You're not missing anything. This is a fundamental issue in Om right now and I've been designing and working on a fix. Basically in the very near future a component will be able to access something in the application state without needing a parent component to pass it in from above.
The idea is that a component will be able to get its data directly from the app state with something like (om/get-shared owner [:app-state :foo]). Still working out the details, but this work is happening in the `ind-components` branch. When it's finished there'll be an accompanying nested tab view example - one of the cases that suffers the most under the current system. David On Wed, Apr 9, 2014 at 6:33 AM, Daniel Kersten <[email protected]> wrote: > Hi, > > I'm trying to figure out the best way of structuring complex applications > in Om and I've hit a bit of a brick wall that I'm hoping someone can help > me with. > > I like the concept of cursors - narrow down the application state to what > the individual components actually need and allow them to read and modify > only that. > > The problem I'm having is that I don't know how to structure my state so > that the correct components have access to everything they need. Its easy > if each component only requires a strict subset of its parent, which is > often the case, but not always. I've hit a scenario where a component needs > access to two very different branches of the app state and I'm not sure how > to pass it to the component that needs it. > > As a (contrived) example, imagine you had an app for displaying orders in > an online store and the application state is something like this: > > (def app-state (atom {:items [{:type "book" :price 123} {:type "cd" > :price 200}] > :orders [{:date xxx :type "book" :count 3} {:date > yyy :type "cd" :count 1}] > :filter "book"})) > > You can imagine that in a real application the :items and :orders branches > may be much deeper. > > Lets say I now have two components, one displaying the items (so it is > passed a cursor with path [:items]) and one displaying the orders (so it is > passed a cursor with path [:orders]). What if I now only want to display > items and orders where the type matches the filter? > > I have a few options: > > 1. Restructure the app state in a way that gives each component access > to what it needs. This is not ideal as it means that I'm modelling my state > after how its being rendered rather than how its being processed and makes > it very application specific. > 2. I can propagate the additional values down the component tree (eg > using the :state parameter to build), but this means that every other > component before the one that consumes it must now do additional work that > it shouldn't need to know about (couples the parent components too tightly > to the child one) > 3. Similarly, passing it in opts is not ideal as it has the same issue > as #2, with the added caveat that the component also won't rerender on > change. > 4. I can store the value in component local state and update it > through a core.async channel. This works well in the example above, where > one or two simple values need to be communicated, but gets unruly when the > application is more complex. > 5. I can pass the entire app state to each component (perhaps trough > shared state) and use transformation functions (similar to what Sean Grove > did in his recent slides) to transform the state into a local view for each > component. This means each component gets to select exactly what it needs > to access without worrying about what comes before or after it in the > hierarchy, but then you lose the benefit of cursors and automatic > re-rendering when something changes. > > > I'm sure I'm missing something! > > Any tips appreciated. > > Dan. > > -- > Note that posts from new members are moderated - please be patient with > your first post. > --- > You received this message because you are subscribed to the Google Groups > "ClojureScript" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To post to this group, send email to [email protected]. > Visit this group at http://groups.google.com/group/clojurescript. > -- Note that posts from new members are moderated - please be patient with your first post. --- You received this message because you are subscribed to the Google Groups "ClojureScript" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at http://groups.google.com/group/clojurescript.
