How to make has_attached_file dynamic depending on form values

[Christian Fazzini]

My form submits with a column called stream_type, which can either be
"full", "30secs" or "90secs".

How can i set it so that it sets has_attached_file according to the
form value stream_type?

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Model class looks like this:

has_attached_file :media,
:styles => { :original =>
<need_to_set_dynamic_content_here> },
:url => '/assets/artists/:artist_id/
songs/:id/:style.:extension',
:path => ':rails_root/public/assets/
artists/:artist_id/songs/:id/:style.:extension',
:processors => [:process_audio]

--------------

So for example, if my form submits with stream_type = 90secs, then
has_attached_file will look like:

has_attached_file :media,
:styles => { :original => '30' },
:url => '/assets/artists/:artist_id/
songs/:id/:style.:extension',
:path => ':rails_root/public/assets/
artists/:artist_id/songs/:id/:style.:extension',
:processors => [:process_audio]