Reference Cards

for MongoDB

What is MongoDB?
MongoDB is an open-source, general
purpose database.
Instead of storing data in rows and columns as one would with
a relational database, MongoDB uses a document data model,
and stores a binary form of JSON documents called BSON.
Documents contain one or more fields, and each field contains
a value of a specific data type, including arrays and binary data.
Documents are stored in collections, and collections are stored
in databases. It may be helpful to think of documents as roughly
equivalent to rows in a relational database; fields as equivalent
to columns; and collections as tables. There are no fixed
schemas in MongoDB, so documents can vary in structure and
can be adapted dynamically.
MongoDB provides full index support, including secondary,
compound, and geospatial indexes. MongoDB also features a
rich query language, atomic update modifiers, text search, the
Aggregation Framework for analytics similar to SQL GROUP
BY operations, and MapReduce for complex in-place data
analysis.
Built-in replication with automated failover provides high
availability. Auto-sharding enables horizontal scaling for large
deployments. MongoDB also provides native, idiomatic drivers
for all popular programming languages and frameworks to
make development natural.

Queries

Queries
Queries and What They Match

{a: 10}

Docs where a is 10, or an array containing

the value 10.

{a: 10, b: hello}

Docs where a is 10 and b is hello.

{a: {$gt: 10}}

Docs where a is greater than 10. Also

available: $lt (<), $gte (>=), $lte
(<=), and $ne (!=).

{a: {$in: [10, hello]}}

Docs where a is either 10 or hello.

{a: {$all: [10, hello]}}

Docs where a is an array containing both

10 and hello.

{"a.b": 10}

Docs where a is an embedded document

with b equal to 10.

{a: {$elemMatch: {b: 1, c: 2}}}

Docs where a is an array that contains an

element with both b equal to 1 and c equal
to 2.

{$or: [{a: 1}, {b: 2}]}

Docs where a is 1 or b is 2.

{a: /^m/}

Docs where a begins with the letter m.

One can also use the regex operator: {a:
{$regex: ^m}}.

{a: {$mod: [10, 1]}}

Docs where a mod 10 is 1.

{a: {$type: 2}}

Docs where a is a string. See bsonspec.org

for more.

{ $text: { $search: hello } }

Docs that contain hello on a text

search. Requires a text index.

Queries and What They Match (continued)

{a: {$near:
{$geometry:{
type: Point,
coordinates: [ -73.98,
40.75 ]
}}
} }

Docs sorted in order of nearest to farthest

from the given coordinates. For geospatial
queries one can also use $geoWithin
and $geoIntersects operators.

Not Indexable Queries

The following queries cannot use indexes. These query forms should normally be
accompanied by at least one other query term which does use an index.

{a: {$nin: [10, hello]}}

Docs where a is anything but 10 or

hello.

{a: {$size: 3}}

Docs where a is an array with exactly 3

elements.

{a: {$exists: true}}

Docs containing an a field.

{a: /foo.*bar/}

Docs where a matches the regular

expression foo.*bar.

{a: {$not: {$type: 2}}}

Docs where a is not a string. $not

negates any of the other query operators.

For More Information

http://docs.mongodb.org/manual/tutorial/query-documents/
http://docs.mongodb.org/manual/reference/operator/query/
Queries

Updates

Updates
Field Update Modifiers

{$inc: {a: 2}}

Increments a by 2.

{$set: {a: 5}}

Sets a to the value 5.

{$unset: {a: 1}}

Deletes the a key.

{$max: { a: 10 } }

Sets a to the greater value, either current

or 10. If a does not exist sets a to 10.

{$min: {a: -10}}

Sets a to the lower value, either current or

-10. If a does not exist sets a to -10.

{$mul: { a: 2 } }

Sets a to the product of the current value

of a and 2. If a does not exist sets a to 0.

{$rename: { a: b} }

Renames field a to b.

{ $setOnInsert: { a: 1 } },
{ upsert: true }

{$currentDate: { a: { $type:
date} } }

Sets field a to 1 in case of upsert

operation.
Sets field a with the current date.
$currentDate can be specified as date
or timestamp. Note that as of 3.0, date and
timestamp are not equivalent for sort order.
Performs the bitwise and operation over
a field:

{ $bit: { a: { and: 7 } } }

1000
0100
------1100
Supports and|xor|or bitwise operators.

Array Update Operators

{$push: {a: 1}}

Appends the value 1 to the array a.

{$push: {a: {$each: [1, 2]}}}

Appends both 1 and 2 to the array a.

{$addToSet: {a: 1}}

Appends the value 1 to the array a (if the

value doesnt already exist).

{$addToSet: {a: {$each: [1,

2]}}}

Appends both 1 and 2 to the array a (if

they dont already exist).

{$pop: {a: 1}}

Removes the last element from the array a.

{$pop: {a: -1}}

Removes the first element from the array a.

{$pull: {a: 5}}

Removes all occurrences of 5 from the

array a.

{$pullAll: {a: [5, 6]}}

Removes multiple occurrences of 5 or 6

from the array a.

For More Information

http://docs.mongodb.org/manual/reference/operator/update/
Updates

Aggregation
Framework

Aggregation Framework
The aggregation pipeline is a framework for data aggregation modeled on the
concept of data processing pipelines. Documents enter a multi-stage pipeline that
transforms the documents into aggregated results. Pipeline stages appear in an array.
Documents pass through the stages in sequence. Structure an aggregation pipeline
using the following syntax:
db.collection.aggregate( [ { <stage> }, ... ] )

Aggregation Framework Stages

{$match: { a: 10 }}

Passes only documents

where a is 10.

Similar to find()

{$project: { a: 1,
_id:0}}

Reshapes each document

to include only field a,
removing others.

Similar to find()
projection

{$project: {
"$a" }}

Reshapes each document

to include only _id and the
new field new_a with the
value of a.

{a:1} =>
{new_a:1}

{$project: { a: {$add:[$a, $b]}}}

Reshapes each document to

include only _id and field
a, set to the sum of a and b.

{a:1, b:10} =>

{a: 11}

{$project: { stats:
{
value: $a,
fraction: {$divide: [$a, $b]}
}
} }

Reshapes each document

to contain only _id and
the new field stats which
contains embedded fields
value, set to the value of a,
and fraction, set to the
value of a divided by b.

{a: 10, b:2} =>

{ stats:{ value:
10, fraction:
5} }

Groups documents by field

a and computes the count
of each distinct a value.

{a:hello},
{a:goodbye},
{a:hello} =>
{_id:hello,
count:2}, {_
id:goodbye,
count:1}

new_a:

{$group: {
_id: $a,
count:{$sum:1}
} }

Aggregation Framework Stages (continued)

{$group: { _id: $a,

names: {$addToSet:
$b}} }

Groups documents by field

a with new field names
consisting of a set of b
values.

{a:1, b:John},
{a:1, b:Mary}
=> {_id:1,
names:[John,
Mary] }

{$unwind: $a}

Deconstructs array field a

into individual documents of
each element.

{a: [2,3,4]} =>

{a:2}, {a:3},
{a:4}

{$limit: 10}

Limits the set of documents

to 10, passing the first 10
documents.

{$sort: {a:1}}

Sorts results by field a

ascending.

{$skip: 10}

Skips the first 10

documents and passes the
rest.

{$out: myResults}

Writes resulting documents

of the pipeline into the
collection myResults.

For More Information

http://docs.mongodb.org/master/core/aggregation-introduction/

Aggregation Framework

Must be the last stage

of the pipeline.

Indexing

Indexing
Index Creation Syntax
db.coll.createIndex(<key_pattern>, <options>)
Creates an index on collection coll with given key pattern and options.

Indexing Key Patterns

{a:1}

Simple index on field a.

{a:1, b:-1}

Compound index with a ascending and b descending.

{a.b: 1}

Ascending index on embedded field a.b.

{a: text}

Text index on field a. A collection can have at most one

text index.

{a: 2dsphere}

Geospatial index where the a field stores GeoJSON

data. See documentation for valid GeoJSON formatting.

{a: hashed}

Hashed index on field a. Generally used with hashbased sharding.

Index options

{unique: true}

Creates an index that requires all values of the

indexed field to be unique.

{background: true}

Creates this index in the background; useful when

you need to minimize index creation performance
impact.

{name: foo}

Specifies a custom name for this index. If not

specified, the name will be derived from the key
pattern.

{sparse: true}

Creates entries in the index only for documents

having the index key.

{expireAfterSeconds:360}

Creates a time to live (TTL) index on the index key.

This will force the system to drop the document after
3600 seconds expire. Only works on keys of date
type.

{default_language:
portuguese}

Used with text indexes to define the default language

used for stop words and stemming.

Examples

db.products.createIndex(
{supplier:1}, {unique:true})

Create ascending index on supplier

assuring unique values.

db.products.createIndex(
{description: text,
{default_language:
spanish})

Creates text index on description key

using Spanish for stemming.

db.products.createIndex( {
regions: 1 }, {sparse:true})

Creates ascending sparse index on

regions key. If regions is an array
e.g., regions: [EMEA, NA,
LATAM] will create a multikey index.

db.stores.createIndex(
{location: 2dsphere})

Creates a 2dsphere geospatial index on

location key.
Indexing

Administration

db.products.getIndexes()

Gets a list of all indexes on the products

collection.

db.products.reIndex()

Rebuilds all indexes on this collection.

db.products.dropIndex({x: 1, y:
-1})

Drops the index with key pattern {x:

1, y: -1}. Use db.products.
dropIndex(index_a) to drop index
named index_a. Use db.products.
dropIndexes() to drop all indexes on
the products collection.

For More Information

http://docs.mongodb.org/master/core/indexes-introduction/

Indexing

Replication

Replication
What is a Majority?
If your set consists of...
1 server, 1 server is a majority.
2 servers, 2 servers are a majority.
3 servers, 2 servers are a majority.
4 servers, 3 servers are a majority.
...

Setup
To initialize a three-node replica set including one arbiter, start three mongod
instances, each using the --replSet flag followed by a name for the replica set.
For example:
mongod --replSet cluster-foo
Next, connect to one of the mongod instances and run the following:
rs.initiate()
rs.add(host2:27017)
rs.add(host3:27017, true)
rs.add() can also accept a document parameter, such as rs.add({_id: 4,
host: host4:27017}). The document can contain the following options:

priority: n

votes: n

Members will be elected primary in order of priority, if

possible. Higher values make a member more eligible to
become a primary. n=0 means this member will never
be a primary.
Assigns a member voting privileges (n=1 for voting,

n=0 for nonvoting).

slaveDelay: n

This member will always be a secondary and will lag n

seconds behind the master.

arbiterOnly: true

This member will be an arbiter.

Setup (continued)

hidden: true

Do not show this member in isMaster output. Use

this option to hide this member from clients.

tags: [...]

Member location description.

See docs.mongodb.org/manual/data-center-awareness.

Administration

rs.initiate()

Creates a new replica set with one member.

rs.add(host:port)

Adds a member.

rs.addArb(host:port)

Adds an arbiter.

rs.remove(host:port)

Removes a member.

rs.status()

Returns a document with information about the state of

the replica set.

rs.conf()

Returns the replica set configuration document.

rs.reconfig(newConfig)

Re-configures a replica set by applying a new replica

set configuration object.

rs.isMaster()

Indicates which member is primary.

rs.stepDown(n)

Forces the primary to become a secondary for n

seconds, during which time an election can take place.

Replication

Administration (continued)

rs.freeze(n)

Prevents the current member from seeking election as

primary for n seconds. n=0 means unfreeze.

rs.printSlaveReplicatio
nInfo()

Prints a report of the status of the replica set from the

perspective of the secondaries.

For More Information

http://docs.mongodb.org/master/core/replication-introduction/

Replication

Sharding

Sharding
sh.enableSharding( products)

Enables sharding on products database.

sh.shardCollection( products.
catalog, { sku:1, brand:1})

Shards collection catalog of products

database with shard key consisting of the
sku and brand fields.

sh.status()

Prints a formatted report of the sharding

configuration and the information regarding
existing chunks in a sharded cluster.

sh.addShard( REPLICA1/
host:27017)

Adds existing replica set REPLICA1 as a

shard to the cluster.

For More Information

http://docs.mongodb.org/master/core/sharding-introduction/

Mapping SQL to
MongoDB

Mapping SQL to MongoDB

Converting to MongoDB Terms
MYSQL Executable

Oracle Executable

MongoDB Executable

mysqld

oracle

mongod

mysql

sqlplus

mongo

SQL Term

MongoDB Term

database (schema)

database

table

collection

index

index

row

document

column

field

joining

linking & embedding

partition

shard

Queries and other operations in MongoDB are represented as documents passed

to find()and other methods. Below are examples of SQL statements and the
analogous statements in MongoDB JavaScript shell syntax.

SQL

MongoDB

CREATE TABLE users (name

VARCHAR(128), age NUMBER)

db.createCollection(users)

INSERT INTO users VALUES

(Bob, 32)

db.users.insert({name: Bob,
age: 32})

SELECT * FROM users

db.users.find()

SELECT name, age FROM users

db.users.find({}, {name: 1,
age: 1, _id:0})

SELECT name, age FROM users

WHERE age = 33

db.users.find({age: 33}, {name:

1, age: 1, _id:0})

SELECT * FROM users WHERE age

> 33

db.users.find({age: {$gt: 33}})

SELECT * FROM users WHERE age

<= 33

db.users.find({age: {$lte:
33}})

SELECT * FROM users WHERE age >

33 AND age < 40

db.users.find({age: {$gt: 33,

$lt: 40}})

SELECT * FROM users WHERE age =

32 AND name = Bob

db.users.find({age: 32, name:

Bob})

SELECT * FROM users WHERE age =

33 OR name = Bob

db.users.find({$or:[{age:33},
{name:Bob}]})

SELECT * FROM users WHERE age =

33 ORDER BY name ASC

db.users.find({age: 33}).
sort({name: 1})

SELECT * FROM users ORDER BY

name DESC
SELECT * FROM users WHERE name
LIKE %Joe%

db.users.find().sort({name:
-1})
db.users.find({name: /Joe/})

Mapping SQL to MongoDB

SQL

MongoDB

SELECT * FROM users WHERE name

LIKE Joe%

db.users.find({name: /^Joe/})

SELECT * FROM users LIMIT 10

SKIP 20

db.users.find().skip(20).limit(10)

SELECT * FROM users LIMIT 1

db.users.findOne()

SELECT DISTINCT name FROM users

db.users.distinct(name)

SELECT COUNT(*) FROM users

db.users.count()

SELECT COUNT(*) FROM users

WHERE AGE > 30

db.users.find({age: {$gt:
30}}).count()

SELECT COUNT(AGE) FROM users

db.users.find({age: {$exists:
true}}).count()

UPDATE users SET age = 33 WHERE

name = Bob

db.users.update({name: Bob},
{$set: {age: 33}}, {multi:
true})

UPDATE users SET age = age + 2

WHERE name = Bob

db.users.update({name: Bob},
{$inc: {age: 2}}, {multi:
true})

DELETE FROM users WHERE name =

Bob

db.users.remove({name: Bob})

CREATE INDEX ON users (name

ASC)

db.users.createIndex({name: 1})

CREATE INDEX ON users (name

ASC, age DESC)

db.users.createIndex({name: 1,
age: -1})

EXPLAIN SELECT * FROM users

WHERE age = 32

SELECT age, SUM(1) AS counter

FROM users GROUP BY age

db.users.find({age: 32}).explain()
(db.users.explain().find({age:
32}) for 3.0)
db.users.aggregate( [ {$group:
{_id: $age, counter:
{$sum:1}} } ])

Mapping SQL to MongoDB

SQL

MongoDB

SELECT age, SUM(1) AS counter

FROM users WHERE country = US
GROUP BY age

db.users.aggregate([
{$match: {country: US} },
{$group: {_id: $age,
counter: {$sum:1}} }
])

SELECT age AS how_old FROM

users

db.users.aggregate( [
{$project: {how_old:
$age}}
])

For More Information

http://docs.mongodb.org/manual/reference/sql-comparison/

Mapping SQL to MongoDB

Resources
Learn
Downloads - mongodb.org/downloads
Enterprise Advanced - mongodb.com/enterprise
MongoDB Manual - docs.mongodb.org
Free Online Education - university.mongodb.com
Presentations - mongodb.com/presentations
In-person Training - university.mongodb.com/training
Support
Stack Overflow - stackoverflow.com/questions/tagged/mongodb
Google Group - groups.google.com/group/mongodb-user
Bug Tracking - jira.mongodb.org
MongoDB Management Service - mms.mongodb.com
Commercial Support - mongodb.com/support
Community
MongoDB User Groups (MUGs) - mongodb.com/user-groups
MongoDB Events - mongodb.com/events
Social
Twitter - @MongoDB, @MongoDB_Inc
Facebook - facebook.com/mongodb
LinkedIn - linkedin.com/groups/MongoDB-2340731
Contact
Contact MongoDB - mongodb.com/contact

2015 MongoDB Inc.

For more information or to download MongoDB, visit mongodb.org