in the collection.The query to insert new documents is as follows for both the cases discussed above.Case 1: Using insert() method. The query is as follows:> db.userInformation.insert({    ... "Name":"John",    ... Age:30,    ... isStudent:false,    ... "Subjects":["Introduction to java", "Introduction to MongoDB"]    ... ... Read More

Open source databases are those databases who have an open source code i.e anyone may view the code, study it or even modify it. Open source databases could be relational (SQL) or non relational (NoSQL).Why use Open Source Databases?It is quite expensive to create and maintain a database for any company. A huge chunk of the total software expenditure is used to handle databases. So, it is feasible to switch to low cost open source databases. This saves companies a lot of money in the long run.Open Source Databases in useThere many different open source databases in the market. All ... Read More

By using pymongo library, we can insert a Python object into MongoDB, which is a widely used MongoDB driver for Python. To insert a Python object represented as a dictionary, we have to establish the setup for a MongoDB client and connect to a database and collection. Before starting, ensure you have installed Python 3 (along with PIP) and MongoDB. The following are the steps for inserting a Python object in MongoDB. Install PyMongo ... Read More