Code Generation with Super Scaffolding

Super Scaffolding is Bullet Train’s code generation engine. Its goal is to allow you to produce production-ready CRUD interfaces for your models while barely lifting a finger, and it handles a lot of other grunt-work as well.

Here’s a list of what Super Scaffolding takes care of for you each time you add a model to your application:

  • It generates a basic CRUD controller and accompanying views.
  • It generates a Yaml locale file for the views’ translatable strings.
  • It generates type-specific form fields for each attribute of the model.
  • It generates an API controller and an accompanying entry in the application’s API docs.
  • It generates a serializer that’s used by the API and when dispatching webhooks.
  • It adds the appropriate permissions for multitenancy in CanCanCan’s configuration file.
  • It adds the model’s table view to the show view of its parent.
  • It adds the model to the application’s navigation (if applicable).
  • It generates breadcrumbs for use in the application’s layout.
  • It generates the appropriate routes for the CRUD controllers and API endpoints.

When adding just one model, Super Scaffolding generates ~30 different files on your behalf.

Living Templates

Bullet Train's Super Scaffolding engine is a unique approach to code generation, based on template files that are functional code instead of obscure DSLs that are difficult to customize and maintain. Super Scaffolding automates the most repetitive and mundane aspects of building out your application's basic structure. Furthermore, it does this without leaning on the magic of libraries that force too high a level of abstraction. Instead, it generates standard Rails code that is both ready for prime time, but is also easy to customize and modify.


Before getting started with Super Scaffolding, we recommend reading about the philosophy of domain modeling in Bullet Train.


The Super Scaffolding shell script provides its own documentation. If you're curious about specific scaffolders or parameters, you can run the following in your shell:



1. Basic CRUD Scaffolding with crud

Let's implement the following feature:

An organization has many projects.

First, generate the model with the standard Rails generator:

rails g model Project team:references name:string

In the above example, team represents the model that a Project primarily belongs to.

⚠️ Don't run migrations right away. It would be fine in this case, but sometimes the subsequent Super Scaffolding step actually updates the migration as part of its magic.

Next, run the crud scaffolder:

bin/super-scaffold crud Project Team name:text_field
rake db:migrate

In the above example, text_field was selected from the list of available field partials. We'll show examples with trix_editor and super_select later.

2. Nested CRUD Scaffolding with crud

Building on that example, let's implement the following feature:

A project has many goals.

Again, we'll generate the model using the standard Rails generator:

rails g model Goal project:references description:string

You can see in the example above that there is no direct reference to team, but to project instead, since that's where a Goal belongs.

Now, run the crud scaffolder:

bin/super-scaffold crud Goal Project,Team description:text_field
rake db:migrate

You can see in the example above how we've specified Project,Team, because we want to specify the entire chain of ownership back to the Team. This allows Super Scaffolding to automatically generate the required permissions.

3. Adding New Fields with crud-field

One of Bullet Train's most valuable features is the ability to add new fields to existing scaffolded models. When you add new fields with the crud-field scaffolder, you don't have to remember to add that same attribute to table views, show views, translation files, API endpoints, serializers, tests, documentation, etc.

Building on the earlier example, consider the following new requirement:

In addition to a name, a project can have a description.

First, use the standard Rails migration generator to add the attribute in the database:

rails g migration add_description_to_projects description:text

Then, use the crud-field scaffolder to add it throughout the application:

bin/super-scaffold crud-field Project description:trix_editor
rake db:migrate

As you can see, when we're using crud-field, we don't need to supply the chain of ownership back to Team.

If you want to scaffold a new field to use for read-only purposes, add the following option to omit the field from the form and all other files that apply:

bin/super-scaffold crud-field Project description:trix_editor{readonly}

4. Adding Option Fields with Fixed, Translatable Options

Continuing with the earlier example, let's address the following new requirement:

Users can specify the current project status.

We have multiple field partials that we could use for this purpose, including buttons, options, or super_select.

In this example, let's add a status attribute and present it as buttons:

rails g migration add_status_to_projects status:string
bin/super-scaffold crud-field Project status:buttons

By default, Super Scaffolding configures the buttons as "One", "Two", and "Three", but in this example you can edit those options in the fields section of config/locales/en/projects.en.yml. For example, you could specify the following options:

planned: Planned
started: Started
completed: Completed

If you want new Project models to be set to planned by default, you can add that to the migration file that was generated before running it, like so:

add_column :projects, :status, :string, default: "planned"

5. Scaffolding belongs_to Associations, Team Member Assignments

Continuing with the example, consider the following requirement:

A project has one specific project lead.

Although you might think this calls for a reference to User, we've learned the hard way that it's typically much better to assign resources on a Team to a Membership on the team instead. For one, this allows you to assign resources to new team members that haven't accepted their invitation yet (and don't necessarily have a User record yet.)

We can accomplish this like so:

rails g migration add_lead_to_projects lead:references

Then, to add the field, we specify the following:

bin/super-scaffold crud-field Project lead_id:super_select{class_name=Membership}
rake db:migrate

There are two important things to point out here:

  1. When we use rails g model or rails g migration, we specify the references column name as lead, but when we're specifying the field we want to scaffold, we specify it as lead_id, because that's the name of the attribute on the form, in strong parameters, etc.
  2. We have to specify the model name with the class_name option so that Super Scaffolding can fully work it's magic. We can't reflect on the association, because at this point the association isn't properly defined yet. With this information, Super Scaffolding can handle that step for you.

Finally, Super Scaffolding will prompt you to edit app/models/project.rb and implement the required logic in the valid_leads method. This is a template method that will be used to both populate the select field on the Project form, but also enforce some important security concerns in this multi-tenant system. In this case, you can define it as:

def valid_leads

(The current_and_invited scope just filters out people that have already been removed from the team.)

6. Scaffolding Has-Many-Through Associations with join-model

Finally, working from the same example, imagine the following requirement:

A project can be labeled with one or more project-specific tags.

We can accomplish this with a new model, a new join model, and a super_select field.

First, let's create the tag model:

rails g model Projects::Tag team:references name:string
bin/super-scaffold crud Projects::Tag Team name:text_field

Note that project tags are specifically defined at the Team level. The same tag can be applied to multiple Project models.

Now, let's create a join model for the has-many-through association:

rails g model Projects::AppliedTag project:references tag:references

We're not going to scaffold this model with the typical crud scaffolder, but some preparation is needed before we can use it with the crud-field scaffolder, so we need to do the following:

bin/super-scaffold join-model Projects::AppliedTag project_id{class_name=Project} tag_id{class_name=Projects::Tag}

All we're doing here is specifying the name of the join model, and the two attributes and class names of the models it joins. Note again that we specify the _id suffix on both of the attributes.

Now that the join model has been prepared, we can use the crud-field scaffolder to create the multi-select field:

bin/super-scaffold crud-field Project tag_ids:super_select{class_name=Projects::Tag}
rake db:migrate

Just note that the suffix of the field is _ids plural, and this is an attribute provided by Rails to interact with the has_many :tags, through: :applied_tags association.

The crud-field step will ask you to define the logic for the valid_tags method in app/models/project.rb. You can define it like so:

def valid_tags

Honestly, it's crazy that we got to the point where we can handle this particular use case automatically. It seems simple, but there is so much going on to make this feature work.

7. Scaffolding image upload attributes

Bullet Train comes with two different ways to handle image uploads.

  • Cloudinary - This option allows your app deployment to be simpler because you don't need to ship any image manipulation libraries. But it does introduce a dependence on a 3rd party service.
  • ActiveStorage - This option doesn't include reliance on a 3rd party service, but you do have to include image manipulation libararies in your deployment process.

Scaffolding images with Cloudinary

When you scaffold your model you need to include a string where Cloudinary can store a reference to the image.

For instance to scaffold a Project model with a logo image upload.

rails g model Project team:references name:string logo:string

Then you can use image as a field type for super scaffolding:

bin/super-scaffold crud Project Team name:text_field logo:image
rake db:migrate

Scaffolding images with ActiveStorage

When you scaffold your model you need to generate an attachment type attribute.

For instance to scaffold a Project model with a logo image upload.

rails g model Project team:references name:string logo:attachment

Then you can use image as a field type for super scaffolding:

bin/super-scaffold crud Project Team name:text_field logo:image
rake db:migrate

Additional Notes

TangibleThing and CreativeConcept

In order to properly facilitate this type of code generation, Bullet Train includes two models in the Scaffolding namespace as a parent and child model:

  1. Scaffolding::AbsolutelyAbstract::CreativeConcept
  2. Scaffolding::CompletelyConcrete::TangibleThing

Their peculiar naming is what's required to ensure that their corresponding view and controller templates can serve as the basis for any combination of different model naming or namespacing that you may need to employ in your own application. There are a ton of different potential combinations of parent and child namespaces, and these two class names provide us with the fidelity we need when transforming the templates to represent any of these scenarios.

Only the files associated with Scaffolding::CompletelyConcrete::TangibleThing actually serve as scaffolding templates, so we also take advantage of Scaffolding::AbsolutelyAbstract::CreativeConcept to demonstrate other available Bullet Train features. For example, we use it to demonstrate how to implement resource-level collaborators.

Hiding Scaffolding Templates

You won't want your end users seeing the Super Scaffolding templates in your environment, so you can disable their presentation by setting HIDE_THINGS in your environment. For example, you can add the following to config/application.yml:


Advanced Examples