The problem I'm trying to solve is that ParentLeaf is a header that displays some info, but the ChildLeafs are forms for different kind of entities, whose ident can resolve the attributes that the header in parentLeaf needs. When the url of a child is accessed directly the ident of the parentLeaf is not in the path params

The props are always a tree. If you have the parent props, then you also have the leaf.

in other words, the current route props are the tree of props of the current parent/child

no need to look for an ident…you have a denormalized tree.

I think I understand that, my issue is that the props needed by the parent are not loaded at that point, but the parent can do a load if it finds the ident of leaf

I am able to get what I want with the following snippet in a mutation done in the will-enter of the parent

(let [state @state]
            (loop [new-router-k router-k]
              (let [[k v :as ident] (or (get-in state [::dr/id new-router-k ::dr/current-route])
                                        (get-in state [::dr/id new-router-k ::dr/pending-route :target]))]
                (if (= ::dr/id k)
                  (recur v)
                  ident))))

In general I would not recommend tying loads to things this way. If you have a complex scenario, I highly recommend you put a UISM or statechart around it, and control it that way. Treat DR as a ui-only concern most of the time. The side-effect integration in DR is for very simple cases (start something when a route is entered), and should use the DR lifecycle hooks. Putting I/O in the router itself is seriously discouraged.

and popping idents in state that point to “nowhere” is also a pretty bad idea

Drive your UI and I/O from your logic. Logic drives data shape, which drives rendering as a pure function. Do not invert that except in very simple cases, or where there is literally no other way (e.g. focus an input). You’re sort of in a middle ground here. The logic of the DR is what you’re trying to sort of hook into, but it’s a really gray area. You’re trying to do something in a way it wasn’t designed for, which is making kind of a mess.

Thanks for the advice I'll look into using a uism to manage the initial loading then. I suppose what Im doing now is akin to it. When current-course (my parent is a Course) is set I route immediately in the parent, when not i defer to a mutation that looks into the routers to find the current target and load the parent info from that target and sets the current course. On parent will unmount I unset the current-course

Great advice! Recorded for posterity in https://gist.github.com/holyjak/da15f613376bf7015385a7cd899ee3e8#tony-on-dynamic-routing-io-and-complexity-2023-03-18 🙂

Yes, the book is wrong. There is a prop called :current-state that is passed in. See the docstring of defrouter.