Active Storage Blob 可识别

# File activestorage/app/models/active_storage/blob/identifiable.rb, line 17
def identified?
  identified
end

# File activestorage/app/models/active_storage/blob/identifiable.rb, line 5
def identify
  identify_without_saving
  save!
end

# File activestorage/app/models/active_storage/blob/identifiable.rb, line 10
def identify_without_saving
  unless identified?
    self.content_type = identify_content_type
    self.identified = true
  end
end