How to validate a binary field using Ruby on Rails? - mysql

Question

I want to ensure that a binary field has always value. I added a validation code like below.
class Foo < ActiveRecord::Base
validates :b, presence: true
end
However, the change seems to cause the error.
$ rails c
> Foo.create(b:File.read('b.jpg'))
ArgumentError: invalid byte sequence in UTF-8
The error doesn't always appear. Only when the binary data has non-ascii codes.
How can I validate the binary field?
I made the environment like below. A image file(b.jpg, less than 16KB) is also needed.
$ rails --version
Rails 4.2.0
$ rails new test_binary --database=mysql
$ cd test_binary/
$ rails g model foo b:binary
$ rake db:create db:migrate

Answer 1

File.read returns a String that will claim to have UTF-8 encoding by default. That means that this:
Foo.create(b: File.read('b.jpg'))
is really:
some_utf8_string = File.read('b.jpg')
Foo.create(b: some_utf8_string)
But a JPEG will rarely be a valid UTF-8 string so you're going to get that ArgumentError whenever someone tries to treat it as UTF-8.
You can specify an encoding when you read your JPEG:
Foo.create(b: File.read('b.jpeg', encoding: 'binary'))
That should get past your encoding problem.