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MongoDB

Projected Time

4 - 5 hours

  • 20-30 minutes for Lesson
  • 20 minutes for Guided Practice
  • 120 - 180 min for Independent Practice
  • 15 minutes for Challenge
  • 15 minutes for Check for Understanding

Prerequisites

Motivation

Not all data can be or should be stored in a relational way. In those cases, it is more efficient to use a NoSQL database. MongoDB is one of the most popular NoSQL databases. MongoDB stores data in JSON-like "documents," which is familiar to folks who use JavaScript.

Objectives

Participants will be able to:

  • Set up MongoDB on their laptops
  • Create databases and collections in MongoDB
  • Add, query, and update documents

Materials

Lesson

MongodDB (video walkthrough of slides)

MongoDB (slides)

Common Mistakes / Misconceptions

  • "I already learned how to use relational databases. I'll just stick with that. They both store data anyway." The structure of relational databases is set up for relational data. Using a relational databse for non-relational data results in reduced scalability and added cost.

Guided Practice

Techtonica staff will assign pairs.

Activity 1: Installation

  1. Check to see if you have Homebrew installed on your laptop. From your Terminal, run the brew help command. If you have Homebrew installed, you'll see output from Homebrew appear in your Terminal.

If no Homebrew-related text appears, you'll need to install Homebrew. Go to the Homebrew website and follow the installation instructions. Ask for help if needed.

  1. To ensure you have the latest version of MongoDB, run brew update in the Terminal. This may take a couple minutes.

  2. Install MongoDB using brew install mongodb in the Terminal. If you get an error message saying you need to install Xcode from the App Store, follow the instructions to do so and then re-try brew install mongodb. Ask for help if needed.

  3. MongoDB will store data in a directory called /data/db. Check if you have the directory /data/db. If not, run sudo mkdir -p /data/db. If this doesn't work, then try brew services start mongodb

  4. Run whoami to find your username. For example, if your username is "myname", then you will run the following command sudo chown myname /data/db. You may need to enter your password.

  5. If a ~/.bash_profile exists, open it. If not, create one by touch .bash_profile. Open your .bash_profile in your text editor and copy the following into the file:

  • export MONGO_PATH=/usr/local/mongodb
  • export PATH=$PATH:$MONGO_PATH/bin
  1. Save .bash_profile and restart Terminal.
  • Open 2 Terminal windows. On one, run mongod. Wait until the following message appear: [initandlisten] waiting for connections on port 27017. "mongod" stands for Mongo Daemon, the host process for the database. Next, you will open a Mongo shell to access the database.
  1. Keep the first window open with mongod still running. Switch to second terminal window, run mongo --host 127.0.0.1:27017. This is your Mongo shell.

Activity 2: Working with Database

  • The command use <db> sets the current database you'll be working with. In the shell, run use techtonica. Then run show dbs, which will list out the list of databases. What database is there? What is missing?

  • The newly created database, "techtonica", should be missing. This is because the techtonica database is empty. Let's insert some data storing people's name (as a string) and birth month (as an integer). Insert a document by running db.classmates.insert({"name": "your_name", "month": your_birthmonth}). Do it at least two more times with a friend's name. Remember not to double-quote the birth month to keep it as a digit instead of string.

  • Type show dbs again and see that the techtonica database now shows up.

  • MongoDB stores documents in collections. Run show collections. What is already there? Where did it come from?

  • Run db.createCollection("volunteer").

  • View what's in each collection by running db.classmates.find() and db.volunteers.find(). What's the difference?

  • Fix the empty volunteer collection by entering a document: db.volunteers.insert({"volunteer": "Adrien"}) and db.volunteers.insert({"volunteer": "Jamie"}).

  • Now we'll try out the remove command. Select a number between your birth month and your pair's birth month inside the classmates collection. Run db.classmates.remove({"month": {$lt: the_number_your_selected}}). The "$lt" means "less than." What do you think happened to the collections?

  • Run db.classmates.find(). Were you correct?

  • Run db.volunteers.remove({}), then db.volunteers.find(). What happened?

  • Make sure you are in the techtonica database by running use techtonica. Make sure the output is switched to db techtonica. Then, you will delete the techtonica database by running db.dropDatabase(). The output should be { "dropped" : "techtonica", "ok" : 1 }.

  • Exit the shell by running exit. Next, go to the Terminal window running the Mongo Daemon, mongod. Exit the daemon by entering Ctrl C.

Independent Practice

  1. Read through these mongodb docs from TutorialsPoint. You don't have to memorize it, but think about how MongoDB compares to SQL as you read.
  1. Follow this video tutorial for building a full Mongo project on your machine with an mLab online mongo database. This will take at least 2 hours, so settle in! If you don't feel confident that you understand the parts of the project he is going over, stop the video and look up more examples.

Challenge

"$lt" was used earlier to filter out which documents you deleted. MongoDB's documentation has a page on Operators. What type of operator is "$lt"?

Operators can be used to only filter what you remove, or what you find. For example, db.classmated.find({"month": {$lt: 6}}) will output anyone born before July (if you set your_birthmonth "July" as 6; because January is 0 in DateTime). You will be testing some of it next.

Open up the MongoDB daemon and shell again, create a database named "filterData". Create a collection named "zoo". Create at least 3 documents in the following format: {"type": "lion", "name": "Suzy", "age": 10}. Look at MongoDB's Operator page and find at least one operator other than Comparison Operator (which $lt was), and then test it out in the zoo collection.

Check for Understanding

List out the steps to store data in MongoDB. Find a classmate. One of you will try to explain the steps by comparing it to organizing books, and the other will compare it to organizing kitchen utensils.

Supplemental Materials