re-frame is an entirely different framework
(https://github.com/Day8/re-frame/wiki/Solve-the-CPU-hog-problem). I
am not stating this can't be solved in om, only that you need to build
your own solution where as in re-frame it is taken care off. FWIW, I
solved this in om by writing the calculated data to app-state.
In om, a component won't be rendered if the 'related data' hasn't
changed, so it is fine to do something like:
(defn thin-row [{:keys [a b]} owner]
(reify ...
(render ... (html [:tr [:td (some-very-expensive-calculation-for
a)] [:td b]])))
(defn table [sequence-of-fat-maps owner]
(reify...
(render ... (html [:table [:tbody (om/build-all thin-row (map
(partial select-keys [:a :b]) sequence-of-fat-maps))]))
(as untested as it can possibly be and assuming saloon html)
My understanding is that om will render the 'table' but it will only
call 'thin-row' for each of the rows where 'a' or 'b' have actually
changed. For those where the input to 'thin-row' is the same, om will
instruct react that they haven't changed and thus
(some-very-expensive-calculation-for) is skipped. In this scenario you
would also want to add a unique key to each row as well.
On 25 March 2015 at 12:22, Andrew S <[email protected]> wrote:
> Thanks Colin. Couple of followups:
>
> 1) What is re-frame? I couldn't find that on the Om documentation page.
>
> 2) If I have a parent observe an entire reference cursor (or any cursor for
> that matter), then wouldn't the parent re-render when any individual
> key/value in the reference cursor updates? And thus if the parent re-renders,
> then doesn't this mean the parent re-renders all of its children? Perhaps I
> don't entirely understand the render tree process in Om, but I thought if a
> component re-renders, then it would also re-render any other components it
> creates/builds. If only one of my children actually needs an updated value,
> then the entire parent re-rendering is a waste and the sort of thing I'm
> trying to get around.
>
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