Rails Modeler

Generate Mermaid ER diagrams from your Rails model associations and schema.

Unlike schema-only tools, Rails Modeler reads has_many, has_one, belongs_to, and has_and_belongs_to_many declarations via Rails' Reflection API, and extracts attributes from db/schema.rb.

Installation

Add to your Gemfile:

gem "rails_modeler", group: :development

Then run:

bundle install

Usage

Generate the diagram:

rake rails_modeler:generate

This writes a .mmd file (default: docs/schema.mmd) and prints the diagram to stdout.

Configuration

Create an initializer at config/initializers/rails_modeler.rb:

RailsModeler.configure do |config|
  config.excluded_models = ["ActiveStorage::Blob", "ActiveStorage::Attachment"]
  config.output_path = "docs/er_diagram.mmd"
  config.show_attributes = true
  config.title = "My App Schema"
end

Option	Default	Description
excluded_models	[]	Model names to omit from the diagram
output_path	"docs/schema.mmd"	Where to write the .mmd file
show_attributes	true	Include column attributes in entity blocks
title	"Schema"	Diagram title

Example Output

erDiagram
    Author {
        integer id PK
        string name
    }
    Article {
        integer id PK
        string title
        integer author_id FK
    }
    Author ||--o{ Article : "has_many"

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Supported Associations

• belongs_to (including polymorphic)
• has_many (including as: polymorphic)
• has_one
• has_and_belongs_to_many

Bidirectional associations are automatically deduplicated.

Development

bundle install
bundle exec rspec

License

MIT License. See LICENSE.txt.