Introduction to Mongo DB updating Document Part2

Rama Sagar
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MongoDB can be used as a file system, taking advantage of load balancing and data replication features over multiple machines for storing files.
Recommendation
Read Introduction to Mongo DB updating Document before this article.

Introduction

In this article we will learn how to update document in mongo dB with a practical example.

Previous articles covered an introduction to mongo dB and the set up and installation, and few command line options.You can access those articles from here:

Objective

The objective of the article is to learn about updating document in Mongo database.

Updating Document

In previous article we have seen how to update a document using update command here we will see some more options of updating a document.

Now lets consider some array operations

We can see below that I have a document with only an id field

db.a.save ({_id:1});

Now if we want here an array containing some values in this document

We can issue the update with the push command to add an item to an array

db.a.update ({_id:1}, {$push :{ things: ’one’}});

Lets put some more items

db.a.update ({_id:1}, {$push :{ things: ‘two’}});

db.a.update ({_id:1}, {$push :{ things: ‘three’}});

db.a.update ({_id:1}, {$push :{ things: ‘three’}});

 

We can find that it has the element three twice that might be something we don’t want.. We can restrict it by using addToSet operator

db.a.update ({_id:1}, {$addToSet :{ things: ‘four’}});

We can notice that the element four didn't added again



We can still see three is hanging in which  we doesnt need we can remove it out of the array by using pull operator and can add it again as shown..

db.a.update ({_id:1}, {$pull :{ things: ‘three}});

It will delete all the instances of three in the array as shown below



Now if we want to remove the last element and first element in an array we can use pop operator as shown below

For last element

db.a.update ({_id:1}, {$pop :{ things: 1}});

For First element we can use negative value

db.a.update ({_id:1}, {$pop :{ things: -1}});



Now lets consider a scenario where we had multiple records in the database...if we wanna apply an update to several of them




Lets see if we wanna push another element in them using the update command with an empty query we can do it

db.a.update ({}, {$push :{ things: 4}});



But we can see that only one record was effected this is because the default options of an update is fixed to one record.

we can fix it by using the multiple options true

db.a.update ({}, {$push :{ things: 4}},{multi:true));



Conclusion

In this article we have seen different options in updating a document in mongo database.In coming articles we will see more about querying.

Reference

http://bsonspec.org/
http://www.mongodb.org/ 

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About the Author

Rama Sagar
Full Name: RamaSagar Pulidindi
Member Level: Silver
Member Status: Member,MVP
Member Since: 12/30/2012 1:51:40 AM
Country: India
ramasagar
http://www.ramasagar.com
A Software Profesional working in Microsoft .NET technologies since year 2008, and I work for Dake ACE. I am passionate about .NET technology and love to contribute to the .NET community at Dot Net Funda

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