MongoDB 101: A Starter Guide

MongoDB

Open source document database

I. Definitions

A. Document

• Represent one record in MongoDB; consists of key-value pairs.

• Similar to JSON Objects

• Values may include other documents, arrays, or arrays of documents

   {
       "_id" : ObjectId("54c955492b7c8eb21818bd09"),
       "student_number" : "2010-30010",
       "last_name" : "Dela Cruz",
       "first_name" : "Juan",
       "middle_name" : "Masipag",
       "address" : {
           "street" : "#35 Maharlika St.",
           "zipcode" : "30011",
           "city" : "Quezon City",
           "coord" : [ -73.9557413, 40.7720266 ]
       },
       "gwa" : "1.75",
       "program" : "Computer Science",
       "degree" : "Bachelor of Science"
   }
  

B. Collection

Documents are stored in collections. They are similar to tables but unlike a table, a collection does not require documents to have the same schema.

Documents stored in a collection has a unique identifier _id that acts as the primary key.

II. Installation

A. Mac OSx

brew install mongodb

B. Ubuntu

sudo apt-key adv --keyserver hkp://keyserver.ubuntu.com:80 --recv EA312927

echo "deb http://repo.mongodb.org/apt/ubuntu trusty/mongodb-org/3.2 multiverse" | sudo tee /etc/apt/sources.list.d/mongodb-org-3.2.list

sudo apt-get update

sudo apt-get install -y mongodb-org

III. Setup

A. Running the Database

By default, mongod looks for your database at /data/db

 mongod

In case your database is at a different path, provide the –dbpath parameter

 mongod --dbpath .

B. Running the Console

 mongo

By default, Mongo console would connect to localhost at port 27017. Make sure that mongod is running before you issue the mongo command.

C. Switching database

use mongo-cheatsheet
# switched to db mongo-cheatsheet; would be created if non existent

III. CRUD Operations

A. Insertion

db.students.insert(
  {
     "student_number" : "2010-30010",
     "last_name" : "Dela Cruz",
     "first_name" : "Juan",
     "middle_name" : "Masipag",
     "address" : {
       "street" : "#35 Maharlika St.",
       "zipcode" : "30011",
       "city" : "Quezon City",
       "coord" : [ -73.9557413, 40.7720266 ]
     },
     "gwa" : 1.75,
     "course" : "BS Computer Science"
  })
  
 # => WriteResult({ "nInserted" : 1 })
 
 # _id is automatically asssigned

B. Read or Lookup

# Find student with student_number 2010-30010
db.students.find( { "student_number": "2010-30010" } )

# Find student with zipcode (embedded attribute) 30011
db.students.find( { "address.zipcode": "30011" } )

# Find students with the gwa column greater than 1.25
db.students.find( { "gwa": { $gt: 1.25 } } )

# Find students with the gwa column less than 1.25 and course is BS Computer Science
db.students.find( { "gwa": { $lt: 1.25 } , "course": "BS Computer Science"} )

# Find students with the gwa column less than 1.25 or course is Computer Science
db.students.find( { $or: [{ "gwa": { $lt: 1.25 } } , {"course": "BS Computer Science"}]})

C. Update

i. Update Attribute/s

Updates first matching document with first_name: Juan

db.students.update(
    { "first_name" : "Juan" },
    {
        $set: { "first_name": "Juana" }
    }
)

The following code snipper updates the first matching document with first name Juan. And also sets the field lastModified to true (since it is non existent on the first run based on our schema, it will be created and set.)

db.students.update(
    { "first_name" : "Juan" },
    {
        $set: { "first_name": "Juana" },
        $currentDate: { "lastModified": true }
    }
)

ii. Update Embedded Fields

db.students.update(
    { "first_name" : "Juana" },
    { $set: { "address.street": "#45 Maginhawa St.",
              "address.city": "Quezon City" }}
)

iii. Updating All Matching Documents

By default, update only updates the first matching document. To tell MongoDB to update all matching, we pass multi: true

db.students.update(
  { "first_name" : "Juan" },
  { $set: { "address.street": "East 31st Street" } },
  { multi: true}
)
# WriteResult({ "nMatched" : 2, "nUpserted" : 0, "nModified" : 2 })

iv. Replace

db.students.update(
    { "first_name" : "Juan" },
    {
        "first_name" : "Victoria",
        "address" : {
            "street" : "Emerson Subdivision",
            "city" : "Saog, Marilao"}
    }
)

If you want to insert in case the data is non-existent, pass upsert: true as well to the update call.

{ upsert: true }

D. Delete

i. Delete a document

db.students.remove( { "first_name": "Juan" } )
# removes all document

db.students.remove( { "first_name": "Victoria" }, { justOne: true } )
# removes only one of the matching document     

ii. Drop a Collection

db.students.drop
# => true

IV. Query

In addition to simple lookup commands, you can also use aggregation:

db.students.aggregate(
[
 { $group: { "_id": "$address.city", "count": { $sum: 1 } } }
]
);

Other available operators:

• sort
• project
• and many more…

V. Data Import

A. Import from JSON, CSV, TSV

To import dataset from a JSON, CSV, or TSV

mongoimport --db mongo-cheatsheet --collection students --drop --file primer-dataset.json

Where:

• Database name: mongo-cheatsheet
• Collection name: students
• Source File: primer-dataset.json

By default, connects to localhost:27017. If you wish to connect to other ports, add flags: –host and –port

mongoimport --db mongo-cheatsheet --collection students --drop --file primer-dataset.json --host 192.168.123.321 --port 27019

B. Restore from Mongo Backup

To restore from a mongoDB backup:

mongorestore --drop --db mongo-cheatsheet /path/to/your/dump

Where:

• Database name: mongo-cheatsheet
• Dump path: /path/to/your/dump

C. Backup a Mongo Database

mongodump --db mongo-cheatsheet

• Database name: mongo-cheatsheet