No one wants to manage data without an admin panel

No developer wants to manage application data without the benefit of a front-end interface, and APIs are no exception.

Rails 5 makes it easy to build a beautiful and clean API, but when data starts flowing you need an easy way to visualize and manage it.

Rails has admin frameworks, but they don’t work for API apps

The good news is there are already plenty of great admin panel solutions, the most popular being Active Admin.

But here’s the problem: you can’t use it with Rails 5 API application…

Because API-mode omits all the middleware for rendering HTML, installing Active Admin will fail when it tries to generate views and assets for its dashboard.

You have a hard choice to make…

Should you abandon API-only mode in favor of the full Rails stack?

You obviously don’t want to lose all the benefits of the slimmed-down middleware stack for your API controllers. So having to set config.api_mode = false feels like a failure.

What about creating an entirely new and separate Rails app just for Active Admin?

Maintaining separate repositories and deployments, as well as trying to share business logic across apps is a lot more work and adds maintenance overhead.

Why not the best of both worlds?

Here’s how to get Active Admin (AA) working on a Rails 5 API-only application, without having to disable API mode altogether or create separate apps.

1. Inherit from ActionController::Base

Running the AA install generator results in the following error

undefined method `helper_method' for InheritedResources::Base:Class (NoMethodError)

To fix, view rendering needs to be re-enabled for the AA base controller which inherits from ApplicationController.

NOTE: This inheritance relationship is an unfortunate design choice that has been brought up a couple times before. It would be better to create an admin-specific base controller and namespace instead of having to make such a global change to ApplicationController, but this isn’t possible with Active Admin as its currently coded.

But first, in order to keep all the API-mode goodness for controllers handling API requests, you’re going to want to create a new controller base class that inherits from ActionController::API. Move any application code that applies to API requests there.

class ApiController < ActionController::API
  # move API-specific filters/logic from ApplicationController to here

Update all your API controllers to inherit from this new base class.

Now change the ApplicationController to inherit from ActionController::Base.

class ApplicationController < ActionController::API
# change to =>
class ApplicationController < ActionController::Base

This will allow the install generator to successfully run.

2. Enable the flash

The install generator runs, but your dashboard is not viewable yet.

ActionView::Template::Error: undefined method `flash'

You need to add in the middleware which enables the flash.

# config/application.rb
module MyApp
  class Application < Rails::Application
    # ...

    # add this =>
    config.middleware.use ActionDispatch::Flash

You now have a working dashboard!

3. (For Devise) Allow session management

You are most likely using Devise for authentication on your admin panel.

At this point, sign in attempts will fail and keep redirecting back to the sign in page, even though your credentials are correct.

To sign in successfully, you need to enable the middleware for session management.

# config/application.rb
module MyApp
  class Application < Rails::Application
    # ...

    # add these =>
    config.middleware.use ActionDispatch::Cookies
    config.middleware.use ActionDispatch::Session::CookieStore

Congratulations, you can now successfully sign in and access your Active Admin dashboard!

Your setup may require more config

The steps above are for a basic Rails 5 API application with no other gems or frameworks added.

Your own app may include dependencies which rely on additional middleware or other configuration to get Active Admin working. If so, post in the comments below.

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