It is essential to make sure that the connection to your database is correct in any application that you are developing with database capabilities. To check database connection in Ruby you have to go through several steps that can differ depending on the DBMS you are using and the libraries or frameworks you include into your project. This article will help you check a database connection in Ruby with examples involving the most commonly used database management systems such as PostgreSQL, MySQL, and SQLite, whether you are using plain Ruby or Ruby on Rails.

1. Checking Database Connection in Plain Ruby

For a plain Ruby application, you will likely use a database adapter gem to manage the connection. Here’s how to do it with some common DBMS:

PostgreSQL

To connect to a PostgreSQL database, you can use the pg gem. First, ensure the gem is installed:

gem install pg

Here’s a sample script to check the connection:

require 'pg'

begin
  conn = PG.connect(
    dbname: 'your_database_name',
    user: 'your_username',
    password: 'your_password',
    host: 'your_host',
    port: 'your_port'
  )
  puts 'Connection to the database established successfully.'
  conn.close
rescue PG::Error => e
  puts "An error occurred: #{e.message}"
ensure
  conn.close if conn
end

MySQL

For MySQL, you can use the mysql2 gem. First, install the gem:

gem install mysql2

Then, use the following script to check the connection:

require 'mysql2'

begin
  client = Mysql2::Client.new(
    host: 'your_host',
    username: 'your_username',
    password: 'your_password',
    database: 'your_database_name'
  )
  puts 'Connection to the database established successfully.'
  client.close
rescue Mysql2::Error => e
  puts "An error occurred: #{e.message}"
ensure
  client.close if client
end

SQLite

SQLite is a self-contained, serverless database engine. You can use the sqlite3 gem. Install it first:

gem install sqlite3

Here’s how to check the connection:

require 'sqlite3'

begin
  db = SQLite3::Database.new 'your_database_file.sqlite3'
  puts 'Connection to the database established successfully.'
  db.close
rescue SQLite3::Exception => e
  puts "An error occurred: #{e.message}"
ensure
  db.close if db
end

2. Checking Database Connection in Ruby on Rails

Ruby on Rails abstracts much of the direct database connection handling through ActiveRecord. Here’s how you can check the database connection in a Rails application.

PostgreSQL, MySQL, and SQLite

Rails uses the database.yml file to manage database configurations. To check the database connection, you can run a simple rake task or script.

# lib/tasks/db_check.rake
namespace :db do
  desc 'Check database connection'
  task check_connection: :environment do
    begin
      ActiveRecord::Base.connection
      puts 'Connection to the database established successfully.'
    rescue ActiveRecord::NoDatabaseError => e
      puts 'Database does not exist.'
    rescue ActiveRecord::ConnectionNotEstablished => e
      puts 'Connection to the database could not be established.'
    rescue StandardError => e
      puts "An error occurred: #{e.message}"
    end
  end
end

To run this task, use the command:

rake db:check_connection

This task will load the Rails environment, attempt to establish a connection to the database, and output the status.