'Connect' a rails app to an already existing MySQL DB?

Question

So in my company we are slowly moving to Rails instead of PHP(Code Igniter to be precise). So, our actual PHP App is using a Mysql DB and I\'d like to connect a new Rails ap

Answer 1

There are two aspects of a Rails app to consider for this scenario:

1: the database connection

Simply put the credentials for this database into database.yml.

A model like "User" will by default attempt to find records and attribute definitions in a table called "users". ActiveRecord will assume there's an auto-incrementing integer primary key on each table. When saving records, it will attempt to write to columns called created_at and updated_at. Those are a few things to be mindful of when making and using the connection.

2: the database migrations

Rails uses migration files to manage a sequence of changes to the database structure. Under normal conditions, someone building a Rails app will be starting with an empty database.

In the case of an existing database, I would recommend making a migration something like:

class BuildLegacyDbStructure < ActiveRecord::Migration  
  def up
    Mysql2.connection.execute_some_sql_file(  # made-up function
      Rails.root.join('path', 'to', 'file')
    )  
  end

  def down
    # reverse those changes; bring DB down to blank state
  end
end  

Another option would be to disable Rails/ActiveRecord's migration-based management of the database entirely. For example Rails will generate a migration when you generate a new model. So if you have an existing users table in your PHP app, and you'd like to make a rails model to use this table, you'd run something like rails generate model User --no-migration.