refactor(q): Update query handling with customizable result-set-fn

[mpenet]

Modified the q* function to enable reducing results via IReduceInit. Added a result-set-fn option in q to allow customization of query result transformations, defaulting to a vector (same as current behavior).

[blind shot, untested]

[andersmurphy]

Thanks for starting on this!

Just a heads up I'll be adding and caching the meta data for table, column name and alias which will probably be useful for this.

[mpenet]

Just a heads up I'll be adding and caching the meta data for table, column name and alias which will probably be useful for this.

Thanks for the info. I somewhat forgot about this pr :), blaming another side-project on that one. I ll try to get this moving during the holidays.

[andersmurphy]

@mpenet I needed this behaviour so I've finished it here (now on master).

It was a bit more involved to get the meta data, but your initial draft made it much easier, I had no idea about clojure.lang.IReduceInit. Really appreciate the help!

[mpenet]

Oh nice!
Something similar could be done with column -> make it a first class thing and allow to specify it as a 3 arity fn:

Something along those lines:

(defn row-generator
  [ctx] ; ctx is potentially useful to retrieve column metadata, ex col name
  (fn
    ([] (transient! []))
    ([row k v] (conj! row v))
    ([row] (persistent! row))))

[mpenet]

To expand on this: this would open the possibility to users to generate a map from a row, or do some more fancy things like pack values together, build records, etc...

It's quite common in db libraries, I used that here for instance: https://github.com/mpenet/alia/blob/master/modules/alia/src/qbits/alia/result_set.clj#L39-L42 (I did it with a Protocol of 3 fns, but a simple fn with 3 different arities would work just fine).