Hello this is my first question. I am trying to set up a project where modules along with the redux and sagas will be injected into the main app, using redux-injectors. In my sagas I want to use yield select, to check if an action has updated the state and then carry on. For example, when I post an image, I want to make sure there were no errors in posting the file and then move on. I use the following function:
export const imageErrors = (state: RootState): IImagesErrorState => state.image.errors
and then in the saga.ts file I use it as such:
if (imagesErrors?.postImageError !== null) {
throw imagesErrors.postImageError
}
this works fine as long as the state.image exists in the root state from the beginning. However, how do I do that when I want to inject this state later on using useInjectReducer and useInjectSaga? I obviously get an error
Property 'image' does not exist on type 'Reducer<CombinedState<{ user: CombinedState<{ auth: IAuthState; errors: IErrorState; }>; }>, AnyAction>'.ts(2339)
So how do we handle selectors of specific pieces of state, since state does not yet include them?
Thank you so much.
Can't talk about the Typescript part of things, but in terms of architecture you've got two options.
One is the obvious - that is to add conditions or ? everywhere to avoid errors from accessing missing properties, but that can get tedious quickly.
The other probably better option is to rethink your state & application chunks. What is this saga that is accessing state that isn't existing yet? Does it need to run before you have such state? If not, let's move the saga to the same chunk as the reducer. In the opposite case, where you need the saga to be running e.g. as part of the runtime chunk, then perhaps the image state should be in the runtime chunk as well.
Related
I asked a question here recently about observables and you guys were of really great help (as always). Now I'm having a similar situation, and me and my team-mate are bending our brains over it.
The bug to fix was: user sees a collection of assets, and on browser refresh the wrong set of assets was being loaded. It turns out the key to the problem was one particular pipe observing the currently selected collection. Here's the relevant code:
this.selectedCollection.pipe(
filter((v) => !!v)).subscribe((v) => {
console.log('PIPE: selected collection', v.collectionId);
this.store.dispatch(
// action jackson on redux
)
);
});
The action to be dispatched here is for loading the assets of the collection. One collection was always loaded first as default and it was conflicting with further selections made by the user.
I've also added console.logs on the relevant reducers and effect to visualize behavior.
What happens on browser refresh is this:
Collection 9-em... is the default collection we don't want to see, and collection 9uem... is the user's choice whose asset's we want to see.
The first five lines show the expected output of the observable:
default collection set as selected collection
reducer 'is loading' assets
the user triggers a change selected collection action
the selected collection value is being updated and emitted accordingly
Now we would have expected the effect to load the assets and that's it. But what happens is that the pipe keeps emitting the same values once again, which is weird, because I'm 100% sure no further value is being set from anywhere. But it would also be fine, since we end up with the desired value. Yet strangely, the reducer is handling the load actions in reverse order, which led to the wrong assets being loaded (this could be a whole different issue on top).
Adding auditTime(200) as first operator to the pipe above fixed the issue. No further values were emitted.
Now, my questions are:
Why are the values emitted twice? Could it be an inappropriate operator/subscription some place else (didn't see anything suspicious)?
And why is auditTime(200) magically fixing this?
The effect also works as a pipe of actions being filtered, and it contains an auditTime(200) operator before executing, so that it executes only on the last action. While I do understand on principle what it does, I'm not quite sure if using auditTime like that just because it works is such a good idea.
I assume this is an issue out of noob confusion resulting in using rxjs not the right way. Unfortunately, I couldn't find anything useful on google. I really don't like 'fixing' a bug by adding a line of code that I just don't understand.
Thank you so much in advance!
As requested by fridoo, here's the code for this.selectedCollection:
get selectedCollection(): Observable<collectionState.CollectionsData> {
return this.store
.select(collectionState.getSelectedCollection)
.pipe(distinctUntilChanged());
}
And for getSelectedCollection:
export const getSelectedCollection: (state: any) => CollectionsData = (state: any) =>
getCollectionsState(state)
? getCollectionsState(state).selectedCollection
: undefined;
The rest is pretty forward just objects of state, the observable created via the select method. We're not using any library for redux (not my decision), so select is implemented like this:
select<T>(fn: (state: any) => T): Observable<T> {
return this.state$.pipe(map(fn), distinctUntilChanged());
}
Does this help any further?
I have what I believe is a very common scenario... I'm building a dashboard of components that will be driven by some datasource. At the top of the view would be a series of filters (e.g. a date range). When the date range is updated, the components on the screen would need to update their data based on the selected range. This would in turn force the individual components that are slave to that picker to need to fetch new data (async action/XHR) based on the newly selected range.
There can be many components on the screen and the user may wish to add/remove available displays, so it is not as simple as always refreshing the data for all components because they may or may not be present.
One way I thought to handle this was in the action dispatched when a new date range is selected was to figure out what components are on screen (derived from the Store) and dispatch async actions to fetch the data for those components. This seems like a lot of work will go into the DATE_CHANGED action.
Another alternative might be to detect date range changes in store.subscribe() callbacks from each of the components. This seems to decouple the logic to fetch the data from the action that caused this to happen. However, I thought it was bad practice (or even an error) to dispatch while dispatching. Sure I can wrap it in a setTimeout, but that feels wrong too.
Third thing that came to mind was just doing fetch calls directly in the component's store.subscribe() and dispatching when those return, but I thought this breaks the connect model.
This seems like a common pattern to fetch based on state changes, but I don't know where its best to put those. Any good documentation / examples on the above problem?
Don't use store.subscribe for this. When DATE_CHANGED reaches the reducer it's meant for, simply change the application state (I'm assuming the date range is part of the store somehow). So you have something like state.rangeStart and state.rangeEnd.
You didn't mention what view rendering library you're using, so I can only describe how this is typically done with React:
The components know wether they are currently mounted (visible) or not, so redux doesn't need to be concerned with that. What you need is a way to detect that state.rangeStart or state.rangeEnd changed.
In React there is a lifecycle hook for that (componentWillReceiveProps or getDerivedStateFromProps in the newest release). In this handler you dispatch async redux actions that fetch the data the component needs. Your view library will probably have something similar.
The components display some kind of "empty" or "loading" state while you're waiting for the new data typically. So a good practice is to invalidate/clear data from the store in the reducer that handles the DATE_CHANGED action. For example, if state.listOfThings (an array) entirely depends on the date range, you would set it to an empty array as soon as the date changes: return { ...state, listOfThings: [] }. This causes the components to display that data is being fetched again.
When all the async redux actions went through the REQUEST -> SUCCESS/FAILURE cycle and have populated the store with the data, connected components will automatically render it. This is kind of its own chapter, look into redux async actions if you need more information.
The tricky part are interdependencies between the components and the application they're rendering. If two different dashboard components for example want to fetch and render state.listOfThings for the current date range, you don't want to fetch this data twice. So there needs to be a way to detected that 1) the data range has changed but also 2) a request to fetch listOfThings is already on its way. This is usually done with boolean flags in the state: state.isFetchingListOfThings. The async actions fetching this data cause the reducer to set this flag to true. Your components need to be aware of this and dispatch actions conditionally: if (props.rangeStart !== nextProps.rangeStart && !nextProps.isFetchingListOfThings) { props.fetchListOfThings(); }.
The store has a method called getState that will return the current state of the store.
What prevents code somewhere in my application from (accidentally) modifying the returned state from store?
Let's say i call this:
let state = store.getState();
state.someProperty = 'fun';
The implementation that i've found on getState on the store object simply returns the inner state object that gets overwritten with each new action.
const getState = () => state;
In between actions/new states what prevents code from modifying the state that will be read by another subscriber? In my above example, setting someProperty to 'fun' will persist inside the store on the state property, until overwritten.
While i'm obviously not supposed to modify the state, a simple mistake might bind the state to some component that (unknowingly) modifies its inputs - perhaps on a 2-way binding in an angular environment?
<app-some-component [user]="state"></app-some-component>
Shouldn't getState() be implemented as a clone of its state model?
P.S. This is not specifically related to Angular - which is why i didn't add the tag - to allow more people not used to Angular to answer the question.
The answer is: nothing :)
The core Redux library itself technically doesn't actually care if state gets mutated or not. You could actually mutate in your reducers, or have other parts of your app get the state tree and mutate it, and the store itself wouldn't know or care.
However, mutation will break time-travel debugging, as well as make tests unreliable. Even more importantly, the React-Redux library assumes that you will handle your state immutably, and relies on shallow equality comparisons to see if the state has changed. (This is the reason why "Why isn't my component re-rendering?" is in the Redux FAQ. 99.9% of the time, it's due to accidental mutation.)
If you are concerned about mutation, you can use a library like Immutable.js instead of plain JS objects, or use one of the several tools for freezing your state in development to catch mutations.
Project (Todolist) was created with immutable library, source here
Store structure: project have many tasks, In redux store: State - map, projects, tasks - Records
When I asyncly remove project ...
export const removeProject = project => (dispatch) => {
if (!isProjectExist(project)) return Promise.resolve()
return projectService
.delete(project)
.then(
() => {
dispatch(remove(project))
console.log("post removeProject resolved")
},
handleError,
)
}
.... that was created after initialization - it will be deleted and properly unmounted, but when project was passed as initialState - ProjectList will not be rerendered, and ProjectItem try to render itself with stale data, and fail, as in picture
It have tests
It looks like reducer returs changed data, but I use immutablejs, and previously i use normalizr-immutable, but I thought that source of issue in this library and write my own normalizeInitialState (source), it did not help, now I think that maybe source of problem in redux-immutable
I struggled entire day on solving of this problem
creator of redux says
I don't think this is something we can fix. React state changes are
asynchronous and React may (or may not) batch them. Therefore, the
moment you press “Remove”, the Redux store updates, and both Item and
App receive the new state. Even if the App state change results in
unmounting of Items, that will happen later than mapStateToProps is
called for Item.
Unless I'm mistaken, there is nothing we can do. You have two options:
Request all required state at App (or a lower, e.g. ItemList) level
and pass it down to “dumb” Items. Add safeguards to mapStateToProps
for “currently unmounting” state. For example, you may return null
from render in this case. Potentially we could have the component
generated by connect() return null from its render if mapStateToProps
returned null. Does this make any sense? Is this too surprising?
Hm, I never saw stubs like return (<div></div>) or safeguards in mapStateToProps in others code
markerikson
I'm not entirely sure I follow what exactly your problem is, but as a
guess: it sounds like the child component is re-rendering before the
parent is. This is a known issue with React-Redux v4 and earlier. The
v5 beta fixes that issue. Try installing react-redux#next and see if
that takes care of your problem.
I'm using Redux to write a NodeJS app. I'm interested in allowing users to dynamically load middleware by specifying it at runtime.
How do I dynamically update the middleware of a running Redux application to add or remove middleware?
Middleware is not some separate extension, it's part of what your store is. Swapping it at runtime could lead to inconsistencies. How do you reason about your actions if you don't know what middleware they'll be run through? (Keep in mind that middlewares don't have to operate synchronously.)
You could try a naive implementation like the following:
const middlewares = [];
const middlewareMiddleware = store => next => act => {
const nextMiddleware = remaining => action => remaining.length
? remaining[0](store)(nextMiddleware(remaining.slice(1)))(action)
: next(action);
nextMiddleware(middlewares)(act);
};
// ... now add/remove middlewares to/from the array at runtime as you wish
but take note of the middleware contract, particularly the next argument. Each middleware receives a "pass to the next middleware" function as part of its construction. Even if you apply middlewares dynamically, you still need to tell them how to pass their result to the next middleware in line. Now you're faced with a loss-loss choice:
action will go through all of the middleware registered at the time it was dispatched (as shown above), even if it was removed or other middleware was added in the meantime, or
each time the action is passed on, it goes to the next currently registered middleware (implementation is a trivial excercise), so it's possible for an action to go through a combination of middlewares that were never registered together at a single point in time.
It might be a good idea to avoid these problems alltogether by sticking to static middleware.
Use redux-dynamic-middlewares
https://github.com/pofigizm/redux-dynamic-middlewares
Attempting to change middleware on-the-fly would violate the principle of 'pure' actions and reducer functions, because it introduces side-effects. The resulting app will be difficult to unit-test.
Off the top of my head, it might be possible to create multiple stores (one for each possible middleware configuration), and use a parent store to provide the state switch between them. You'd move the data between the sub-stores when switching. Caveat: I've not seen this done, and there might be good reasons for not doing it.