Uniqueness validator returns exists for non existing records about mobility

[jonian]

It seems that the problem is in mobility/lib/mobility/active_record/uniqueness_validator.rb line 14.

if relation.exists?
  error_options = options.except(:case_sensitive, :scope, :conditions)
  error_options[:value] = value

  record.errors.add(attribute, :taken, error_options)
end

Using relation.exists? or relation.any? I get the same error. If i use relation.present?, it works as expected.

[shioyama]

Ok I found the root cause.

For the record, it's this line, which checks if the relation responds to a method (mobility_where_chain). Calling respond_to?, which should be fine, actually memoizes an arel object here in AR. This in turn is picked up by assert_mutability! here, which is what's raising the error.

I can fix this by replacing relation.respond_to? by relation.methods.include?, which seems ugly but works. This feels like an AR bug but I don't know the internals of what must have changed, so not quite sure...

Anyway that change should be relatively harmless and fix the issue in Rails 5.1. 😄

[shioyama]

This should be fixed now on master, please give it a try.

[jonian]

@shioyama I confirm that this is working without issues now. Thank you for the quick fix.