Question

I have an AR association with extensions in Rails similar to the example presented in this link:
ActiveRecord Association Extensions

has_many :issues, :through => :qbert_issues do
  def tracking
    where("qbert_issues.kind = ?", "tracking")
  end

  def blocking
    where("qbert_issues.kind = ?", "blocking")
  end
end

As shown above, mine is multi-typed… I need to populate a ‘kind’ column in my join table. Ideally, this should just work:

q = QBert.find(123)
q.issues.tracking << Issue.find(234)

So, what the article suggests is overloading << and doing something like this:

has_many :issues, ... do
  ...
  def <<(issue)
    issue.kind = "UserAccount"
    proxy_association.owner.issues += [issue]
  end
end

Which would be nice, if kind was static.

It looks like I can do this…

has_many :issues, ... do
  ...
  def <<(*args)
    issue, kind = args.flatten
    issue.kind = kind
    proxy_association.owner.issues += [issue]
  end
end

Which would allow me to do this at the very least:

q = QBert.find(123)
q.issues.tracking << [Issue.find(234), :tracking]

That doesn’t seem very DRY to me…is there a better way? Bonus points if you take into account that the kind accessor is off a join table qbert_issues. I’m guessing I just have to add the association manually through the QBertIssue model directly.

Answer 1

Figured it out…

def <<(issue)
  kind = where_values.second.scan(/kind = '(.*)'/).flatten.first
  left = proxy_association.reflection.source_reflection
  right = proxy_association.reflection.through_reflection

  left.active_record.create(left.foreign_key.to_sym => issue.id, 
                            right.foreign_key.to_sym => proxy_association.owner.id, 
                            :kind => kind)
end

Which lets me do:

q = QBert.find(123)
q.issues.tracking << Issue.find(234)

It could be made sufficiently generalized by parsing out the where_values and merging them into the parameters hash.

Pry rocks, by the way 😀