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Desiree Lerma
Desiree Lerma

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What I Learned This Week: Rails ActiveStorage

Recently, I completed a code challenge that included some bonus items. One of those bonus items involved image uploading which I had not yet done before. So, I decided to make it my goal this week to learn how to implement ActiveStorage to allow image and document uploading into an application. ActiveStorage eliminates the need for external gems to allow for image and document uploading. ActiveStorage also supports the use for different Cloud based storage systems such as Amazon S3, Microsoft Azure, Google Cloud Storage or you may use your computer's local disk.

First, after you've created or opened your app, install ActiveStorage with the command rails active_storage:install.
This line will do exactly what it says... install ActiveStorage. Using this command will also create ActiveStorage tables that will then need to be migrated with rails db:migrate. Let's take a quick look at the tables that were created.

ActiveStorage Database Tables

Holy moly! That looks like a bunch of information, right?! Not to worry, these tables are essentially doing the following:

  • Storing filename, byte size, content type, etc.
  • Joining the attachment to the Model owner. (Think a User and their avatar)

If you are using Cloud storage you will also need to create a .env file and add that to a .gitignore file. This is extremely important so that your keys do not get used by others viewing your repository which can lead to charges on your Cloud storage account! This file will then contain the information needed to use the Cloud storage service.

# .env file
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In storage.yml ActiveStorage has configured the different Cloud options available. Simply uncomment whichever service you wish to use and reference your .env file.

storage.yml File

Next, go into development.rb and/or production.rb and update the line of code that references the ActiveStorage service to use whichever service you prefer. Otherwise, it will automatically default to your local storage.

config.active_storage.service = :local
config.active_storage.service = :amazon
config.active_storage.service = :google
config.active_storage.service = :azure
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Now that we've got the Cloud stuff out of the way we can move on to our Model relations. ActiveStorage gives us has_one_attached and has_many_attached which sets up mapping between records and files.

User Model with ActiveStorage Associations

Make sure, in the associated Controller, to allow the image/document to be permitted in the params. In my example, since there are many documents, I set documents to an empty array to allow it to take in multiple.

Permit Params

Finally, if you're using a frontend or views, add in a file_field to the associated form for the image/document to be uploaded. If you make use of has_many_attached, be sure to set multiple to true in the form. Don't forget about the show page! In the show page (or where ever the image/document is going to be displayed) be sure to call the proper association to have the image/document display.

Add File Field to View/Form

If/Else for User Show Page

Tada!! Now, ActiveStorage has been successfully added to your application. I hope this walk through helps even a tad.


  • ActiveStorage supports uploading directly from the client to the cloud. To do so, set direct_upload to true to begin upload on form submission.

  • Use variant to transform your image/document. With variant you can do things like resize or format. To use variant you will need to add the gem image_processing which relies on ImageMagick. ImageMagick will need to be installed on your operating system as it is not a Ruby gem.

  • attached? is also given to us from ActiveStorage. Basically, it checks if there is an attachment present or not.


Top comments (1)

mtnbiker profile image
Greg S

Credentials is recommended for storing passwords instead of the .env file. Search for rails credentials for other discussions. This topic is confusing but important.

Thank you for this overview.