HasConfig

When working with models in a large Rails project, you sometimes end up with "god objects" which start to be loaded down with several booleans, integers, and strings from select boxes that act as configuration options. As time goes on, you add more and more columns. As your database and user-base grows, adding even a single column more can bring your app to a hang during a deploy due to table locking or a slew of exceptions due to issues and gotchas like this.

In an attempt to cut down on cluttering your model with boolean columns, has_config allows you to have a single column contain all configuration switches you could ever want. Adding another configuration option to a model no longer requires a migration to add a column. You can also continue writing code as if the model had all of those individual attributes.

Supported Rubies: 3.0 and later

Supported versions of ActiveRecord: 6.1 - 7.1

Add this line to your application's Gemfile:

gem 'has_config'

And then execute:

$ bundle

Or install it yourself as:

$ gem install has_config

Let's say we have a model called Client whose job is to hold the general information configuration for a client in a multi-tenant application. First, we need to add one column to the model to hold the configuration information. By default, the gem assumes the column's name is configuration, but you can change that (more on that later).

class AddConfigurationToClients < ActiveRecord::Migration
  add_column :clients, :configuration, :text
end

We now want to make that column a serialized hash in our model and include the HasConfig::ActiveReocrd::ModelAdapter module.

class Client < ActiveRecord::Base
  serialize :configuration, Hash
  include HasConfig::ActiveRecord::ModelAdapter
end

If you are using PostgreSQL 9.2 or later, you can use the JSON or JSONB (if using Rails 4.2 or later) data-type for the configuration column and not have to declare it as a serilaized attribute in the model as ActiveRecord will take care of that for you.

If you want to use a different column name, you may override the default by setting self.has_config_configuration_column = 'other_column_name' in the model.

class Client < ActiveRecord::Base
  serialize :configuration, Hash
  include HasConfig::ActiveRecord::ModelAdapter
  has_config :primary_color, config: { type: :string, default: 'green' }
  has_config :secondary_color, config: { type: :string }
  has_config :rate_limit, config: { type: :integer, validations: { numericality: { only_integer: true } } }
  has_config :category, config: { type: :string, validations: { inclusion: { in: CATEGORIES } } }
  has_config :active, config: { type: :boolean, default: false }
end

The has_config method is the primary interface for adding a setting to a model. The first argument is a symbol that represents the name of the setting.

The config key is a hash that contains information describing your setting. The type is the only required key when including the config option.

type is the datatype of your setting. Valid options are string, integer, and boolean.

default is the value that will be used if the record does not have this setting set. If no default is provided, nil will be used.

validations allows the setting to use the standard ActiveRecord validations you'd use for any regular attribute.

Ok, still with me? Back to our example...

Here, the Client model has five configuration items on it: primary_color, secondary_color, rate_limit, category, and active. So, knowing what you just learned above...

primary_color is a string with a default value of "green".

secondary_color is a string without a default.

rate_limit is an integer that validates its value is in fact, an integer.

category is a string that must be a value in the array CATEGORIES.

active is a boolean value with a default of false.

We can now access these configuration settings as if they were regular attributes on the model:

client = Client.new
client.default_color
=> "green"
client.secondary_color
=> nil
client.active
=> false
client.active?
=> false
client.active = '1' # Like if this was submitted from a form
=> '1'
client.active?
=> true
client.rate_limit = 3
=> 3
client.valid?
=> false
client.errors.full_messages
=> ["Category is not in the list"]

Everything acts pretty much as you'd expect it too do. Configurations that fail validations make the record invalid. Passing in '1', 'true', true, etc casts boolean values. Passing in an empty string for an integer config casts as nil.

Let's say you have a Client model, a Group model, and a User model. A client has many groups and a group can have many users. A client can have configuration which globally affects all users; however, a group setting of the same name could override the global setting. HasConfig can handle this with relative ease.

First, let's set up the models

class Client < ActiveRecord::Base
  has_many :groups
  # ...
  has_config :some_setting, config: { type: :integer, default: 3 }
end


class Group < ActiveRecord::Base
  belongs_to :client
  has_many :users

  # ...
  has_config :some_setting, config: { type: :integer }, parent: :client
end

This introduces a new option for the has_config method: parent. The parent option specifies a method HasConfig can use to defer the setting value to another object.

Assume we have a client and a group stored in our database:

g = Group.first
=> #<Group ...>
g.client
=> <#Client ...>
g.some_setting
=> nil
g.some_setting(:resolve)
=> 3
g.some_setting = 1
=> 1
g.some_setting(:resolve)
=> 1
g.some_setting = nil
=> nil
g.some_setting(:resolve)
=> 3

See what happened? Note the subtle change in how we reference the stting?

When we pass the symbol :resolve into the setting's getter method, and is blank, we will defer to the setting in the parent (in this case, Client) and use that value. If you do not pass :resolve in the getter, the local value will be used.

By default, HasConfig will go up the chain if the child model's value is blank (from ActiveSupport's blank? method).

You can chain as deep as you want as long as the object returned from parent includes a setting of the same name as the child. Meaning, your User model can chain some_setting up to group which can chain up to client.

You do have some control over when HasConfig invokes the change via the chain_on option for the setting's config:

# Chain will be invoked if the local value is `nil`
has_config :setting1, config: { type: :string, chain_on: :nil }, parent: :some_method

# Chain will be invoked if the local value is `false`
has_config :setting2, config: { type: :string, chain_on: :false }, parent: :some_other_method

An alternative to defining the definition of each setting in your model is to put them in a centralized configuration file.

Giving a file located at #{Rails.root}/config/has_config.rb:

has_config :primary_color, config: { type: :string, default: 'green' }
has_config :secondary_color, config: { type: :string }
has_config :rate_limit, config: { type: :integer, validations: { numericality: { only_integer: true } } }
has_config :category, config: { :string, validations: { inclusion: { in: CATEGORIES } } }
has_config :active, config: { type: :boolean, default: false }

... and then somewhere in your app, call HasConfig::Engine.load (There's an optional path: argument to specify a different file path)

This will load up pre-configured setting information in your app. You can then just refer to each setting by name in your model:

class Client < ActiveRecord::Base
  serialize :configuration, Hash
  include HasConfig::ActiveRecord::ModelAdapter
  has_config :primary_color
  has_config :secondary_color
  has_config :rate_limit
  has_config :category
  has_config :active
end

You can also override the default and validations options for a pre-defined config:

has_config :primary_color, config: { default: 'custom_value_unique_to_this_model' }

After checking out the repo, run bin/setup to install dependencies. Then, run rake to run the tests. You can also run bin/console for an interactive prompt that will allow you to experiment.

To install this gem onto your local machine, run bundle exec rake install. To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version, push git commits and tags, and push the .gem file to rubygems.org.

Bug reports and pull requests are welcome on GitHub at https://github.com/t27duck/has_config.

The gem is available as open source under the terms of the MIT License.