On Sun, Jul 15, 2012 at 07:01:38AM -0700, Peter Brown wrote: > Is there an approved way to add or register a new ARel visitor without > adding it to the ARel source? Looking at the some of the source > code<https://github.com/rails/arel/blob/master/lib/arel/visitors/to_sql.rb#L434-466> > it > appears that new visitors are just hard coded as a new methods or aliases. > > The reason I'm asking is because I get "TypeError: Cannot visit ClassName" > when I override reader methods with some sort of composed object (similar > to Active Record's composed_of) and use that attribute in a uniqueness > validation. > > Take the following for example: > > class Cat < ActiveRecord::Base > validates :name, :uniqueness => { :scope => [:breed] } > > def breed > CatBreed.new(super) > end > end > > class CatBreed > def initialize(breed) > @breed = breed > end > > def to_s > @breed > end > end > > The above code will raise "TypeError: Cannot visit CatBreed" when I try to > create a new cat unless I add a visitor method to Arel::Visitors::ToSql > called visit_CatBreed: > > class Arel::Visitors::ToSql > def visit_CatBreed(value) > quoted(value.to_s) > end > end
Doing this is fine for now. The way the AST is translated to SQL won't change, so this will probably not break in the future. > I'm hoping there is a better way to deal with this problem, either with a > less hacky ARel approach or something different all together. It seems like we should be using the underlying database value (the attribute value rather than the return value of the method call) for the unique constraint. I think this might be a bug. Jon, wdyt? -- Aaron Patterson http://tenderlovemaking.com/
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