I'm trying to build a component that retrieves a full list of users from Amazon AWS/Amplify, and displays said results in a table via a map function. All good so far.
However, for the 4th column, I need to call a second function to check if the user is part of any groups. I've tested the function as a button/onClick event - and it works (console.logging the output). But calling it directly when rendering the table data doesn't return anything.
Here is what I've included in my return statement (within the map function)
<td>={getUserGroups(user.email)}</td>
Which then calls this function:
const getUserGroups = async (user) => {
const userGroup = await cognitoIdentityServiceProvider.adminListGroupsForUser(
{
UserPoolId: '**Removed**',
Username: user,
},
(err, data) => {
if (!data.Groups.length) {
return 'No';
} else {
return 'Yes';
}
}
);
};
Can anyone advise? Many thanks in advance if so!
Because you should never do that! Check this React doc for better understanding of how and where you should make AJAX calls.
There are multiple ways, how you can solve your issue. For instance, add user groups (or whatever you need to get from the backend) as a state, and then call the backend and then update that state with a response and then React will re-render your component accordingly.
Example with hooks, but it's just to explain the idea:
const [groups, setGroups] = useState(null); // here you will keep what "await cognitoIdentityServiceProvider.adminListGroupsForUser()" returns
useEffect(() => {}, [
// here you will call the backend and when you have the response
// you set it as a state for this component
setGroups(/* data from response */);
]);
And your component (column, whatever) should use groups:
<td>{/* here you will do whatever you need to do with groups */}</td>
For class components you will use lifecycle methods to achieve this (it's all in the documentation - link above).
Related
According to the documentation of SWR: React Hooks for Data Fetching, there is an options object which can be passed in for more control of the hook.
The documentation mentions a compare option:
compare(a, b): comparison function used to detect when returned data
has changed, to avoid spurious rerenders. By default, dequal is used.
Is it something like this?
export function useUser(shouldAPIBeCalled = false) {
const { data: user, error, mutate } = useSWR(() => shouldAPIBeCalled ? '/api/user' : null, fetcher, {
compare: (_old, _new) => {
return dequal(_old, _new);
}
})
Essentially I don't want the fetcher to be called if we haven't changed the original object in my case:
If the user is still...
user: null // don't make that call again
Don't make another call because it hasn't changed!
What’s happening to me is the hook keeps firing.
I only have the hook in a Layout component to show hide navigation elements if we have a user or not,
In the submit function of the login to get the mutate function to update the user,
And in the Auth component (which wraps certain pages) to check if a user is authorized.
Thanks in advance!
i'm new to react please forgive me if i'm asking a dumb question.
The idea is to access the tweets array from context, find the matching tweet and then set it in the component's state to access the data.
However, the tweets array results empty even though i'm sure it's populated with tweets
const { tweets } = useContext(TweeetterContext)
const [tweet, setTweet] = useState({})
useEffect(() => {
loadData(match.params.id, tweets)
}, [])
const loadData = (id, tweets) => {
return tweets.filter(tweet => tweet.id == id)
}
return (stuff)
}
You are accessing context perfectly fine, and it would be good if you could share a code where you set tweets.
Independent of that, potential problem I might spot here is related to the useEffect function. You are using variables from external context (match.params.id and tweets), but you are not setting them as dependencies. Because of that your useEffect would be run only once at the initial creation of component.
The actual problem might be that tweets are set after this initial creation (there is some delay for setting correct value to the tweets, for example because of the network request).
Try using it like this, and see if it fixes the issue:
useEffect(() => {
loadData(match.params.id, tweets)
}, [match.params.id, tweets])
Also, not sure what your useEffect is actually doing, as it's not assigning the result anywhere, but I'm going to assume it's just removed for code snippet clarity.
I want to create react table component which values are derived from single array object. Is it possible to control the component from view side? My goal is that every user using this component in their web browsers share the same data via singleton view object.
Program modeling is like below.
Database - there are single database in server which contain extinct and independent values.
DataView - there are singleton View class which reflects Database's table and additional dependent data like (sum, average)
Table - I'll build react component which looks like table. And it will show View's data with supporting sorting, filtering, editing and deleting row(s) feature (and more). Also it dose not have actual data, only have reference of data from View(Via shallow copy -- This is my question, is it possible?)
My intentions are,
- When user changes value from table, it is queried to DB by View, and if succeed, View will refer updated data and change it's value to new value and notify to Table to redraw it's contents. -- I mean redraw, not updating value and redraw.
- When values in View are changed with DB interaction by user request, there are no need to update component's value cause the components actually dose not have values, only have references to values (Like C's pointer). So only View should do is just say to Component to redraw it's contents.
I heard that React's component prop should be immutable. (Otherwise, state is mutable) My goal is storing references to component's real value to it's props so that there are no additional operation for reflecting View's data into Table.
It is concept problems, and I wonder if it is possible. Since javascript dose not support pointer officially(Am I right?), I'm not sure if it is possible.
View class is like below,
const db_pool = require('instantiated-singleton-db-pool-interface')
class DataView {
constructor() {
this.sessions = ['user1', 'user2'] // Managing current user who see the table
this.data = [ // This is View's data
{id:1, name:'James', phone:'12345678', bank:2000, cash:300, total:2300,..},
{id:2, name:'Michael', phone:'56785678', bank:2500, cash:250, total:2300,..},
{id:3, name:'Tyson', phone:'23455432', bank:2000, cash:50, total:2300,..}
] // Note that 'total' is not in db, it is calculated --`dependent data`
}
notifySessionToUpdate(ids) {
// ids : list of data id need to be updated
this.sessions.forEach((session) => {
session.onNotifiedUpdateRow(ids) // Call each sessions's
})
}
requestUpdateRow(row, changed_value) {
// I didn't write async, exception related code in this function for simple to see.
update_result = db_pool.update('UPDATE myTable set bank=2500 where id=1')
if (update_result === 'fail') return; // Do Nothing
select_result = db_pool.select('SELECT * from myTable where id=1') // Retrieve updated single data which object scheme is identical with this.data's data
for (k in Object.keys(select_result)) {.ASSIGN_TO_row_IF_VALUE_ARE_DIFFERENT.} // I'm not sure if it is possible in shallow copy way either.
calc.reCalculateRow(row) // Return nothing just recalculate dependant value in this.data which is updated right above.
// Notify to session
this.notifySessionToUpdate([1]) // Each component will update table if user are singing id=1's data if not seeing, it will not. [1] means id:1 data.
return // Success
}
... // other View features
}
Regarding session part, I'm checking how to implement sessionizing(?) the each user and it's component who is communicating with server. So I cannot provide further codes about that. Sorry. I'm considering implementing another shallow copied UserView between React Component Table and DataView(And also I think it helps to do something with user contents infos like sorting preference and etc...)
Regarding DB code, it is class which nest it's pool and query interface.
My problem is that I'm not familiar with javascript. So I'm not sure shallow copy is actually implementable in all cases which I confront with.
I need to think about,
1. Dose javascript fully support shallowcopy in consistent way? I mean like pointer, guarantee check value is reference or not.
2. Dose react's component can be used like this way? Whether using props or state Can this be fullfilled?
Actually, I strongly it is not possible to do that. But I want to check your opinions. Seems it is so C language-like way of thinking.
Redraw mean re-render. You can expose setState() or dispatch() functions from Table component and call them on View level using refs:
function View() {
const ref = useRef();
const onDbResponse = data => ref.current.update(data);
return (
<Table ref={ ref } />
);
}
const Table = React.forwardRef((props, ref) => {
const [ data, setData ] = useState([]);
useImperativeHandler(ref, {
update: setData
});
...
});
Anyway i don't think it's a good practice to update like that. Why can't you just put your data in some global context and use there?
const Context = React.createContext({ value: null, query: () => {} });
const Provider = ({ children }) => {
const [ value, setValue ] = useState();
const query = useCallback(async (request) => {
setValue(await DB.request(request));
}, [ DB ]);
const context = { value, query };
return <Context.Provider value={ context }>{ children }</Context.Provider>;
}
const useDB = () => useContext(Context);
const View = () => {
const { request } = useDB();
request(...);
}
const Table = () => {
const { value } = useDB();
...
}
I faced with API problem in nuxt.js.
I'm fetching the data from an API with axios in the module of store 'category/'. Everything works fine in case of fetching data. Event list is displaying and data flow through the store and component. I dispatched my asynchronous data from an API to the mounted property in a component.To be brief, I cannot validate my route params.
I want to return true on validating the proper url
export default {
validate({params}) {
return this.currentCategory.some((category) => category === params.category)
// Where this.currentCategory is the array of strings that have to match route params
// params.category is because my dynamic file called '_category.vue' in 'pages/'
I logged on template how this code behave.This validation returns false, but after a moment it returns true(because of fetching). I tried to add the condition if(this.currentCategory.length > 1). I have tried a lot, but seriously I dont know what is happening there.
Finally, I found answer for my question
export default {
async validate({params}) {
const validateParam = await this.currentCategory.some((category) => category === params.category)
return validateParam
I have two async requests I am trying to fulfill, the second based upon the results of the first. The way I am trying to do this is by:
Listen for success of first action: actions.GetAllItems
Select out from the store the relevant items based on ID: this.store.select(selectors.getItemsById)
Map over the returned IDs so I can make the second call for each item in the array of IDs returned by the first call
Put results in redux store, render to view.
The way I have now does successfully put it in my redux store. However since it's just vanilla Array.map it doesn't return an observable. Which means the observable isn't stored in this.details$, which means it does not render in my template with {{ details$ | async | json }}
How can I achieve this secondary XHR call based upon the results of the first?
ngOnInit() {
this.store.dispatch(new actions.GetAllItems())
this.details$ = this.actions$.pipe(
ofType(actions.types.GetAllItemsSuccess),
mergeMap(() => {
return this.store.select(selectors.getItemsById); // filter to multiple items based on item ID
}),
map((items: models.IItemGeneralResponse[]) => {
items.map(item => { // sync map does not seem like it belongs in rxjs
this.store.dispatch(
new actions.GetItemDetail(item.id)
);
});
})
);
}
You are trying to do ngrx effects stuff in your angular component. Use effects to handle side effects (calls to the backend/fetching data from local storage etc...) and make your component to watch for a piece of your state via a selector. Let's summarize like this -
Your component [or your guard or resolver] will just dispatch an action to the store.
If you set up a reducer for that action then your reducer will be called first otherwise it will go to step 3
In your effect, you are watching for the dispatched action. Your effect will make the first call and then from the response of the first call, it will make the second call and then it will update the state in your store [or piece of the state] which is being watched by your component by dispatching the respective actions to the store.
This is a typical workflow [It may vary as per the need of the app but the basic idea remains the same]. So keeping the basic idea lets modify your code like this -
In your component
sliceOfState$: Observable<any>; //change the type of observabe as per your app
ngOnInit() {
this.store.dispatch(new actions.GetAllItems())
//this observable will be used to render your data on UI
//you can use various rxjs operators to transform your data before shoing to UI
this.sliceOfState$ = this.store.select(//your selector which gives you sliceOfState);
}
Now In your effect -
#Effect()
this.details$ = this.actions$.pipe(
ofType(actions.types.GetAllItems),
switchMap(() => {
//here you call API which makes the call to backend which return allItems
return this.yourServiceWhichGetAllItems.getAllItems();
}),
switchMap(allItems => {
//now for each item you need to get its detail
//so forkJoin all the observables which calls the backedn for each item
const obs$ = allItems.map(item => this.yourServiceWhichGetDetails.getItemDetail(item));
return forkJoin(obs$);
})
map(allItemsWithDetails => {
//here you should call your action which will update the state in your store
return new actions.SetAllItemsDetails(allItemsWithDetails);
})
);
I have provided pseudo code which will give you an idea of how to achieve what you want to do. For more info, you can visit the official site of ngrx - https://ngrx.io/guide/effects