I have a page on which data is initialized via async fetch:
async fetch() {
const res = await requestApi(this, '/database');
this.sliderData = res.homeSlider;
this.modelData = res.model;
...
}
Then this data is thrown into the child components through the props, but since there are child components of level 3-4, it becomes not convenient to use the props with page. Is it possible to use provide/inject in this case? Moreover, it is important that the transmitted data is reactive. Objects always come from the request when trying to use provide/inject:
provide() {
return {
sliderData: this.sliderData
};
}
The data did not have time to be initialized and an empty object was sent.
I'm not sure that this is the best idea, but you can add a variable (for example isLoading: true) to your data; when all data you need is loaded change this.isLoading = false; additionally, add v-if="!isLoading" to the parent component. In this case, your child component will inject already loaded sliderData.
Related
I am building an application with storefront, which uses nextJS. I am able to use getServerSide props while loading a new page.
The page contains many components, each needing their own data. At the moment, I am getting all of these into a results array and then returning from getServerSideProps, as shown below.
export async function getServerSideProps({query}) {
let sid = query.shop
let promises = []
promises.push(getShopCategories(sid))
promises.push(getShopInfo(sid))
promises.push(offersFromShop(sid))
try {
let allPromises = Promise.all(promises)
let results = await allPromises;
//console.log("Shop Info:", results[1])
return {props: {
id: sid,
shopCategories: results[0],
shopInfo: results[1],
offers4u: results[2].products
}}
} catch(e) {
console.error("Failure:", e)
return { props: {}}
}
}
But in this way, I have to get the data needed for all components in one shot. I was thinking, how to let each sub component in the page to have its own 'getServerSideProps'.
I can implement this in each component, but I am unsure about passing the parameters needed (such as shopId, productId etc., which I would have fetched in the main page).
One way is to use cookies, so that the server side can pick up these values. Is there a better solution?
getServerSideProps is only available on direct component under page folder
If you want to fetch more data on sub-component in the page, consider using the useEffect hook or componentDidMount for that work.
Given the code below, my child component alerts trigger before any of the code in the Parent mounted function.
As a result it appears the child has already finished initialization before the data is ready and therefor won't display the data until it is reloaded.
The data itself comes back fine from the API as the raw JSON displays inside the v-card in the layout.
My question is how can I make sure the data requested in the Parent is ready BEFORE the child component loads? Anything I have found focuses on static data passed in using props, but it seems this completely fails when the data must be fetched first.
Inside the mounted() of the Parent I have this code which is retrieves the data.
const promisesArray = [this.loadPrivate(),this.loadPublic()]
await Promise.all(promisesArray).then(() => {
console.log('DATA ...') // fires after the log in Notes component
this.checkAttendanceForPreviousTwoWeeks().then(()=>{
this.getCurrentParticipants().then((results) => {
this.currentP = results
this.notesArr = this.notes // see getter below
})
The getter that retrieves the data in the parent
get notes() {
const newNotes = eventsModule.getNotes
return newNotes
}
My component in the parent template:
<v-card light elevation="">
{{ notes }} // Raw JSON displays correctly here
// Passing the dynamic data to the component via prop
<Notes v-if="notes.length" :notesArr="notes"/>
</v-card>
The Child component:
...
// Pickingn up prop passed to child
#Prop({ type: Array, required: true })
notesArr!: object[]
constructor()
{
super();
alert(`Notes : ${this.notesArr}`) // nothing here
this.getNotes(this.notesArr)
}
async getNotes(eventNotes){
// THIS ALERT FIRES BEFORE PROMISES IN PARENT ARE COMPLETED
alert(`Notes.getNotes CALL.. ${eventNotes}`) // eventNotes = undefined
this.eventChanges = await eventNotes.map(note => {
return {
eventInfo: {
name: note.name,
group: note.groupNo || null,
date: note.displayDate,
},
note: note.noteToPresenter
}
})
}
...
I am relatively new to Vue so forgive me if I am overlooking something basic. I have been trying to fix it for a couple of days now and can't figure it out so any help is much appreciated!
If you are new to Vue, I really recommend reading the entire documentation of it and the tools you are using - vue-class-component (which is Vue plugin adding API for declaring Vue components as classes)
Caveats of Class Component - Always use lifecycle hooks instead of constructor
So instead of using constructor() you should move your code to created() lifecycle hook
This should be enough to fix your code in this case BUT only because the usage of the Notes component is guarded by v-if="notes.length" in the Parent - the component will get created only after notes is not empty array
This is not enough in many cases!
created() lifecycle hook (and data() function/hook) is executed only once for each component. The code inside is one time initialization. So when/if parent component changes the content of notesArr prop (sometimes in the future), the eventChanges will not get updated. Even if you know that parent will never update the prop, note that for performance reasons Vue tend to reuse existing component instances when possible when rendering lists with v-for or switching between components of the same type with v-if/v-else - instead of destroying existing and creating new components, Vue just updates the props. App suddenly looks broken for no reason...
This is a mistake many unexperienced users do. You can find many questions here on SO like "my component is not reactive" or "how to force my component re-render" with many answers suggesting using :key hack or using a watcher ....which sometimes work but is almost always much more complicated then the right solution
Right solution is to write your components (if you can - sometimes it is not possible) as pure components (article is for React but the principles still apply). Very important tool for achieving this in Vue are computed propeties
So instead of introducing eventChanges data property (which might or might not be reactive - this is not clear from your code), you should make it computed property which is using notesArr prop directly:
get eventChanges() {
return this.notesArr.map(note => {
return {
eventInfo: {
name: note.name,
group: note.groupNo || null,
date: note.displayDate,
},
note: note.noteToPresenter
}
})
}
Now whenever notesArr prop is changed by the parent, eventChanges is updated and the component will re-render
Notes:
You are overusing async. Your getNotes function does not execute any asynchronous code so just remove it.
also do not mix async and then - it is confusing
Either:
const promisesArray = [this.loadPrivate(),this.loadPublic()]
await Promise.all(promisesArray)
await this.checkAttendanceForPreviousTwoWeeks()
const results = await this.getCurrentParticipants()
this.currentP = results
this.notesArr = this.notes
or:
const promisesArray = [this.loadPrivate(),this.loadPublic()]
Promise.all(promisesArray)
.then(() => this.checkAttendanceForPreviousTwoWeeks())
.then(() => this.getCurrentParticipants())
.then((results) => {
this.currentP = results
this.notesArr = this.notes
})
Great learning resource
What is the current idiomatic way to lazy load properties when using MobX?
I've been struggling with this for a few days, and I haven't found any good examples since strict mode has become a thing. I like the idea of strict mode, but I'm starting to think lazy-loading is at odds with it (accessing, or observing a property should trigger the side effect of loading the data if it's not already there).
That's the crux of my question, but to see how I got here keep reading.
The basics of my current setup (without posting a ton of code):
React Component 1 (ListView):
componentWillMount
componentWillMount & componentWillReceiveProps - the component gets filter values from route params (react-router), saves it as an observable object on ListView, and tells the store to fetch 'proposals' based on it
Store.fetchProposals checks to see if that request has already been made (requests are stored in an ObservableMap, keys by serializing the filter object so two identical filters will return the same response object). It makes the request if it needs to and returns the observable response object that contains info on whether the request is finished or has errors.
ListView saves the observable response object as a property so it can display a loading or error indicator.
ListView has a computed property that calls Store.getProposals using the same filter object used to fetch
Store.getProposals is a transformer that takes a filter object, gets all proposals from an ObservableMap (keys on proposal.id), filters the list using the filter object and returns a Proposal[] (empty if nothing matched the filter, including if no proposals are loaded yet)
This all appears to work well.
The problem is that proposals have properties for client and clientId. Proposal.clientId is a string that's loaded with the proposal. I want to wait until client is actually accessed to tell the store to fetch it from the server (assuming it's not already in the store). In this case ListView happens to display the client name, so it should be loaded shortly after the Proposal is.
My closest I've gotten is setting up a autorun in the Proposal's constructor list this, but part of it is not reacting where I'm indending. (truncated to relevant sections):
#observable private clientId: string = '';
#observable private clientFilter: IClientFilter = null;
#observable client: Client = null;
constructor(sourceJson?: any) {
super(sourceJson);
if (sourceJson) {
this.mapFromJson(sourceJson);
}
//this one works. I'm turning the clientId string into an object for the getClients transformer
autorun(() => { runInAction(() => { this.clientFilter = { id: this.clientId }; }) });
autorun(() => {
runInAction(() => {
if (this.clientId && this.clientFilter) {
const clients = DataStore.getClients(this.clientFilter);
const response = DataStore.fetchClients(this.clientFilter);
if (response.finishedTime !== null && !response.hasErrors) {
this.client = clients[0] || null;
console.log('This is never called, but I should see a client here: %o', DataStore.getClients(this.clientFilter));
}
}
})
});
}
The response object is observable:
export class QueryRequest<T extends PersistentItem | Enum> {
#observable startTime: Date = new Date();
#observable finishedTime: Date = null;
#observable errors: (string | Error)[] = [];
#observable items: T[] = [];
#computed get hasErrors() { return this.errors.length > 0; }
#observable usedCache: boolean = false;
}
I'm getting the feeling I'm fighting the system, and setting up autoruns in the constructor doesn't seem ideal anyway. Anyone solve this pattern in a reasonable way? I'm open to suggestions on the whole thing if my setup looks crazy.
EDIT 1: removed #Mobx for clarity.
EDIT 2:
Trying to re-evaluate my situation, I (again) found the excellent lib mobx-utils, which has a lazyObservable function that may suite my needs. Currently it's looking like this:
client = lazyObservable((sink) => {
autorun('lazy fetching client', () => {
if (this.clientFilter && this.clientFilter.id) {
const request = DataStore.fetchClients(this.clientFilter);
if (request.finishedTime !== null && !request.hasErrors) {
sink(request.items[0]);
}
}
})
}, null);
This is working!
I think I need the autorun in there to update based on this objects clientId/clientFilter property (if this object is later assigned to a new client I'd want the lazyObservable to be updated). I don't mind a little boilerplate for lazy properties, but I'm, definitely open to suggestions there.
If this ends up being the way to go I'll also be looking at fromPromise from the same lib instead of my observable request object. Not sure because I'm keeping track of start time to check for staleness. Linking here in case someone else has not come across it:)
I've been using a different approach in my projects and I extracted it into a separate npm package: https://github.com/mdebbar/mobx-cache
Here's a quick example:
First, we need a React component to display the client info:
#observer
class ClientView extends React.Component {
render() {
const entry = clientCache.get(this.props.clientId)
if (entry.status !== 'success') {
// Return some kind of loading indicator here.
return <div>Still loading client...</div>
}
const clientInfo = entry.value
// Now you can render your UI based on clientInfo.
return (
<div>
<h2>{clientInfo.name}</h2>
</div>
)
}
}
Then, we need to setup the clientCache:
import MobxCache from "mobx-cache";
function fetchClient(id) {
// Use any fetching mechanism you like. Just make sure to return a promise.
}
const clientCache = new MobxCache(fetchClient)
That's all you need to do. MobxCache will automatically call fetchClient(id) when it's needed and will cache the data for you.
Based on the scaffolder mern.io I was going through the code to see what was going on. I stumbled upon a .need method which looks like something related to es6 classes. I can't seem to find any usable info anywhere, so I ask what is the .need method?
class PostContainer extends Component {
//do class setup stuff here
}
PostContainer.need = [() => { return Actions.fetchPosts(); }];
You can get the project up and running very easily with these commands.
npm install -g mern-cli
mern YourAppName
The mern documentation is pretty terse when it comes to explaining this.
fetchComponentData collects all the needs (need is an array of actions that are required to be dispatched before rendering the component) of components in the current route. It returns a promise when all the required actions are dispatched.
Reading through the code is a much clearer way of finding out what's going on here.
Overview
It's a way to specify some actions that should be dispatched before rendering the component.
This component maps the posts property from the Redux store to a prop called posts so that it can render the list of posts.
// PostContainer.jsx
function mapStateToProps(store) {
return {
posts: store.posts,
};
}
However, initially this property will be empty because the posts need to be fetched from an asynchronous API.
// reducer.js
// initial state of the store is an empty array
const initialState = { posts: [], selectedPost: null };
This component needs the posts to be available before it renders, so it dispatches the action returned from the call to Actions.fetchPosts().
// actions.js
export function fetchPosts() {
return (dispatch) => {
return fetch(`${baseURL}/api/getPosts`).
then((response) => response.json()).
then((response) => dispatch(addPosts(response.posts)));
};
}
When the action has finished dispatching, the store's data can be mapped to the connected component.
Caveat
This isn't a universal way to specify asynchronous dependencies for React components. It only works because mern has a utility method called fetchComponentData that it calls at the server side, in order to populate the Redux store before rendering.
// server.js
fetchComponentData(store.dispatch, renderProps.components, renderProps.params)
This method traverses the components from the second argument to extract the needs from each. Then it executes 'needs` and waits for all the promises to complete.
// fetchData.js
const promises = needs.map(need => dispatch(need(params)));
return Promise.all(promises);
When the promise returned by Promise.all(promise) completes, the Redux store will be populated and the components can safely render their data to be served to the client.
Syntax
You mentioned that you thought it might be related to ES6 classes, so I'll cover the syntax quickly too.
ES6 classes can't have static properties specified in the class literal, instead we have to declare them as properties on the class after it has been defined.
The needs property must be an array of functions that return promises to work with fetchComponentData. In this case we have an arrow function declared inside an array literal. It might help to look at it split up into separate variables.
const fetchPosts = () => { return Actions.fetchPosts() };
const needs = [fetchPosts];
PostContainer.need = needs;
ReactJS, Baobab, Material-UI app displays some items, identified by their numeric id. To display those, title and image url's are retrieved from a remote service via ajax. Tree branch stores that data:
data: {
12345: {title:'ABC', image:'https://...'}, // id is 12345
12346: {...
}
Upon item component creation and first rendering, its extended data may, or may not be already available in the tree. If its not, ajax call is enqueued to receive that data. It might happen that multiple items are created with the same item id.
To avoid extra requests for the same id, I want to put a dummy info {title:'loading', image:'spinner.gif'} into the tree upon the first request to that id's info. Thus this data will be used for the very first render(). Successive components would get that dummy info, and will not initiate any extra requests.
Question: how, and where can I place the code to test if the tree has no info yet and place the dummy there to indicate its "penging" state and enqueue the request?
Tried so far:
component's constructor – props are not set there yet;
componentWillMount() – the first render started with the old state of the tree, despite the tree.commit() after setting the dummy value;
in the branch function that dynamically creates components cursor pointing to its data. Got warning:
setState(...): Cannot update during an existing state transition (such as within render). Render methods should be a pure function of props and state.
This can be solved one level up – once the list of ids is available. But it feels right that a component should be able to handle its data within itself.
Please advice a correct way to immediately update Baobab tree data before the first render of a React Component, from within that Component?
In my case (i am use same stack) wrap branch work fine.
import BaobabPropTypes from 'baobab-react/prop-types';
class Actions {
/**
* #param {Baobab} tree
*/
static prefetchTree = (tree) => {
tree.select(somePath).set(defaultValue);
tree.commit();
};
}
class Page extends React.Component {
static contextTypes = {
tree: BaobabPropTypes.baobab
};
componentWillMount() {
Actions.prefetchTree(this.context.tree);
}
render() {
return <Branch {...this.props}/>;
}
}
Baobab has a get event, use it to detect requests that return values that are not fetched yet:
tree.on('get', function(e) {
if (e.data.data === undefined) {
const path = e.data.path; // requested cursor path like ['data',12345]
const id = path[1];
FETCH_DATA(id)
.then( data => tree.set(path , data) );
tree.set(path, PLACEHOLDER_DATA);
}