问题
I have my reducer with a starting state of an empty array:
folderReducer(state:Array<Folder> = [], action: Action)
I'd like to populate the starting state, so when I do
store.subscribe(s => ..)
The first item I get comes from the database. I assume the way of doing this is with ngrx/effects, but I'm not sure how.
回答1:
Your store always has the initial state, that you define in the reducer-function. The initial states main purpose is to ensure that the application is able to start up and not run into any null-pointer-exceptions. And also it sets up your application to start making the first api-calls ect. - so you can think of it as a technical initial state.
If you want to fill your store with api-data on the startup, you would do that on the same way that you add/modify data during any other action - just that the action of "initially loading data" is not triggered by some user-interaction but through:
- either when your root-component loads
- or as part of a service in the constructor
In case you want to prevent specific components from showing anything until your API-call is done, you would have to adjust the display-components to display or hide data based on your state (e.g. by implementing a flag in your satet initialDataLoaded).
回答2:
A dynamic initial state is now supported, see: https://github.com/ngrx/platform/blob/master/docs/store/api.md#initial-state-and-ahead-of-time-aot-compilation
Also see: https://github.com/ngrx/platform/issues/51
I would only do this if the database is local, otherwise the request will hold up loading of the application.
来源：https://stackoverflow.com/questions/42517257/ngrx-how-to-have-a-starting-state-from-an-api