An Introduction to MongoDB

Instructions

Fork and clone this repository.

Objectives

By the end of the lesson, students should be able to:

Use the MongoDB shell to interact with MongoDB databases and collections
Create, Read, Update, and Delete documents in MongoDB collections using the MongoDB shell.

Prerequisites

Basic JavaScript.

Required readings:

Installation

We'll run brew install mongodb then to make sure we're up to date run brew update then brew upgrade mongo.

On Ubuntu

Run sudo apt-get install mongodb

Introduction

Relational databases are good at modeling data that fits into tables. What do you use if your data isn't that structured?

Perhaps a noSQL data-store.

MongoDB is a schema-less document-store that organizes documents in collections. What does this mean?

Terminology

Relational Database Term	MongoDB Term
database	database
table	collection
row	document
column	field

Create a database

Code along

We'll use mongo-crud as the database to hold our tables and mongo to interact with it. mongo is MongoDB's command line client which lets us execute commands interactively and from scripts.

First let's fire up our server:

brew services start mongodb

$ mongo mongo-crud
MongoDB shell version: 3.2.10
connecting to: mongo-crud
>

The command to list databases is show databases (or show dbs):

> show databases
local  0.000GB # or local  0.078GB
>

Unlike PostgreSQL, MongoDB lets us select a database that hasn't been created. When we add a collection, the database will be created.

If we didn't specify the database on the command line we can connect to a database with use <database name>:

MongoDB shell version: 3.2.10
connecting to: test
> use mongo-crud
switched to db mongo-crud
> show databases
local  0.078GB
>

Create a Collection

Code Along

Our first collection will be called people. It has no entries.

> show collections
> db.people.count();
0

This is a common pattern in MongoDB: you can refer to things that don't yet exist, and it will cooperate. MongoDB won't create them until you give it something to remember.

Adding a document to a collection

Inserting data - Overview of adding documents to a collection.
db.collection.insert() - detailed documentation of MongoDB's insert collection method.
Importing data - overview of MongoDB's mongoimport command line utility.
mongoimport - detailed documentation of MongoDB's mongoimport command line utility.

MongoDB's mongoimport command will let us load bulk data from a JSON or CSV file.

Demo: Bulk Load Books

Watch as I load data in bulk from data/books.csv. We'll save the command in scripts/import/books.sh.

mongoimport --db=mongo-crud --collection=books --type=csv --headerline --file=data/books.csv

Code along: Bulk Load People

First we'll load data in bulk from data/people.csv. We'll save the command in scripts/import/people.sh.

mongoimport --db=mongo-crud --collection=people --type=csv --headerline --file=data/people.csv

If we want to clear the collection before the import, we pass the --drop flag.

Run this script by typing:

sh path_to_file.sh

Now that we've inserted data into it, the mongo-crud database and the people collection both exist.

$ mongo mongo-crud
MongoDB shell version: 3.2.10
connecting to: mongo-crud
> show dbs
local       0.078GB
mongo-crud  0.078GB
> show collections
people
system.indexes
> db.people.count();
2438

Next we'll use the insert collection method to add a few more people. We'll save our invocations in insert/people.js. We'll execute that script using the mongo load method. Let's give these people a middle_initial or a nick_name. Note that the attributes we choose for these people need not match those from the data we loaded in bulk.

> load('scripts/insert/people.js');

MongoDB uses JSON natively (technically BSON), which makes it well suited for JavaScript applications. Conveniently, MongoDB lets us specify the JSON as a JavaScript object.

Code along: Insert Doctors

Together we'll add a few doctors then we'll bulk load data/doctors.csv.

Lab: Insert Ingredients

Add an ingedient to the ingredients collection using insert then bulk load data/ingredients.csv.

Retrieving documents from a collection

Querying - Overview of retrieving data from MongoDB.
Queries - More detailed overview on retrieving data.
find - Detailed documentation on the find collection method.
findOne - Detailed documentation on the findOne collection method.
Data aggregation - Overview of summarizing documents.
aggregate - Detailed documentation on the aggregate collection method.

Demo: Read Books

Let's see some what we can learn about the books in the database.

> db.books.find({author: "Ernest Hemingway"}).pretty()
{
    "_id" : ObjectId("583ee3f3e6ae0faa5547068e"),
    "title" : "A Farewell to Arms",
    "author" : "Ernest Hemingway",
    "published_on" : "1986-02-15"
}
{
    "_id" : ObjectId("583ee3f3e6ae0faa5547071a"),
    "title" : "The Sun Also Rises",
    "author" : "Ernest Hemingway",
    "published_on" : "2002-10-20"
}
> db.books.find({published_on: /20/}).count()
36
> db.books.find({published_on: /20/}).sort({title: -1}).limit(2).pretty()
{
    "_id" : ObjectId("583ee3f3e6ae0faa5547072f"),
    "title" : "Wide Sargasso Sea",
    "author" : "Jean Rhys",
    "published_on" : "2011-01-14"
}
{
    "_id" : ObjectId("583ee3f3e6ae0faa55470725"),
    "title" : "Trader",
    "author" : "Charles de Lint",
    "published_on" : "2003-06-23"
}

Note: When using the REPL the .pretty() method can be quite helpful.

What do we see?

MongoDB gave each of our documents a unique ID field, called _id.
MongoDB doesn't care that some documents have fewer or more attributes.

Code along: Read People and Doctors

Together we'll build a query to our people collections table. Let's see if we can find all people born after a date. How about the number of people under 5 feet tall, and doctors who perform surgery?

Lab: Read Ingredients

Write a query to get all the ingredients of unit of tbs.

Changing the data in documents in a collection

Updating Data - overview of changing documents
update - detailed documentation of MongoDB's update collection method.
Update Operators - The different modifications we can make during an update.

Demo: Update Books

MongoDB makes it easy to add an array of items to a document. We'll update some books and give them a correct published_on value.

> db.books.update({title: 1984}, {$set: {"published_on": "1949-06-08"}})
WriteResult({ "nMatched" : 1, "nUpserted" : 0, "nModified" : 1 })
> db.books.update({title: "Slaughterhouse-Five"}, {$set: {published_on: "1969-03-31", book_cover: "brown", pages: 247} })

What happens if we run an update command without the $set option?

Code along: Update People and Doctors

Now, let's update some people with a hometown. Let's update some doctors specialty.

Lab: Update Ingredients

Update a couple of ingredients units.

Deleting documents

Removing Data - Overview of removing documents from a collection.
remove - detailed documentation of MongoDB's remove collection method.

If we want to clean up, db.<collection>.drop(); drops the specified collection and db.dropDatabase(); drops the current database.

Demo: Delete Books

We'll remove a few books from the data-store. There are methods for removing one and multiple entries.

> db.books.deleteOne({author:"Mongo Expert"})
WriteResult({ "nRemoved" : 1 })
> db.books.deleteOne({author:"Mongo Expert"})
WriteResult({ "nRemoved" : 3 })

Code along: Delete People and Doctors

Let's remove all the people with a specific bornOn date and doctors with Internal Medicine as their specialty

Lab: Delete Ingredients

Remove Ingredients that have ml as their unit of measure.

Additional resources

BSON Types

License

All content is licensed under a CCBYNCSA 4.0 license.
All software code is licensed under GNU GPLv3. For commercial use or alternative licensing, please contact legal@ga.co.

ga-wdi-boston / mongodb-crud

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