I have this data from firestore and I wanted to retrieve it dynamically with a where() but this is the error I'm getting:
TypeError: vaccines is not a function
The user collection:
[![enter image description here][1]][1]
Below are the codes:
const Vaccine = () => {
const [vaccines, setVaccines] = useState([]);
useEffect(() => {
const unsubscribe = firestore
.collection("vaccines")
.onSnapshot((snapshot) => {
const arr = [];
snapshot.forEach((doc) =>
arr.push({
...doc.data(),
id: doc.id,
})
);
setVaccines(arr);
});
return () => {
unsubscribe();
};
}, []);
Preface
As highlighted in the comments on the original question, this query structure is not advised as it requires read access to sensitive user data under /users that includes private medical data.
DO NOT USE THIS CODE IN A PRODUCTION/COMMERICAL ENVIRONMENT. Failure to heed this warning will lead to someone suing you for breaches of privacy regulations.
It is only suitable for a school project (although I would a fail a student for such a security hole) or proof of concept using mocked data. The code included below is provided for education purposes, to solve your specific query and to show strategies of handling dynamic queries in React.
From a performance standpoint, in the worst case scenario (a cache miss), you will be billed one read, for every user with at least one dose of any vaccine, on every refresh, for every viewing user. Even though your code doesn't use the contents of any user document, your code must download all of this data too because the Client SDKs do not support the select() operator.
For better security and performance, perform this logic server-side (e.g. Cloud Function, a script on your own computer, etc) and save the results to a single document that can be reused by all users. This will allow you to properly tighten access to /users. It also significantly simplifies the code you need to display the graphs and live statistics on the client-side.
useEffect
As stated by the React documentation on the Rules of hooks:
Only Call Hooks at the Top Level
Don’t call Hooks inside loops, conditions, or nested functions. Instead, always use Hooks at the top level of your React function, before any early returns. By following this rule, you ensure that Hooks are called in the same order each time a component renders. That’s what allows React to correctly preserve the state of Hooks between multiple useState and useEffect calls.
The documentation further elaborates that React relies on the order in which Hooks are called, which means that you can't have hook definitions behind conditional logic where their order and quantity changes between renders. If your hooks rely on some conditional logic, it must be defined inside of the hook's declaration.
As an example, if you have an effect that relies on other data, with this logic:
const [userProfile, setUserProfile] = useState();
const [userPosts, setUserPosts] = useState(null);
useEffect(() => {
// get user profile data and store in userProfile
}, []);
if (userProfile) {
useEffect(() => {
// get user post list and store in userPosts
}, [userProfile]);
}
you need to instead use:
const [userProfile, setUserProfile] = useState();
const [userPosts, setUserPosts] = useState(null);
useEffect(() => {
// get user profile data and store in userProfile
}, []);
useEffect(() => {
if (!userProfile) {
// not ready yet/signed out
setUserPosts(null);
return;
}
// get user post list and store in userPosts
}, [userProfile]);
Similarly, for arrays:
someArray && someArray.forEach((entry) => {
useEffect(() => {
// do something with entry to define the effect
}, /* variable change hooks */);
});
should instead be:
useEffect(() => {
if (!someArray) {
// not ready yet
return;
}
const cleanupFunctions = [];
someArray.forEach((entry) => {
// do something with entry to define an effect
cleanupFunctions.push(() => {
// clean up the effect
});
});
// return function to cleanup the effects created here
return () => {
cleanupFunctions.forEach(cleanup => cleanup());
}
}, /* variable change hooks */);
Because this looks a lot like lifecycle management, you are actually better off replacing it with nested components rather than using hooks, like so:
return (
<> // tip: React.Fragment shorthand (used for multiple top-level elements)
{
someArray && someArray
.map(entry => {
return <Entry key={entry.key} data={entry.data} />
})
}
</>
);
Adapting to your code
Note: The code here doesn't use onSnapshot for the statistics because it would cause a rerender every time a new user is added to the database.
const getVaccineStats = (vaccineName) => {
const baseQuery = firestore
.collection("users")
.where("doses.selectedVaccine", "==", vaccine);
const oneDoseQueryPromise = baseQuery
.where("doses.dose1", "==", true)
.where("doses.dose2", "==", false)
.get()
.then(querySnapshot => querySnapshot.size);
const twoDoseQueryPromise = baseQuery
.where("doses.dose1", "==", true)
.where("doses.dose2", "==", true)
.get()
.then(querySnapshot => querySnapshot.size);
return Promise.all([oneDoseQueryPromise, twoDoseQueryPromise])
.then(([oneDoseCount, twoDoseCount]) => ({ // tip: used "destructuring syntax" instead of `results[0]` and `results[1]`
withOneDose: oneDoseCount,
withTwoDoses: twoDoseCount
}));
};
const Vaccine = () => {
const [vaccines, setVaccines] = useState();
const [vaccineStatsArr, setVaccineStatsArr] = useState([]);
// Purpose: Collect vaccine definitions and store in `vaccines`
useEffect(() => {
return firestore // tip: you can return the unsubscribe function from `onSnapshot` directly
.collection("vaccines")
.onSnapshot({ // tip: using the Observer-like syntax, allows you to handle errors
next: (querySnapshot) => {
const vaccineData = []; // tip: renamed `arr` to indicate what the data contains
querySnapshot.forEach((doc) =>
vaccineData.push({
...doc.data(),
id: doc.id,
});
);
setVaccines(vaccineData);
}),
error: (err) => {
// TODO: Handle database errors (e.g. no permission, no connection)
}
});
}, []);
// Purpose: For each vaccine definition, fetch relevant statistics
// and store in `vaccineStatsArr`
useEffect(() => {
if (!vaccines || vaccines.length === 0) {
return; // no definitions ready, exit early
}
const getVaccineStatsPromises = vaccines
.map(({ vaccine }) => [vaccine, getVaccineStats(vaccine)]);
// tip: used "destructuring syntax" on above line
// (same as `.map(vaccineInfo => [vaccineInfo.vaccine, getVaccineStats(vaccineInfo.vaccine)]);`)
let unsubscribed = false;
Promise.all(getVaccineStatsPromises)
.then(newVaccineStatsArr => {
if (unsubscribed) return; // unsubscribed? do nothing
setVaccineStatsArr(newVaccineStatsArr);
})
.catch(err => {
if (unsubscribed) return; // unsubscribed? do nothing
// TODO: handle errors
});
return () => unsubscribed = true;
}, [vaccines]);
if (!vaccines) // not ready? hide element
return null;
if (vaccines.length === 0) // no vaccines found? show error
return (<span class="error">No vaccines found in database</span>);
if (vaccineStatsArr.length === 0) // no stats yet? show loading message
return (<span>Loading statistics...</span>);
return (<> // tip: React.Fragment shorthand
{
vaccineStatsArr.map(([name, stats]) => {
// this is an example component, find something suitable
// the `key` property is required
return (<BarGraph
key={name}
title={`${name} Statistics`}
columns={["One Dose", "Two Doses"]}
data={[stats.withOneDose, stats.withTwoDoses]}
/>);
});
}
</>);
};
export default Vaccine;
Live Statistics
If you want your graphs to be updated live, you need "zip together" the two snapshot listeners into one, similar to the rxjs combineLatest operator. Here is an example implementation of this:
const onVaccineStatsSnapshot => (vaccine, observerOrSnapshotCallback, errorCallback = undefined) => {
const observer = typeof observerOrCallback === 'function'
? { next: observerOrSnapshotCallback, error: errorCallback }
: observerOrSnapshotCallback;
let latestWithOneDose,
latestWithTwoDoses,
oneDoseReady = false,
twoDosesReady = false;
const fireNext = () => {
// don't actually fire event until both counts have come in
if (oneDoseReady && twoDosesReady) {
observer.next({
withOneDose: latestWithOneDose,
withTwoDoses: latestWithTwoDoses
});
}
};
const fireError = observer.error || (err) => console.error(err);
const oneDoseUnsubscribe = baseQuery
.where("doses.dose1", "==", true)
.where("doses.dose2", "==", false)
.onSnapshot({
next: (querySnapshot) => {
latestWithOneDose = querySnapshot.size;
oneDoseReady = true;
fireNext();
},
error: fireError
});
const twoDoseUnsubscribe = baseQuery
.where("doses.dose1", "==", true)
.where("doses.dose2", "==", true)
.onSnapshot({
next: (querySnapshot) => {
latestWithTwoDoses = querySnapshot.size;
twoDosesReady = true;
fireNext();
},
error: fireError
});
return () => {
oneDoseUnsubscribe();
twoDoseUnsubscribe();
};
}
You could rewrite the above function to make use of useState, but this would unnecessarily cause components to rerender when they don't need to.
Usage (direct):
const unsubscribe = onVaccineStatsSnapshot(vaccineName, {
next: (statsSnapshot) => {
// do something with { withOneDose, withTwoDoses } object
},
error: (err) => {
// TODO: error handling
}
);
or
const unsubscribe = onVaccineStatsSnapshot(vaccineName, (statsSnapshot) => {
// do something with { withOneDose, withTwoDoses } object
});
Usage (as a component):
const VaccineStatsGraph = (vaccineName) => {
const [stats, setStats] = useState(null);
useEffect(() => onVaccineStatsSnapshot(vaccineName, {
next: (newStats) => setStats(newStats),
error: (err) => {
// TODO: Handle errors
}
}, [vaccineName]);
if (!stats)
return (<span>Loading graph for {vaccineName}...</span>);
return (
<BarGraph
title={`${name} Statistics`}
columns={["One Dose", "Two Doses"]}
data={[stats.withOneDose, stats.withTwoDoses]}
/>
);
}
vaccines is an array and not a function. You are trying to run a map on vaccines. Try refactoring your code to this:
vaccines &&
vaccines.map((v, index) => {
// ...
})
Also do check: How to call an async function inside a UseEffect() in React?
here is the code, that works for you:
function DatafromFB() {
const[users, setUsers] = useState({});
useEffect(()=>{
const fetchVaccine = async () => {
try {
const docs = await db.collection("vaccines").get();;
docs.forEach((doc) => {
doc.data().vaccineDetails
.forEach(vaccineData=>{
fetchUsers(vaccineData.vaccine)
})
})
} catch (error) {
console.log("error", error);
}
}
const fetchUsers = async (vaccine)=>{
try {
const docs = await db.collection("users")
.where("doses.selectedVaccine", "==", vaccine).get();
docs.forEach(doc=>{
console.log(doc.data())
setUsers(doc.data());
})
}catch(error){
console.log("error", error);
}
}
fetchVaccine();
},[])
return (
<div>
<h1>{users?.doses?.selectedVaccine}</h1>
</div>
)
}
export default DatafromFB
what is ${index.vaccine} I think it must be v.vaccine
also setSize(snap.size); will set set size commonly not vaccine specific
I'm trying to build a very simple app for searching articles and using the localstorage to display more info about each article but when I set to save into the session storage for some reason is saving the initial or previous state, I assume because I need to set async for this but I just can't figure how
This is how I have it right now, findArticleQuery() is called on the handleSubmit
useEffect(
() =>{
findArticlesQuery();
} ,[]
)
const findArticlesQuery = (query) => { //search function
axios.get(`url`)
.then(res => {
[res.data].map((val) =>(
setState(val)
))
}).catch(error => {
console.log(error.response)
});
}
const handleSubmit = (e) => {
e.preventDefault();
findArticlesQuery(e.target.search.value)
sessionStorage.setItem('localData', JSON.stringify(state)) //<--here I get the value of the previous state
e.target.search.value = '';
}
I need to use the session storage because I will have a detailed article component page.
Thank you guys!
You can get search result from findArticlesQuery() like below.
...
const findArticlesQuery = (query) => { //search function
return axios.get(`url`)
.then(res => {
setState(res.data)
return res.data
})
}
const handleSubmit = (e) => {
e.preventDefault();
findArticlesQuery(e.target.search.value)
.then(val => sessionStorage.setItem('localData', JSON.stringify(val)))
e.target.search.value = '';
}
For saving state in the localStorage with React Hooks, something I've been using and that is extremely convenient is useLocalStorage.
Disclaimer : I am not the creator of this lib.
I'm trying to implement a custom hook to provide the app with a guest shopping cart. My hook wraps around the useMutation hook from Apollo and it saves the shopping cart id in a cookie while also providing a function to "reset" the cart (basically, to remove the cookie when the order is placed).
Code time! (some code omitted for brevity):
export const useGuestCart = () => {
let cartId;
const [createCart, { data, error, loading }] = useMutation(MUTATION_CREATE_CART);
console.log(`Hook!`);
if (!cartId || cartId.length === 0) {
createCart();
}
if (loading) {
console.log(`Still loading`);
}
if (data) {
console.log(`Got cart id ${data.createEmptyCart}`);
cartId = data.createEmptyCart;
}
const resetGuestCart = useCallback(() => {
// function body here
});
return [cartId, resetGuestCart];
};
In my component I just get the id of the cart using let [cartId, resetCart] = useGuestCart(); .
When I run my unit test (using the Apollo to provide a mock mutation) I see the hooked invoked several times, with an output that looks something like this:
console.log src/utils/hooks.js:53
Hook!
console.log src/utils/hooks.js:53
Hook!
console.log src/utils/hooks.js:59
Still loading
console.log src/utils/hooks.js:53
Hook!
console.log src/utils/hooks.js:62
Got cart id guest123
console.log src/utils/hooks.js:53
Hook!
console.log src/utils/hooks.js:53
Hook!
I'm only getting started with hooks, so I'm still having trouble grasping the way they work. Why so many invocations of the hook?
Thank you for your replies!
Think of hooks as having that same code directly in the component. This means that every time the component renders the hook will run.
For example you define:
let cartId;
// ...
if (!cartId || cartId.length === 0) {
createCart();
}
The content inside the statement will run on every render as cartId is created every time and it doesn't have any value assigned at that point. Instead of using if statements use useEffect:
export const useGuestCart = () => {
const [cartId, setCartId] = useState(0);
const [createCart, { data, error, loading }] = useMutation(
MUTATION_CREATE_CART
);
const resetGuestCart = () => {
// function body here
};
useEffect(() => {
if(!cartId || cartId.length === 0){
createCart();
}
}, [cartId]);
useEffect(() => {
// Here we need to consider the first render.
if (loading) {
console.log(`Started loading`);
} else {
console.log(`Finished loading`);
}
}, [loading]);
useEffect(() => {
// Here we need to consider the first render.
console.log(`Got cart id ${data.createEmptyCart}`);
setCartId(data.createEmptyCart);
}, [data]);
return [cartId, resetGuestCart];
};
Also notice that there is no actual benefit from using useCallback if the component which is receiving the function is not memoized.
I am currently building a small web app with Firebase and React, but I am having trouble fetching for specific items in the Firebase from the React client-side.
That being said, I'm used to javascript, where a simple fetch might look something like:
const url = 'www.example.com/api/'
const id = '123'
fetch(url + id) <---specific
.then(res => res.json())
.then(result => this.setState({results: result})
.catch(err => console.log(err))
However, I haven't been able to find any documentation on something that looks similar with firebase.
A more specific issue below:
class StoryItem extends Component {
constructor(props) {
super(props);
this.state = {
story: this.props.location.myCustomProps
};
}
componentDidMount() {
//this should do a fetch request based on the
//params id to get the specific item in the firebase
//right now it is being passed as prop which is unreliable because when page refresh state is reset
//user should be able to access content
//without having to go to previous page
console.log(this.state.story)
}
One way I've tried to get the specific object from the firebase is this:
componentDidMount(props) {
const ref = firebase.database().ref("items");
ref.on("value", snapshot => {
let storiesObj = snapshot.val();
storiesObj
.child(this.props.match.params.id)
.then(() => ref.once("value"))
.then(snapshot => snapshot.val())
.catch(error => ({
errorCode: error.code,
errorMessage: error.message
}));
});
}
In this case, the error is
Any help would be appreciated, also, if anyone knows of any good documentation on firebase, feel free to send me a link.
Thank you
The trick is, you don't have to get the value of all items first, as you do.
You should locate the items ref, then lookup a child that you want and get the value of that child with .on or .once.
Something like that, based on your example code:
componentDidMount() {
firebase.database().ref("items");
.child(this.props.match.params.id)
.once("value")
.then(snapshot => snapshot.val())
.catch(error => ({
errorCode: error.code,
errorMessage: error.message
}));
}
For better understanding, let's take a look at the original code and try to figure out why it errors out:
componentDidMount(props) {
// ⬇️ this ref points to ALL items
const ref = firebase.database().ref("items");
// ⬇️ here we're asking for the value stored under the above ref
ref.on("value", snapshot => {
let storiesObj = snapshot.val();
/* so firebase gives us what we ask for, storiesObj
* is probably a huge js object with all the items inside.
* And since it's just a regular js object,
* it does not have a `child` method on it, thus calling .child errors out.
*/
storiesObj
.child(this.props.match.params.id)
.then(() => ref.once("value"))
.then(snapshot => snapshot.val())
.catch(error => ({
errorCode: error.code,
errorMessage: error.message
}));
});
}
I want to load a bunch of data that involves multiple APIs, I did setState in foreach, it worked but I think the design is wrong, as I see flickering on my screen.
API.fetchMain().then(main => {
main.forEach(o => {
const main_id = o.main_id
this.setState({
main: o
})
API.fetchSub(main_id)
.then(sub => {
this.setState({
sub
})
API.fetchOthers(main_id, sub.id)
.then(others => {
this.setState({
others
})
})
})
})
}
I think I should use promises to refactor, I tried but I think my design was wrong.
API.fetchMain().then(main => {
let promise = []
main.forEach(o => {
const main_id = o.main_id
this.setState({
main: o
})
promise.push(
API.fetchSub(main_id)
.then(sub => {
return API.fetchOthers(main_id, sub.id)
})
)
})
Promise.all(promise).then(resp => console.log('do setState here'))
}
Need help.
It looks to me that you are fetching a resource that provides you with information about how to make further requests. If you are open to using a fetch library I would recommend axios. Heres how I would envision it looking
import axios from 'axios'
fetch(){
// Make the initial request
var options = { url: "URL of main resource", method: "GET" }
axios(options).then(res => {
// Create an array of next requests from the response
var next_requests = res.data.main.map(id => axios.get(`${resource_url}/${id}`))
//Make the requests in parallel
axios.all(next_requests).then(axios.spread(() => {
//since we don't know how many request we can iterate
//over the arguments object and build the new state
var newState = {}
arguments.forEach(i => {
// how you want to structure the the state before setting it
})
this.setState(newState)
})
}).catch(err => //error handling logic here)
}
From my understanding of your question you could also (since you are using react) break your fetch request into components that get called when they mount. A quick example:
const class MainComp extends Component {
constructor(props){
super(props)
this.state = {
main: []
}
}
componentDidMount(){ this.fetchMain() }
fetchMain() {
axios.get('url').then(res =>
this.setState({main_id: res.data.main.id})
}
sendSubFetchToParent(dataFromChild){
// Do what you need to with the data from the SubComp child
}
render(){
return (
{this.state.main.map(id => <SubComp id={id) afterFetch={this.sendSubFetchToParent}/>}
)
}
}
const class SubComp extends Component {
componentDidMount(){ this.fetchSub() }
fetchSub() {
//Pass the results to the parent after the fetch completes.
// You can add the usual error handling here as well.
axios.get('url').then(res => this.props.afterFetch(res.data))
}
render(){
//Return null or render another sub component for further nested requests
return null
}
}
In the above, MainComp initiates a request. When it gets a response (which in your example is an array) we set that response to the state. This triggers rerender which will mount n number of SubComp. When those mount they will initiate their requests to get data. For SubComp we pass a callback from the parent so SubComp can send its fetch response back to MainComp (And handle it appropriately by setting state etc etc). You can return null in SubComp or have it mount a component that will make further request.
In that way your fetch requests are now componentized.