Database Migrations with micrate

If you're using Granite to query your data, you likely want to manage your database schema as well. Migrations are a great way to do that, so let's take a look at micrate, a project to manage migrations. We'll use it as a dependency instead of a pre-build binary.

Install

Add micrate your shards.yml

dependencies:
  micrate:
    github: juanedi/micrate

Update shards

$ shards update

Create an executable to run the Micrate::Cli. For this example, we'll create bin/micrate in the root of our project where we're using Granite ORM. This assumes you're exporting the DATABASE_URL for your project and an environment variable instead of using a database.yml.

#! /usr/bin/env crystal
#
# To build a standalone command line client, require the
# driver you wish to use and use `Micrate::Cli`.
#
​
require "micrate"
require "pg"
​
Micrate::DB.connection_url = ENV["DATABASE_URL"]
Micrate::Cli.run

Make it executable:

$ chmod +x bin/micrate

We should now be able to run micrate commands.

$ bin/micrate help => should output help commands.

Creating a migration

Let's create a posts table in our database.

$ bin/micrate create create_posts

This will create a file under db/migrations. Let's open it and define our posts schema.

-- +micrate Up
-- SQL in section 'Up' is executed when this migration is applied
CREATE TABLE posts(
  id BIGSERIAL PRIMARY KEY,
  title VARCHAR NOT NULL,
  body TEXT NOT NULL,
  created_at TIMESTAMP,
  updated_at TIMESTAMP
);
​
-- +micrate Down
-- SQL section 'Down' is executed when this migration is rolled back
DROP TABLE posts;

And now let's run the migration

$ bin/micrate up

You should now have a posts table in your database ready to query.