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MongoDB Questions and answers

Is MongoDB NoSQL database and which kind of NoSQL supported by MongoDB?
Yes MongoDB is based on NoSQL store model. MongoDB is document oriented database in which data objects are store as separate documents inside a collection and does not follow RDBMS.The documents are stored as binary JSON or BSON object.
click here for MongoDB overview

What is namespace in MongoDB?
Concatenation of collection name with database name is called namespace. for example db.book where db is database name and book is the collection name.

What is advantage of MongoDB over SQL database?
MongoDB is document oriented database which is allow highly flexible and scalable feature. MongoDb is schema less means no fixed structure database like SQL. One collection is flexible regarding fields means one row have 10 field, second can have12 fields. MongoDB database is more faster to SQL database due to efficient indexing and storage techniques. Advantage of MongoDB

What is projection in MongoDB
If we want to select necessary field's data then we have to use projection. For more click here

Syntax to create database and collection
syntax to create database
>use database_name
syntax to create collection
>db.createcollection("collection name")
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Does MongoDB is support foreign key
No, MongoDB does not support foreign key.

What is sharding in MongoDB
Sharding is responsible to storing data records across multiple machines. As per demand to manage large amount of data, a single machine is not sufficient to store data nor provide an acceptable medium to read and write data. To resolve this problem MongoDB provide a process called Sharding. Sharding solve the problem with horizontal scaling. Through sahrding, you may add more machines to support data growth and demands of read and write operations. know more

what is a replica set in MongoDB  
A replica set is a group of MongoDB instances that host the same data set. There is two node first is primary node that receives all write operations and secondary, apply operations from the primary so that they have the same data set. Replica set can have only one primary node. know more

Can you move old files in the moveChunk directory?
Yes, it is possible to move old files in the moveChunk directory, during normal shard balancing operations these files are made as backups and can be deleted once the operations are done.

What is indexing in MongoDB
As we know index is technique to arrange data in database which support the efficient resolution of queries. If we run a query to select data, MongoDB do scan every document of collection. Scanning of all document may affect performance of MongoDB when it process the large volume of data.
The index stores the value of a specific field or set of fields, ordered by the value of the field as specified in index. know more
 

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Add day to ISODate in MongoDB

We can use $add operator to add days in ISODate in mongodb, $add is the Arithmetic Aggregation Operator which adds number and date in mongodb.
Syntax:

{ $add: [ <expression1>, <expression2>, ... ] }

Note:  If one of the argument is date $add operator treats to other arguments as milliseconds to add to the date.
Example: Suppose we have a Test collection as below.

{"Title" : "Add day to ISODate in MongoBD","CreatedDate" : ISODate("2016-07-07T08:00:00.000Z")}

Query to add 2 days in CreatedDate

db.Test.aggregate([      { $project: { Title: 1, AddedDate: { $add: [ "$CreatedDate", 2*24*60*60000 ] } } }    ])

Result:

{ "_id" : ObjectId("579a1567ac1b3f3732483de0"), "Title" : "Add day to ISODate in MongoBD", "AddedDate" : ISODate("2016-07-09T08:00:00.000Z") }

Note: As mentioned in above note we have to convert days in millisecond because $add operator treat to other arg…

Remove special character from string in MongoDB

Problem: Suppose wehave a collection and one field is type string contains some special character (like !@#$%) and we don’t want these special character.
Solution: We can easily remove the special character from field using script “replace(/[^a-zA-Z 0-9 ]/g, '')” in our query.  How can we remove special character from string using this script please see following example.
Example: Suppose we have a collection “EduSurvey “where we are collecting information from institutions.

{Name:"JB institute”, About:"This is good one collage for MBA", Information:"This $%%institute ##has good faculty etc$$"}
{Name:"MK institute”, About:"This is good one collage for MCA", Information:"This$$%# is the dummy text12"}
{Name:"MG institute”, About:"This is good one collage for B,Tech", Information:"This# institute@ has&* good infrastructure"}

Did you notice Information fields contains some special character so we…