Clear ActiveStorage::Blob column information in migration file

[ohbarye]

This is just a proposal for an improvement. If you feel it's meaningless, I'm okay to withdraw.

Summary

This pull request attempts to eliminate a possible problem that could happen when calling ActiveStorage::Blobs in future migrations.

As documented in https://api.rubyonrails.org/classes/ActiveRecord/ModelSchema/ClassMethods.html#method-i-reset_column_information, we can avoid the problem by calling reset_column_information before calling the model in the next migration script.

However, I think it's a better practice to call reset_column_information after touching a model in advance in order to eliminate a future problem rather than postponing the problem in the future.

Other Information

Nothing.

[georgeclaghorn]

What specifically is this fixing? Do you have a concrete example you can share of something that doesn’t work without this change?

[ohbarye]

Okay, let me show what I imagined.

If I would have another migration script that adds a new column to ActiveStorage::Blob and populates default values as like activestorage/db/update_migrate/20190112182829_add_service_name_to_active_storage_blobs.rb does. (I know it's unlikely that a Rails user adds a column to the table, it's more likely that Rails core adds a column to provide a new feature.)

# db/migrate/xxxx_add_new_column_to_active_storage_blobs.rb
class AddNewColumnToActiveStorageBlobs < ActiveRecord::Migration
  def up
    add_column :active_storage_blobs, :new_column, :string
    ActiveStorage::Blob.update_all(new_column: "some default value")
  end
end

When running activestorage/db/update_migrate/20190112182829_add_service_name_to_active_storage_blobs.rb and the migration above at the same time,.update_all raises the following error unless calling .reset_column_information before .update_all. That's because ActiveStorage::Blob has cached column information since activestorage/db/update_migrate/20190112182829_add_service_name_to_active_storage_blobs.rb

ActiveModel::UnknownAttributeError: unknown attribute 'new_column' for ActiveStorage::Blob.

---

There's nothing that doesn’t work without this change as of now. So I think it's rather prevention than fix.

[rails-bot]

This pull request has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs.
Thank you for your contributions.

[zzak]

Doesn't this have potentially surprising effects if the user does not expect their column information to be reset 🤔

[rails-bot]

This pull request has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs.
Thank you for your contributions.