Creating, Updating and Deleting Document in MongoDB

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MongoDBCreating, Updating and Deleting Document

Wildan [email protected]

http://www.negeripelangi.com/

http://www.openthinklabs.com/


Overview● Adding new documents to a collection

● Inserting and Saving Documents

– Batch Insert

– Inserts: Internals and Implications

● Removing documents from a collection● Removing Documents

– Remove Speed

● Updating existing documents● Document Replacement

● Using Modifiers

● Upserts

● Choosing the correct level of safety versus speed for all of these operations● The Fastest Write This Side of Mississippi


Inserting and Saving Documents● Inserts are the basic method for adding data to

MongoDB. To insert a document into a collection, use the collection’s insert method:

> db.foo.insert({"bar" : "baz"})


Batch Insert● If you have a situation where you are inserting multiple documents into a

collection, you can make the insert faster by using batch inserts. Batch inserts allow you to pass an array of documents to the database.

● A batch insert is a single TCP request, meaning that you do not incur the overhead of doing hundreds of individual requests

● Batch inserts are intended to be used in applications, such as for inserting a couple hundred sensor data points into an analytics collection at once.

● They are useful only if you are inserting multiple documents into a single collection

● Current versions of MongoDB do not accept messages longer than 16MB


Inserts: Internals and Implications● When you perform an insert, the driver you are

using converts the data structure into BSON, which it then sends to the database

● The database understands BSON and checks for an "_id" key and that the document’s size does not exceed 4MB, but other than that, it doesn’t do data validation; it just saves the document to the database as is.


Removing Documents● Now that there’s data in our database, let’s delete

it.● > db.users.remove()

● This will remove all of the documents in the users collection. This doesn’t actually remove the collection, and any indexes created on it will still exist.

● The remove function optionally takes a query document as a parameter.

● > db.mailing.list.remove({"opt-out" : true})


Remove Speed● Removing documents is usually a fairly quick operation, but if

you want to clear an entire collection, it is faster to drop it (and then re-create any indexes).

for i in range(1000000):collection.insert({"foo": "bar", "baz": i, "z": 10 - i})

import timefrom pymongo import Connectiondb = Connection().foocollection = db.barstart = time.time()collection.remove()collection.find_one()total = time.time() - startprint "%d seconds" % total

46.08 s

import timefrom pymongo import Connectiondb = Connection().foocollection = db.barstart = time.time()db.drop_collection("bar") total = time.time() - startprint "%d seconds" % total

0.01 s


Updating Documents● Once a document is stored in the database, it can be changed using the update method

● update takes two parameters: a query document, which locates documents to update, and a modifier document, which describes the changes to make to the documents found.

● Updates are atomic: if two updates happen at the same time, whichever one reaches the server first will be applied, and then the next one will be applied. Thus, conflicting

● updates can safely be sent in rapid-fire succession without any documents being corrupted: the last update will “win.”


Document Replacement

{"_id" : ObjectId("4b2b9f67a1f631733d917a7a"),"name" : "joe","friends" : 32,"enemies" : 2}

{"_id" : ObjectId("4b2b9f67a1f631733d917a7a"),"username" : "joe","relationships" :{"friends" : 32,"enemies" : 2}}

We want to change that document into the following:


Document Replacement

> var joe = db.users.findOne({"name" : "joe"});> joe.relationships = {"friends" : joe.friends, "enemies" : joe.enemies};{"friends" : 32,"enemies" : 2}

> joe.username = joe.name;"joe"> delete joe.friends;true> delete joe.enemies;true> delete joe.name;true> db.users.update({"name" : "joe"}, joe);


Common Mistake

> db.people.find(){"_id" : ObjectId("4b2b9f67a1f631733d917a7b"), "name" : "joe", "age" : 65},{"_id" : ObjectId("4b2b9f67a1f631733d917a7c"), "name" : "joe", "age" : 20},{"_id" : ObjectId("4b2b9f67a1f631733d917a7d"), "name" : "joe", "age" : 49},

> joe = db.people.findOne({"name" : "joe", "age" : 20});{"_id" : ObjectId("4b2b9f67a1f631733d917a7c"),"name" : "joe","age" : 20}> joe.age++;> db.people.update({"name" : "joe"}, joe);E11001 duplicate key on update


Using Modifiers● Usually only certain portions of a document need

to be updated.● Partial updates can be done extremely efficiently

by using atomic update modifiers● Update modifiers are special keys that can be

used to specify complex update operations, such as altering, adding, or removing keys, and even manipulating arrays and embedded documents.


Using Modifiers{"_id" : ObjectId("4b253b067525f35f94b60a31"),"url" : "www.example.com","pageviews" : 52}

> db.analytics.update({"url" : "www.example.com"},... {"$inc" : {"pageviews" : 1}})

use the "$inc"modifier to increment the value of the "pageviews" key.

> db.analytics.find(){"_id" : ObjectId("4b253b067525f35f94b60a31"),"url" : "www.example.com","pageviews" : 53}


Getting started with the "$set" modifier

● "$set" sets the value of a key. If the key does not yet exist, it will be created. This can be handy for updating schema or adding user-defined keys


> db.users.findOne(){"_id" : ObjectId("4b253b067525f35f94b60a31"),"name" : "joe","age" : 30,"sex" : "male","location" : "Wisconsin"}

> db.users.update({"_id" : ObjectId("4b253b067525f35f94b60a31")},... {"$set" : {"favorite book" : "war and peace"}})

> db.users.findOne(){"_id" : ObjectId("4b253b067525f35f94b60a31"),"name" : "joe","age" : 30,"sex" : "male","location" : "Wisconsin","favorite book" : "war and peace"}

> db.users.update({"name" : "joe"},... {"$set" : {"favorite book" : "green eggs and ham"}})



● "$set" can even change the type of the key it modifies. For instance, if our fickle user decides that he actually likes quite a few books, he can change the value of the “favorite book” key into an array:

> db.users.update({"name" : "joe"},... {"$set" : {"favorite book" :... ["cat's cradle", "foundation trilogy", "ender's game"]}})

> db.users.update({"name" : "joe"},... {"$unset" : {"favorite book" : 1}})

remove the key altogetherwith "$unset"



● You can also use "$set" to reach in and change embedded documents:

> db.blog.posts.findOne(){"_id" : ObjectId("4b253b067525f35f94b60a31"),"title" : "A Blog Post","content" : "...","author" : {"name" : "joe","email" : "[email protected]"}}

> db.blog.posts.update({"author.name" : "joe"}, {"$set" : {"author.name" : "joe schmoe"}})

> db.blog.posts.findOne(){"_id" : ObjectId("4b253b067525f35f94b60a31"),"title" : "A Blog Post","content" : "...","author" : {"name" : "joe schmoe","email" : "[email protected]"}}


Incrementing and decrementing● The "$inc" modifier can be used to change the value for an existing

key or to create a new key if it does not already exist. It is very useful for updating analytics, karma, votes, or anything else that has a changeable, numeric value.

> db.games.insert({"game" : "pinball", "user" : "joe"})

> db.games.update({"game" : "pinball", "user" : "joe"},... {"$inc" : {"score" : 50}})

> db.games.findOne(){"_id" : ObjectId("4b2d75476cc613d5ee930164"),"game" : "pinball","name" : "joe","score" : 50}


Incrementing and decrementing

> db.games.update({"game" : "pinball", "user" : "joe"},... {"$inc" : {"score" : 10000}})

> db.games.find(){"_id" : ObjectId("4b2d75476cc613d5ee930164"),"game" : "pinball","name" : "joe","score" : 10050}

"$inc" is similar to "$set", but it is designed for incrementing (and decrementing)numbers. "$inc" can be used only on values of type integer, long, or double. If it is usedon any other type of value, it will fail.


To be continued … ^_^


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Q&A

Thanks! ^_^

Creating, Updating and Deleting Document in MongoDB

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