On Tuesday, November 8, 2011 1:42:25 PM UTC-5, BrendanC wrote: > > In the case of computed columns it took me a while to understand the use > of the '_extra' construct. >
I agree. I'm working on better documentation of the use of expressions in general, and in selects (i.e., computed columns) in particular. Note, _extra is an implementation detail and not part of the API, so not promised to remain backward compatible. It is not needed when directly accessing data from Row objects, but as you have discovered, there are issues when converting to formats like JSON. Anthony
