Sorry, I should've been more specific in my initial post:

   - I'm proposing this change *only* for has_one_attachment i.e. the 
   ability to use user.update! image: "" in place of user.image.detach
   - When comparing the behavior to has_many_attached, I mean in the sense 
   that has_many_attached detaches attachments when assigned a blank value (
   nil or []), i.e. user.update! highlights: nil

What would we do in the following cases? Ignore the empty strings? 


> user.update! highlights: [ "" ]
> user.update! highlights: [ "eyJfcmF--e31aef3", "" ]


You're right — in these cases it's not clear what should happen.

Currently the empty strings would raise the InvalidSignature error. I 
suppose it would behave like this, if blank strings were treated as 
"detachments" / discarded?

   - user.update! highlights: [ "" ] would effectively detach all highlights
   - user.update! highlights: [ "eyJfcmF--e31aef3", "" ] would attach a 
   single blob in the collection, i.e. user.highlights.length == 1
   

Kyle.

On Sunday, July 15, 2018 at 10:10:37 PM UTC-6, geo...@basecamp.com wrote:
>
> To be clear, the writer method added by has_many_attached does not 
> already accept empty strings.
>
> What would we do in the following cases? Ignore the empty strings?
>
> user.update! highlights: [ "" ]
> user.update! highlights: [ "eyJfcmF--e31aef3", "" ]
>
> George
>
> On Sunday, July 15, 2018 at 11:41:05 PM UTC-4, Kyle Fox wrote:
>>
>> ActiveStorage allows attachments to be attached by assigning a string 
>> representing a blob's signed_id. This works _brilliantly_ because it 
>> enables the same params conventions used when assigning other attributes 
>> through forms → controllers → models:
>>
>> params = { user: { image: 'eyJfcmF--e31aef3' } }
>>
>> However, it's surprising that setting the attachment to an empty string 
>> does _not_ detach the attachment:
>>
>> params = { user: { image: '' } } # => InvalidSignature
>>
>> It feels more Railsy to treat the empty string as a special case that 
>> detaches the attachment.
>>
>> This would allow attachments to be removed in a way that mirrors how they 
>> are added (i.e. posting hidden field values) instead of having to call 
>> @user.image.detach in a controller. For example, this would handle both 
>> attaching and detaching @user.image:
>>
>> @user.update_attributes(params.require(:user).permit(:name, :email, 
>> :image))
>>
>> Ideally in this scenario, if params[:user][:image] was '' ActiveStorage 
>> would call @user.image.detach.
>>
>> Currently if you assign an empty string to an attachment an 
>> ActiveSupport::MessageVerifier::InvalidSignature error is raised.
>>
>> Apparently 
>> <https://github.com/rails/rails/issues/33362#issuecomment-405080017> 
>> this is already how has_many_attached behaves — it'd be nice if 
>> has_one_attached behaved similarly.
>>
>> Any interest in this functionality? If so I'd be happy to put together a 
>> patch. 👍
>>
>

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