Introduction

We are starting an adventure: we are going to build agreat-outstanding-marvelous application using theCrystal language!

But, since these are our first steps using the Crystal language, maybe we could start with a firstsimple app? 🤔 Yeah! It sounds good! So, this is the goal for this post:3 steps for creating asimple app using Crystal! 🚀

1, 2, 3 … Hold it! We are assuming that you already have installed the Crystal language. But, what if you didn't? 😱

Well, in that case here it isstep 0: 

• Go to the Crystal language site and click onInstall. There you'll find all you need to install the language compiler for your platform ... don't worry, we'll wait for you ...

and anotherstep 0 😝:

• In theoverview section, you will find some great examples if you didn't use Crystal before.

⏰a few minutes later

Are you ready? Great! Let's start!

Step 1:init is the magic word

So, first things first: assuming that our app is calledmy_app (if you can think of a better name, go ahead and rename it! 🙃) then we create the application using the same Crystal's command line, like this:

$crystal init app my_app

And Crystal will reply:

create  my_app/.gitignore   create  my_app/.editorconfig   create  my_app/LICENSE   create  my_app/README.md   create  my_app/.travis.yml   create  my_app/shard.yml   create  my_app/src/my_app.cr   create  my_app/spec/spec_helper.cr   create  my_app/spec/my_app_spec.crInitialized empty Git repository in /great_projects/my_app/.git/

Perfect! We have the project with the Git repository already initialized and with a basic.gitignore (thanks Crystal! ❤️)

In the foldermy_app/src/my_app.cr we have the entry point to our application. Although we may use other file, it is a standing point to start building our app.

Step 2: Helloworld database!

Not the Hello World example! Withstep 1 we have a new Crystal App ready to grow! So let's continue with a more interesting example ... maybe we could connect to a database? Yeah! Let's do that!

We'll be using a MySQL database, It won't be necessary to install the database in our computer, instead we could use aDockercontainer! Here's thedocker-compose.yml file:

version:'3'services:db:image:mysql:8.0.17command:--default-authentication-plugin=mysql_native_passwordrestart:alwaysenvironment:MYSQL_ROOT_PASSWORD:rootcontainer_name:crystal_dbports:-3306:3306volumes:db:

Great! With this, we may start the container and have a MySQL database ready for us to use!

Let's start the container:

$docker-compose up

If it's all good, then the response from docker should end with something like this:

crystal_db | Socket: '/var/run/mysqld/mysqlx.sock' bind-address: '::' port: 33060

Now, using our favourite database tool (in my case I'm usingTablePlus), we may connect to the database using this configuration:

host:127.0.0.1port:3306user:rootpassword:root

And last (but not least) we will create a new database for our project calledcrystal123_db

CREATEDATABASE`crystal123_db`;USE`crystal123_db`;

Step 3: (Actually) using the database from our app!

And here we are, the final step! We will need the correspondingMySQL-connector in order to use the database from our Crystal app.

First, we need to add the mysql-shard in our application'sshard.yml file, like this:

dependencies:mysql:github:crystal-lang/crystal-mysql

And then, we install all the dependencies with:

$shardsinstall

Shards will reply:

Fetching https://github.com/crystal-lang/crystal-mysql.gitFetching https://github.com/crystal-lang/crystal-db.gitInstalling mysql (0.10.0)Installing db (0.8.0)

Note:Shards is theDependency manager for the Crystal language.

Now, let's try toconnect to the database! (remember we called the database:crystal123_db ... a great name if you ask me 😎) And, since we are there, we willcreate a new table calledbank_accounts (with to columns:name andamount)

# my_app.crrequire"mysql"db=DB.open"mysql://root:root@localhost/crystal123_db"db.exec"drop table if exists bank_accounts"db.exec"create table bank_accounts (name varchar(30), amount int)"

Let's run the code using Crystal's command line:

$crystal ./src/my_app.cr

Go to the database ... yes! The tablebank_accounts was created!!

And for the same price, let'sadd 2 rows to the table. Here is the final version ofmy_app.cr:

# my_app.crrequire"mysql"db=DB.open"mysql://root:root@localhost/crystal123_db"db.exec"drop table if exists bank_accounts"db.exec"create table bank_accounts (name varchar(30), amount int)"# first rowdb.exec"insert into bank_accounts values (?, ?)","John",100# second rowdb.exec"insert into bank_accounts values (?, ?)","Sarah",250

We run the application:

$crystal ./src/my_app.cr

Let's check the database and ... yes! Now we have the tablebank_accounts created and with 2 rows! We did it! 🎉

Farewell and see you later

We have reached the end of this first journey. To recap:

• we have initialized a Crystal application using the command line.
• we have installed a database (actually a container with the database)
• and finally we have use the database from our Crystal application!

Hope you enjoyed it! Until the nextCrystal adventure!😃

References:

• Using the Crystalcompiler
• Using adatabase with Crystal.
• Theshards command