The Hidden DSL Inside Every Rails Model

June 10, 2026

Most Rails developers use belongs_to, has_many, scope, and validates every day.

We type them almost without thinking.

class User < ApplicationRecord
  belongs_to :company

  validates :email, presence: true

  scope :active, -> { where(active: true) }
end

But here’s something interesting:

None of those are Ruby keywords.

They’re methods.

In fact, a Rails model is less like a traditional Ruby class and more like a Domain Specific Language (DSL) built on top of Ruby.

Once you see it, it’s hard to unsee.

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The Empty Model

A Rails model starts life as a completely ordinary Ruby class.

class User < ApplicationRecord
end

At first glance, there’s nothing special here.

User inherits from ApplicationRecord, which inherits from ActiveRecord::Base.

That’s where the magic begins.

By inheriting from Active Record, the class gains hundreds of methods that allow us to describe data, relationships, validations, callbacks, and behavior using a concise DSL.

Associations

Consider this:

class User < ApplicationRecord
  belongs_to :company

  has_many :posts
end

When Rails reads these lines, it isn’t creating relationships in the database.

It’s executing methods.

Those methods generate additional behavior behind the scenes.

After declaring belongs_to :company, Rails creates methods such as:

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The Hidden DSL Inside Every Rails Model June 10, 2026 Most Rails developers use belongs_to, has_many, scope, and validates every day. We type them almost without thinking. class User < Applicati…

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