Slick Exercises

Examples and exercises for Essential Slick.

Licensed Apache 2.0.

Overview

There are two Scala projects in this repository:

• example - A small example app that connects to an H2 in-memory database.

• exercise - An almost-empty project that connects to a MySQL database. Most exercises in the course will involve writing code here to query and update this database.

Docker

The exercise project uses Docker to ensure a consistent environment. There is a docker-compose.yml file that configures two containers:

• app - A container for your Scala code:

  • Has SBT, Scala, and a JVM pre-installed.
  • Has /root mapped to the repository root.
  • You can shell into it and run sbt.
  • It has network access to the database container to connect to MySQL...

• database - A MySQL container:

  • Has a database called employees.
  • Has two users - dbuser and root - both with the password password.
  • Has /var/lib/mysql mapped to ./mysql/docker-data so your data is persisted between runs.

Sample Data

I've included a load of sample data from a dummy employee database in ./sample-data. This is mapped to /sample-data in the database container. There's a script called ./sample-data/import-data.sh that you can run from inside the database container to recreate the employees database. See below for more information.

Getting Started

You'll need:

• Scala/SBT/JVM
• Docker
• An editor (IntelliJ IDEA or VSCode will do)

Start by cloning the repo:

git clone https://github.com/spacecatio/slick-exercises
cd ./slick-exercises

Check your basic Scala and Slick setup by running the example project. This will take a couple of minutes the first time you run it:

sbt example/run
# ... lots of output ...
#
# [info] running code.Main
# Album(Keyboard Cat,Keyboard Cat's Greatest Hits,2009,5,3)
# Album(Pink Floyd,Dark Side of the Moon,1978,5,5)
# Album(Daft Punk,Alive 2007,2007,4,1)
# Album(Spice Girls,Spice,1996,4,7)
# Album(Rick Astley,Whenever You Need Somebody,1987,3,6)
# [success]

Now check your Docker setup by starting the Docker containers. This will take a couple of minutes the first time you run it:

docker compose up --wait --detach

Connect to the database container and run a handy script to set up some sample data. This will take about a minute:

docker compose exec database bash
cd /sample-data/
./import-data.sh
# IMPORTING DATA
#
# ... lots of output ...
#
# ALL DONE! EMPLOYEE COUNT IS BELOW
#
# +----------+
# | count(*) |
# +----------+
# |   300024 |
# +----------+

Press Ctrl+D to exit the container and return to your own computer's shell.

Finally, run the exercise project and check that Scala can connect to the database:

docker compose exec app sbt
exercise/run
# ... lots of output ...
#
# Yay! There are 300024 employees in the database!

Useful Commands

The following commands all assume you're in the repository root directory:

Starting and Stopping Containers

# Start containers, wait until press Ctrl+C, stop containers, return to shell:
docker compose up

# Start containers, wait until started, return to shell while containers still running:
docker compose up --wait --detach

# Stop containers, wait until stopped, return to shell:
docker compose down

Accessing Containers

# Run an interactive SBT on the `app` container:
docker compose exec app sbt

# Run an interactive shell on the `app` container:
docker compose exec app bash

# Run an interactive shell on the `database` container:
docker compose exec database bash

Accessing the Database

When running a shell in the app container:

# Connect to the database:
mysql --host=database --database=employees --user=dbuser --password=password

When running a shell in the database container:

# Connect to the database:
mysql --host=database --database=employees --user=dbuser --password=password

# Recreate the employee database:
/sample-data/import-data.sh

Interrogating the Database

At a MySQL prompt:

-- List the tables in the database
show tables;

-- Show the schema of a table
desc employees;

-- Regular SQL works, obviously
select * from employees limit 10;

Connecting to the Database from Outside of Docker

The database server is externally visible on the host machine as localhost:33060. You can access it with the following command:

mysql --host=localhost --port=33060 --protocol=tcp --database=employees --user=dbuser --password=password

You can use this in tools like DataGrip to get an overview of the employee database:

• Host: localhost
• Port: 33060
• Database: employees
• User: dbuser
• Password: password
• JDBC URL: jdbc:mysql://localhost:33060/exercises