NOTE: data wasn’t migrated in this guide. Instead we changed database from Postgresql to SQLite3. …

Usually it’s the other way around, right? Migrating from the default SQLite database to a more industry standard for production, Postgresql. But I’ve been going through the free React on Rails course and per usual my app’s behavior veers from the demonstrated behavior. I suspect that the difference could be due to my using Postgresql instead of the default SQLite. So let’s learn how to migrate a database!

As expected, all the Google results are about migrating the other way, so let’s fiddle and observe. I’m going to make a newbie move and just change my Gemfile, run bundle install, and then rails server. Here’s the relevant snippet from my Gemfile and the corresponding error in the browser:

# gem 'pg', '~> 0.18'
gem 'sqlite3'
No connection pool with 'primary' found.

The Stack Overflow thread I found hints at the config/database.yml file. So let’s change that to be more SQLite-y.

  adapter: sqlite3
  database: db/development.sqlite3
  pool: 5
  timeout: 5000
  adapter: sqlite3
  database: db/test.sqlite3
  pool: 5
  timeout: 5000
  adapter: sqlite3
  database: db/production.sqlite3
  pool: 5
  timeout: 5000

Running rails server gives us a new error now:

Migrations are pending. To resolve this issue, run: bin/rails db:migrate RAILS_ENV=development

So let’s run rails db:migrate:

== 20170802165856 CreateAppointments: migrating ===============================
-- create_table(:appointments)
   -> 0.0015s
== 20170802165856 CreateAppointments: migrated (0.0016s) ======================

Ok, now running rails server gives us the form as expected. Looking forward, I would want to actually migrate the data because at this point it’s all gone. That’s something I’ve just learned and should be mindful of when data is crucial.

And after entering data into the form, per section 3.1 of the React on Rails guide, I still get the behavior I observed before. So maybe it wasn’t a Postresql database issue. At least we can better appreciate where the database dependencies live: Gemfile, config/database.yml, and then running rails db:migrate.