> It actually seems to get a little sticky for purging, below I am
> outlining how it works, I was just curious if anyone has spent time
> thinking about this use case before and how it should work:
>
> As far as I can tell, the title_patterns can only map in one direction
> title->parameters
That's correct. Since it's made up of two non-invertible operations
(matching a regular expression & mapping through lambdas) there's no
automatically generated inverse operation. We (Stephan and I) discussed
providing support for a converse operation (something like a micro-erb
template that would produce a title based on the other attributes) but
since we couldn't come up with compelling use case at the time we
decided it was out of scope.
> (more on why they may have to map the other way in a second :) ).
>
> When we call self.instances during purging, the following series of
> events occur (with parsed file)
>
> - generate each record
> - this is able to generate a record that includes the params
> that compose the composite namevar
> - this record (which is a hash) is then converted into a resource
> - when converted into a resources, it calls hash2resource, which
> picks a title if one has not been specified:
>
> 910 title = hash.delete(:title)
> 911 title ||= hash[:name]
> 912 title ||= hash[key_attributes.first] if
> key_attributes.length == 1
>
> - it is impossible for this code to generate a valid title for a
> composite title (since it doesn't know how to map backwards from the
> params out of the has to the composite title)
>
> now that we have a title that is invalid
You, on the other hand, have a pretty good one right there. :)
>
> - we call to_hash when we generate the original parameters
>
> @original_parameters = resource.to_hash
>
> - to_hash tries to parse the title (using def parse_title), which
> leads to failures b/c the title is invalid
>
> I can get around this by adding the following pattern:
>
> # this pattern is required for purging
> [ /^(.*)$/,
> [
> [ :name, lambda{|x| x} ]
> ]
> ]
>
> which is added just for purging
Hmmm. I'm not seeing how that actually fixes it rather than just hiding
it by setting the name to the title so it can later set the title to the
name. I think what's really needed is to have hash2resource be smarter
about assigning a title...which may be what you're saying as well.
-- Markus
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