Changes string_of_length to handle arrays

[LukasBarry]

Changes string_of_length to handle arrays

I recently discovered an error on a valid use case of the validates_length_of in the shoulda-matchers gem. I was attempting to test the length of an associated array, but kept receiving the same error:

NoMethodError:
       undefined method `each' for "":String

Here is the issue I submitted to Thoughtbot

Here is my suggested fix. I am new to contributing, so any feedback would be greatly appreciated!

[mcmire]

Hey @LukasBarry, thanks so much for the fix. I had a couple of comments below. Also, it doesn't look like there are any tests for this new behavior. Do you mind adding those? Thank you!

[mcmire]

Hmm... I'm not sure that this actually works like you think. I believe that @attribute here refers to the name of the attribute, not an attribute as a whole.

In order to properly check this, you have to look at the column type. Unfortunately, you can't make the assumption that the model being tested is an ActiveRecord model -- it could be an ActiveModel model, in which case there is no column and hence no type.

There are other matchers in which we do this properly; take a look at

shoulda-matchers/lib/shoulda/matchers/active_model/validate_inclusion_of_matcher.rb

Line 517 in ac9f482

def attribute_type

for inspiration. (Although it shouldn't be that complicated in this case -- you don't need to map :integer, for instance, to :fixnum or anything like that.)

[matsales28]

The idea behind this PR was resolved on #1560. I appreciate your contribution and time @LukasBarry. I'll be closing this PR. Maintainers, feel free to re-open the PR if you think otherwise.