re-frame/docs/Basic-App-Structure.md

## Simpler Apps

To build a re-frame app, you:
  - design your app's data structure (data layer)
  - write and register subscription functions (query layer)
  - write Reagent component functions (view layer)
  - write and register event handler functions (control layer and/or state transition layer)

For simpler apps, you should put code for each layer into separate files:
```
src
├── core.cljs         <--- entry point, plus history, routing, etc
├── db.cljs           <--- schema, validation, etc  (data layer)
├── subs.cljs         <--- subscription handlers  (query layer)
├── views.cljs        <--- reagent components (view layer)
└── events.cljs       <--- event handlers (control/update layer)
```

For a living example of this approach, look at the [todomvc example](https://github.com/Day8/re-frame/tree/master/examples/todomvc).

### There's A Small Gotcha

If you adopt this structure there's a gotcha. 

`events.cljs` and `subs.cljs` will never be `required` by any other 
namespaces. To the Google Closure dependency mechanism it appears as 
if these two namespaces are not needed and it doesn't load them.

And, if the code does not get loaded, the registrations in these namespaces
never happen. You'll then be baffled as to why none of your events handlers 
are registered.

Once you twig to what's going on, the solution is easy.  You must 
explicitly `require` both namespaces, `events` and `subs`, in your `core` 
namespace. Then they'll be loaded and the registrations will occur 
as that loading happens. 

## Larger Apps

Assuming your larger apps has multiple "panels" (or "views") which are 
relatively independent, you might use this structure:
```
src
├── panel-1
│   ├── db.cljs           <--- schema, validation, etc  (data layer)
│   ├── subs.cljs         <--- subscription handlers  (query layer)
│   ├── views.cljs        <--- reagent components (view layer)
│   └── events.cljs       <--- event handlers (control/update layer)
├── panel-2
│   ├── db.cljs           <--- schema, validation. etc  (data layer)
│   ├── subs.cljs         <--- subscription handlers  (query layer)
│   ├── views.cljs        <--- reagent components (view layer)
│   └── events.cljs       <--- event handlers (control/update layer)
.
.
└── panel-n
```

Continue to [Navigation](Navigation.md) to learn how to switch between panels of a larger app.