Upload text file without a dedicated model using active storage - ruby-on-rails

Question

I have a Task resource containing many tasks. I want to upload a text file containing multiple tasks and import them into the Task model.
I haven't used active storage (AS) before, so I have been combing through the docs. I get that the standard way of using AS is to have a model of records where each record has a file attached. I my case that would mean that I could create an importer model and the have one record for each import action. I feel that that is the wrong approach - I would much rather have an action on the task controller called import that can handle an uploaded file and the import all entries from the file into the task model.
I am trying to make this work with Direct Uploads I have created a form for this:
<%= form_with(model: #task, action: 'start_upload', local: true) do |form| %>
<%= form.file_field :attachments, multiple: false, direct_upload: true %>
<div class="form-group col-sm-6">
<%= form.submit "Save", :class => "btn btn-primary" %>
</div>
<% end %>
This works in some way; the file is uploaded - I see it in a folder (/Users/mhe/Documents/projects/mags/storage/3c/jf/3cjfvr062yd3y6wx8lly4llpdn9x). But I have no way of getting to the file.
The output to the log is:
Started POST "/rails/active_storage/direct_uploads" for ::1 at 2020-04-15 22:18:04 +0200
Processing by ActiveStorage::DirectUploadsController#create as JSON
Parameters: {"blob"=>{"filename"=>"movielist.txt", "content_type"=>"text/plain", "byte_size"=>23610, "checksum"=>"EEzCXGDVCwhcAzfHLvERaw=="}, "direct_upload"=>{"blob"=>{"filename"=>"movielist.txt", "content_type"=>"text/plain", "byte_size"=>23610, "checksum"=>"EEzCXGDVCwhcAzfHLvERaw=="}}}
(0.1ms) begin transaction
ActiveStorage::Blob Create (0.4ms) INSERT INTO "active_storage_blobs" ("key", "filename", "content_type", "byte_size", "checksum", "created_at") VALUES (?, ?, ?, ?, ?, ?) [["key", "ge8ztddg14tapio9cw0x7lf5lu79"], ["filename", "movielist.txt"], ["content_type", "text/plain"], ["byte_size", 23610], ["checksum", "EEzCXGDVCwhcAzfHLvERaw=="], ["created_at", "2020-04-15 20:18:04.108179"]]
(0.8ms) commit transaction
Disk Storage (0.3ms) Generated URL for file at key: ge8ztddg14tapio9cw0x7lf5lu79 (http://localhost:3000/rails/active_storage/disk/eyJfcmFpbHMiOnsibWVzc2FnZSI6IkJBaDdDVG9JYTJWNVNTSWhaMlU0ZW5Sa1pHY3hOSFJoY0dsdk9XTjNNSGczYkdZMWJIVTNPUVk2QmtWVU9oRmpiMjUwWlc1MFgzUjVjR1ZKSWc5MFpYaDBMM0JzWVdsdUJqc0dWRG9UWTI5dWRHVnVkRjlzWlc1bmRHaHBBanBjT2cxamFHVmphM04xYlVraUhVVkZla05ZUjBSV1EzZG9ZMEY2WmtoTWRrVlNZWGM5UFFZN0JsUT0iLCJleHAiOiIyMDIwLTA0LTE1VDIwOjIzOjA0LjExM1oiLCJwdXIiOiJibG9iX3Rva2VuIn19--f5314cff4278fed290a6ac3c1ee54c31542e9984)
Completed 200 OK in 19ms (Views: 0.3ms | ActiveRecord: 1.8ms | Allocations: 12779)
Started PUT "/rails/active_storage/disk/eyJfcmFpbHMiOnsibWVzc2FnZSI6IkJBaDdDVG9JYTJWNVNTSWhaMlU0ZW5Sa1pHY3hOSFJoY0dsdk9XTjNNSGczYkdZMWJIVTNPUVk2QmtWVU9oRmpiMjUwWlc1MFgzUjVjR1ZKSWc5MFpYaDBMM0JzWVdsdUJqc0dWRG9UWTI5dWRHVnVkRjlzWlc1bmRHaHBBanBjT2cxamFHVmphM04xYlVraUhVVkZla05ZUjBSV1EzZG9ZMEY2WmtoTWRrVlNZWGM5UFFZN0JsUT0iLCJleHAiOiIyMDIwLTA0LTE1VDIwOjIzOjA0LjExM1oiLCJwdXIiOiJibG9iX3Rva2VuIn19--f5314cff4278fed290a6ac3c1ee54c31542e9984" for ::1 at 2020-04-15 22:18:04 +0200
Processing by ActiveStorage::DiskController#update as */*
Parameters: {"encoded_token"=>"eyJfcmFpbHMiOnsibWVzc2FnZSI6IkJBaDdDVG9JYTJWNVNTSWhaMlU0ZW5Sa1pHY3hOSFJoY0dsdk9XTjNNSGczYkdZMWJIVTNPUVk2QmtWVU9oRmpiMjUwWlc1MFgzUjVjR1ZKSWc5MFpYaDBMM0JzWVdsdUJqc0dWRG9UWTI5dWRHVnVkRjlzWlc1bmRHaHBBanBjT2cxamFHVmphM04xYlVraUhVVkZla05ZUjBSV1EzZG9ZMEY2WmtoTWRrVlNZWGM5UFFZN0JsUT0iLCJleHAiOiIyMDIwLTA0LTE1VDIwOjIzOjA0LjExM1oiLCJwdXIiOiJibG9iX3Rva2VuIn19--f5314cff4278fed290a6ac3c1ee54c31542e9984"}
Disk Storage (4.7ms) Uploaded file to key: ge8ztddg14tapio9cw0x7lf5lu79 (checksum: EEzCXGDVCwhcAzfHLvERaw==)
No template found for ActiveStorage::DiskController#update, rendering head :no_content
Completed 204 No Content in 6ms (ActiveRecord: 0.0ms | Allocations: 5806)
Started POST "/tasks/upload" for ::1 at 2020-04-15 22:18:04 +0200
Processing by TasksController#do_upload as HTML
Parameters: {"authenticity_token"=>"wufWKGXHYX/obGYtKkL8SVSy5uSd/Z2XFLDxvLkDKdGQicsUPjEks9riYloTzorjhX8PgFUIj/BXV4VFi1ihKQ==", "attachments"=>"eyJfcmFpbHMiOnsibWVzc2FnZSI6IkJBaHBEZz09IiwiZXhwIjpudWxsLCJwdXIiOiJibG9iX2lkIn19--c47b93b4598d01bf7f9b47caa0660fd39ab9b8df", "commit"=>"Save"}
Completed 500 Internal Server Error in 2ms (ActiveRecord: 0.0ms | Allocations: 1300)
And thus the params I get from the upload form are simply:
{"authenticity_token"=>"wufWKGXHYX/obGYtKkL8SVSy5uSd/Z2XFLDxvLkDKdGQicsUPjEks9riYloTzorjhX8PgFUIj/BXV4VFi1ihKQ==", "attachments"=>"eyJfcmFpbHMiOnsibWVzc2FnZSI6IkJBaHBEZz09IiwiZXhwIjpudWxsLCJwdXIiOiJibG9iX2lkIn19--c47b93b4598d01bf7f9b47caa0660fd39ab9b8df", "commit"=>"Save", "controller"=>"tasks", "action"=>"do_upload"}
I read about how I should be able to do something like this:
blob = ActiveStorage::Blob.create_after_upload!(
io: params[:file],
filename: params[:file].original_filename,
content_type: params[:file].content_type
)
render json: { filelink: url_for(blob) }
or
ActiveStorage::Blob.service.path_for(params['key'])
But I don't have file nor key in the params - I see them output to the log, though.
So I'm looking for some guidance on how to achieve the usecase... thanks