# How to connect to and use ActiveRecord outside of Rails?

Let's say you have a Ruby script and you would like to use `ActiveRecord` library inside it. Is it possible without Rails? Is it hard? It's possible and not hard at all.

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## Using ActiveRecord

Make sure your pure Ruby script starts by requiring `active_record`:

```ruby
require 'active_record'
```

## Connecting to database

### Connection defaults

I like to use [connection strings](/database-url-examples-for-rails-db-connection-strings/) instead of YAML/Hash with separate key-values to describe the connection.

```ruby
ENV['DATABASE_URL'] ||= "postgres://localhost/my_db_name?pool=5"
```

I prefer to use environment variables to set them because if I want to run the script on a different database, I can change it easily by setting an environment variable outside of the script. So this works nicely for me.

### Connect to database using the connection string

```ruby
ActiveRecord::Base.establish_connection(ENV['DATABASE_URL'])
```

That's it. This one-liner does the job.

## Models

You can now normally use the models in your script.

```ruby
class Event < ActiveRecord::Base
end
```

There is no `ApplicationRecord` so you can't inherit from it (unless you define that as well, yourself).

## Migrations

If the database does not already have the tables you are planning on using, you can create them with Active Record migrations. If you always want to have a clean state when you run the script, pass `force: true` to drop a table before creating it.

```ruby
ActiveRecord::Schema.define do
  self.verbose = true # or false

  enable_extension "plpgsql"
  enable_extension "pgcrypto"

  create_table(:events, force: true) do |t|
    t.string      :title,       null: false
    t.text        :description, null: false
    t.datetime    :created_at,  null: false
  end
end
```

Set `verbose` to `false` if you don't want to see the output of SQL statements creating those tables.

## Logger

If you want to see the SQL queries and commands executed by your script, don't forget to set a logger.

```ruby
require 'logger'
ActiveRecord::Base.logger = Logger.new(STDOUT)
```

Use `STDOUT` instead of a file, to output directly on the screen.

## Running the script

```bash
ruby my_script.rb
```

If you want to use different DB than the default:

```bash
DATABASE_URL=mysql2://root:@127.0.0.1/db_name?pool=5 ruby my_script.rb
```

If you want to always use specific `activerecord` version you need to create the `Gemfile`

```ruby
source 'https://rubygems.org'
gemspec
gem 'activerecord', '~> 5.1.3'
```

and run `bundle install`.

Execute the script with bundler:

```bash
bundle exec ruby my_script.rb
```

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