Support arbitrary expressions in sum_cache and sum_through_many_cache

[TSMMark]

Related Issue: #9

TODO:

• Support in sum_cache
• Support in sum_through_many_cache
• Use Sequel.lit for table names
• Documentation

[TSMMark]

@jeremyevans all set. lmk if you need anything else

[jeremyevans]

This looks mostly good, thanks for the patch.

However, one of the rules in Sequel development is to never attempt to parse SQL, because it's basically not possible to handle even simple cases correctly. What if summed_column is :NEW or :OLD?

The correct way to handle this is to use Sequel.lit('NEW') instead of :NEW (and likewise for :OLD), and remove the gsub calls.

I don't see any documentation updates for this. I think the documentation should probably be updated to show it is possible to use expressions in addition to columns.

With those issues fixed, I'll try to test this in the next few days, and assuming no problems it will be merged and a new gem released.

[TSMMark]

Thanks for the quick feedback! All taken care of and documentation added. Looking forward to the new release

[jeremyevans]

I've released 1.3.0 with this these commits. I rebased this pull request to get rid of the unnecessary merge commit, which is why this didn't get closed automatically. Thanks for your work on this!

[TSMMark]

Don't mention it! Thanks for shipping so quickly. Really awesome