ActiveRecord with Ruby alone

Active Record is the main tool that Rails developers use to communicate with and underlying database. Active Record does some wonderful things for a web developer looking for abstractions in database setup, SQL connections and queries. We can get a cool command line Ruby application or utility script for our daily tasks using Active Record going in about 5 minutes!

First of all, get the activerecord gem using

  gem install activerecord

At the top of Ruby program we need to require the Active Record gem previously installed. Interacting with your database will be a pleasure now!

  require 'activerecord'

Establishing a connection to database

  ActiveRecord::Base.establish_connection {
    adapter:  "mysql",
    host:     "localhost",
    username: "root",
    password: "password",
    database: "dbname"
  }

After successfull database connection we can create a class that inherits from ActiveRecord::Base whose objects map to database a table. Suppose we have users table with name field:

  class User < ActiveRecord::Base
    # this maps database table "users" to this Ruby class User
  end

  User.all # select all from users table
  usr = User.first # returns the first object fetched by SELECT * FROM users
  usr.name = 'zappy'
  usr.save # name zappy is set for usr and saved in db

Active Record objects don’t specify their attributes directly, but rather infer them from the table definition with which they’re linked. Adding, removing, and changing attributes and their type is done directly in the database. Any change is instantly reflected in the Active Record objects. The mapping that binds a given Active Record class to a certain database table will happen automatically in most common cases, but can be overwritten for the uncommon ones.

All the goodness available from ActiveRecord is documented here.

It should be noted that there are some conventions it assumes:

• an Active Record class maps to a database table.
• database table names, like variable names, have lowercase letters and underscores between the words.
• table names are always plural.

If you want table names to be singular instead of plural, you can set the configuration parameter pluralize_table_names:

  ActiveRecord::Base.pluralize_table_names = false

Update:

Rails now (> V5) has a handy module we can include: include ActiveModel::Model This allows to initialise with a hash, and use validations amongst other things.

Full documentation is here.