Creating, Updating and Deleting Document in MongoDB

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MongoDB
Creating, Updating and Deleting Document
Wildan Maulana
wildan.m@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 time
from pymongo import Connection
db = Connection().foo
collection = db.bar
start = time.time()
collection.remove()
collection.find_one()
total = time.time() - start
print "%d seconds" % total
46.08 s
import time
from pymongo import Connection
db = Connection().foo
collection = db.bar
start = time.time()
db.drop_collection("bar")
total = time.time() - start
print "%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()
{
"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()
{
"name" : "joe",
"age" : 30,
"sex" : "male",
"location" : "Wisconsin"
}
> db.users.update({"_id" : ObjectId("4b253b067525f35f94b60a31")},
... {"$set" : {"favorite book" : "war and peace"}})
> db.users.findOne()
{
"name" : "joe",
"age" : 30,
"sex" : "male",
"location" : "Wisconsin",
"favorite book" : "war and peace"
}
> db.users.update({"name" : "joe"},
... {"$set" : {"favorite book" : "green eggs and ham"}})

the "$set" modifier
● "$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:
... {"$set" : {"favorite book" :
... ["cat's cradle", "foundation trilogy", "ender's game"]}})
... {"$unset" : {"favorite book" : 1}})
remove the key altogether
with "$unset"

the "$set" modifier
● You can also use "$set" to reach in and change
embedded documents:
> db.blog.posts.findOne()
{
"title" : "A Blog Post",
"content" : "...",
"author" : {
"name" : "joe",
"email" : "joe@example.com"
}
}
> db.blog.posts.update({"author.name" : "joe"}, {"$set" : {"author.name" : "joe schmoe"}})
> db.blog.posts.findOne()
{
"title" : "A Blog Post",
"content" : "...",
"author" : {
"name" : "joe schmoe",
"email" : "joe@example.com"
}
}

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 used
on any other type of value, it will fail.

To be continued … ^_^

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Q&A
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Creating, Updating and Deleting Document in MongoDB

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