>From Slack the answer is _not_ to do:
> (defn table-row [_]
> (fn [raw-row]
> (let [decorated-row (subscribe [:decorated-row (row)]
> [:tr [:td (:manager-desc @row)]])))
but rather:
> (defn table-row [row]
(let [decorated-row (subscribe [:decorated-row (row)]
>
> (fn [raw-row]
> [:tr [:td (:manager-desc @decorated-row)]])))
i.e. the let always goes outside the inner fn otherwise you get one
subscription per rendering which isn’t what you want.
Thanks Mike and profil
> On 24 Jul 2015, at 11:12, Colin Yates <[email protected]> wrote:
>
> Hi,
>
> I have a table component which iterates a list of entities and calls a row
> component passing in that entity. In concrete terms I have a bunch of
> 'customers' that contain a FK ID of their manager and I want to render the
> name of the manager.
>
> I need to decorate that entity with other things (resolving names of linked
> entities for example) and I can see a number of ways of doing that (hack code
> warning):
>
> [decorate the collection in a sub]
> Have a subscription which returns the decorated entities. This subscription
> would use other subscriptions to resolve the ids:
>
> (register-sub :results
> (fn [db]
> (let [raw-results (subscribe [:raw-results])
> managers (subscribe [:manager/by-id])]
> (reaction
> (map (fn [row] (assoc row :manager-desc (managers (:manager-id row)))
> @raw-results)))))
>
> The cost is that this subscription is re-evaluated for every row if either
> the raw-results or the manager changes.
>
> [decorate the collection in the component]
> (defn table-rows []
> (let [raw-results (subscribe [:raw-results])
> managers (subscribe [:manager/by-id])]
> (fn []
> (let [results (map (fn [row] (assoc row :manager-desc (managers
> (:manager-id row))) @raw-results)]
> (into [:tbody] (map table-row results)))
>
> The cost here is that the entire table is re-rendered every time either the
> managers or the raw-results change, however the table-row rendering should be
> short circuited for the non-changed rows.
>
> [decorate the collection in an entity-specific subscription]
> (register-sub :decorated-row
> (fn [db [_ row]
> (let [managers (subscribe [:manager/by-id])]
> (reaction
> (assoc row :manager-desc (managers (:manager-id row))))))
>
> (defn table-row [_]
> (fn [raw-row]
> (let [decorated-row (subscribe [:decorated-row (row)]
> [:tr [:td (:manager-desc @row)]])))
>
> (defn table-rows []
> (let [raw-results (subscribe [:raw-results])]
> (fn []
> (into [:tbody] (map table-row @raw-results))
>
> This feels the cleanest and changes are scoped to as small a change as
> possible.
>
> The fourth variation is the same as above except table-row doesn't delegate
> to a subscription rather it subscribes to the managers map and resolves it
> inline.
>
> What do you all consider 'idiomatic' and most performant?
>
> Thanks!
>
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