Rails Mermaid ERD
Generate Mermaid ERD from your Ruby on Rails application.
Mermaid ERD can be generated at will. The generated ERD can be copied in Markdown format, so they can be easily shared on GitHub. You can also save it as an image, so it can be used in environments where Mermaid is not available. The editor is a single HTML file, so the entire editor can be shared.
Installation
Add this line to your application's Gemfile:
gem "rails-mermaid_erd", group: :development, require: false
And then execute:
$ bundle install
Add this line to your application's Rakefile:
begin
require "rails-mermaid_erd"
rescue LoadError
# Do nothing.
end
Usage
Run rake task mermaid_erd will generate <app_root>/mermaid_erd/index.html.
$ bundle exec rails mermaid_erd
# or
$ bundle exec rake mermaid_erd
Simply open the generated <app_root>/mermaid_erd/index.html in your browser.
This file is not required for Git management, so you can add it to .gitignore if necessary
mermaid_erd
<app_root>/mermaid_erd/index.html is a single self-contained HTML file. All front-end dependencies (Tailwind, Mermaid, Vue) are inlined, so it works offline and behind strict corporate proxies — no CDN access is needed at view time. The file is roughly 4 MB because the bundles ship inside it.
If you share this file, it can be used by those who do not have a Ruby on Rails environment. Or, you can upload the file to a web server and share it with the same URL.
It would be very smart to generate it automatically using CI.
Supported versions
The Ruby × Rails combinations exercised by CI on every push and pull request:
| Rails | Ruby |
|---|---|
| 5.2 | 2.7 |
| 6.0 | 2.7, 3.0 |
| 6.1 | 2.7, 3.0, 3.1, 3.2 |
| 7.0 | 2.7, 3.0, 3.1, 3.2, 3.3 |
| 7.1 | 3.1, 3.2, 3.3, 3.4 |
| 7.2 | 3.1, 3.2, 3.3, 3.4 |
| 8.0 | 3.2, 3.3, 3.4, 4.0 |
| 8.1 | 3.2, 3.3, 3.4, 4.0 |
Other combinations may work but are not verified.
Configuration
./config/mermaid_erd.yml to customize the configuration.
See ./docs/example.yml for an example configuration.
The setting items are as follows.
| key | description | default |
|---|---|---|
result_path |
Destination of generated files. | mermaid_erd/index.html |
ignore_tables |
Array of regular-expression strings. Tables whose table_name matches any pattern are dropped from the generated ERD, along with any relations that point at them. Useful for excluding audit-log models, soft-deleted/legacy tables, or other large noise you don't want to render. Patterns are compiled with Regexp.new, so escape backslashes inside YAML strings (e.g. "\\Aaudit_"). |
[] |
License
The gem is available as open source under the terms of the MIT License.