Simulating selecting a file for Active Storage in irb - ruby-on-rails

Question

Creating a new item for Active Storage.
<!-- app/views/docs/_form.html.erb -->
<%= f.label :image, "Select document or image that support this information." %>
<%= f.file_field :image %>
I'm getting a Please review the problems below error when I click Create and thought I'd see what errors happen in irb. But how do I simulate the above step.
Models:
# models/doc.rb
class Doc < ApplicationRecord
has_one_attached :image # Active Storage
belongs_to :source
belongs_to :docable, polymorphic: true
# models/source.rb
class Source < ApplicationRecord
has_many :docs
# models/year.rb
class Year < ApplicationRecord
belongs_to :location
belongs_to :person
has_many :docs, as: :docable
# models/person.rb
class Person < ApplicationRecord
has_many :years, dependent: :destroy
has_many :locations, through: :years
has_many :docs, as: :docable
# models/location.rb
class Location < ApplicationRecord
has_many :years
has_many :people, through: :years
has_many :docs, as: :docable
Where a person lived or worked at on a date is set in years. year, person and location use doc to show the reference for that information.
The source is the title of an old book and I'm imaging various pages in the book. Later I refer to those images using docable (that's the plan).
db/structure.sql: CREATE INDEX index_docs_on_docable_type_and_docable_id ON public.docs USING btree (docable_type, docable_id);
Here's the session:
irb(main):100:0> doc = Doc.new
=> #<Doc id: nil, source_id: nil, page_no: nil, original_url: nil, basename: nil, created_at: nil, updated_at: nil, notes: nil, docable_id: nil, docable_type: nil>
irb(main):101:0> doc.save
=> false
irb(main):102:0> doc.errors.messages
=> {:source=>["must exist"], :docable=>["must exist"]}
irb(main):104:0> doc.source_id = 4
=> 4
irb(main):105:0> doc.save
(42.8ms) BEGIN
Source Load (45.3ms) SELECT "sources".* FROM "sources" WHERE "sources"."id" = $1 LIMIT $2 [["id", 4], ["LIMIT", 1]]
(0.2ms) ROLLBACK
=> false
irb(main):106:0> doc.errors.messages
=> {:docable=>["must exist"]}
irb(main):107:0> doc.image =
I may have problems with the polymorphic relationship, so I'm trying to sort that out.

Answer 1

https://edgeguides.rubyonrails.org/active_storage_overview.html#attaching-file-io-objects
doc.image.attach(io: File.open('/path/to/file'), filename: 'file.jpg')