In my project there are activities that people have created, joined, bookmarked or organized. I've read a lot of these question already. But most of the code was less complex or people forgot to subscribe...
I would like to get all the activities in a certain time period and then add creator information (name, image, etc) and add booleans if the user retrieving these activities has joined/bookmarked/organized this activity. The code I used before would provide live updates (ex. I join an activity, by adding my userId to the participants array and the activity.joined would update to true).
Previous code:
public getActivities(user: UserProfileModel): Observable<Array<ActivityModel>> {
const now: number = moment().startOf('day').unix();
const later: number = moment().startOf('day').add(30, 'day').unix();
return this.afs.collection<ActivityModel>(`cities/${user.city.id}/activities`, ref => ref
.where('datetime', '>=', now)
.where('datetime', '<=', later))
.valueChanges({ idField: 'id' })
.pipe(
map(activities => activities.map(activity => {
const bookmarked = activity.bookmarkers ? activity.bookmarkers.includes(user.uid) : false;
const joined = activity.participants ? activity.participants.includes(user.uid) : false;
const organized = activity.organizers ? activity.organizers.includes(user.uid) : false;
return { bookmarked, joined, organized, ...activity } as ActivityModel;
}))
);
}
The I wanted to add the creator as an observable object, so their latest changes in name or profile picture would be shown. But with this code change, my getActivities doesn't emit any updates anymore...
My new code:
public getActivities(user: UserProfileModel): Observable<Array<CombinedActivityCreatorModel>> {
const now: number = moment().startOf('day').unix();
const later: number = moment().startOf('day').add(30, 'day').unix();
return this.afs.collection<ActivityModel>(`cities/${user.city.id}/activities`, ref => ref
.where('datetime', '>=', now)
.where('datetime', '<=', later))
.valueChanges({ idField: 'id' })
.pipe(
concatMap(activities => {
const completeActivityData = activities.map(activity => {
const activityCreator: Observable<UserProfileModel> = this.getCreator(activity.creator);
const bookmarked = activity.bookmarkers ? activity.bookmarkers.includes(user.uid) : false;
const joined = activity.participants ? activity.participants.includes(user.uid) : false;
const organized = activity.organizers ? activity.organizers.includes(user.uid) : false;
return combineLatest([
of({ bookmarked, joined, organized, ...activity }),
activityCreator
]).pipe(
map(([activityData, creatorObject]: [ActivityModel, UserProfileModel]) => {
return {
...activityData,
creatorObject: creatorObject
} as CombinedActivityCreatorModel;
})
);
});
return combineLatest(completeActivityData);
})
);
}
The code has become a bit complex, that I don't see the solution myself. Anybody that can offer some assistance?
Looks like one of activityCreator doesn't emit a value, combineLatest requires all observables to emit at least once.
I would recommend you to debug how activityCreator behaves.
If it's fine that it doesn't emit you have 2 options: startWith to set a value for an initial emit, or defaultIfEmpty, it emits in case if stream is going to be closed without any emit.
activityCreator = this.getCreator(activity.creator).pipe(
// startWith(null), // for example if you want to trigger combineLatest.
// defaultIfEmpty(null), // in case of an empty stream.
);
another thing is concatMap it requires an observable to complete, only then it switches to the next one, parhaps mergeMap or switchMap fits here better.
Try the code below and add its output to the comments. Thanks.
const activityCreator: Observable<UserProfileModel> = this.getCreator(activity.creator).pipe(
tap(
() => console.log('getCreator:emit'),
() => console.log('getCreator:error'),
() => console.log('getCreator:completed'),
),
);
Related
I use the following method in odder to retrieve data by passing pageIndex (1) and pageSize (500) for each HTTP call.
this.demoService.geList(1, 500).subscribe(data => {
this.data = data.items;
});
The response has a property called isMore and I want to modify my method in odder to continue HTTP calls if isMore is true. I also need to merge the returned values and finally return the accumulated values.
For example, assuming that there are 5000 records and until 10th HTTP call, the service returns true for isMore value. After 10th HTTP call, it returns false and then this method sets this.data value with the merged 5000 records. For this problem, should I use mergeMap or expand or another RxJs operator? What is the proper way to solve this problem?
Update: I use the following approach, but it does not merge the returned values and not increase the pageIndex. For this reason it does not work (I tried to make some changes, but could not make it work).
let pageIndex = 0;
this.demoService.geList(pageIndex+1, 500).pipe(
expand((data) => {
if(data.isComplete) {
return of(EMPTY);
} else {
return this.demoService.geList(pageIndex+1, 500);
}
})
).subscribe((data) => {
//your logic here
});
Update II:
of({
isMore : true,
pageIndex: 0,
items: []
}).pipe(
expand(data => demoService.geList(data.pageIndex+1, 100)
.pipe(
map(newData => ({...newData, pageIndex: data.pageIndex+1}))
)),
// takeWhile(data => data.isMore), //when using this, it does not work if the total record is less than 100
takeWhile(data => (data.isMore || data.pageIndex === 1)), // when using this, it causing +1 extra HTTP call unnecessarily
map(data => data.items),
reduce((acc, items) => ([...acc, ...items]))
)
.subscribe(data => {
this.data = data;
});
Update III:
Finally I made it work by modifying Elisseo's approach as shown below. Howeveri **I need to make it void and set this.data parameter in this getData() method. How can I do this?
getData(pageIndex, pageSize) {
return this.demoService.geList(pageIndex, pageSize).pipe(
switchMap((data: any) => {
if (data.isMore) {
return this.getData(pageIndex+1, pageSize).pipe(
map((res: any) => ({ items: [...data.items, ...res.items] }))
);
}
return of(data);
})
);
}
I want to merge the following subscribe part to this approach but I cannot due to some errors e.g. "Property 'pipe' does not exist on type 'void'."
.subscribe((res: any) => {
this.data = res;
});
getData(pageIndex, pageSize) {
return this.demoService.getList(pageIndex, pageSize).pipe(
switchMap((data: any) => {
if (!data.isCompleted) {
return this.getData(pageIndex+1, pageSize).pipe(
map((res: any) => ({ data: [...data.data, ...res.data] }))
);
}
return of(data);
})
);
}
stackblitz
NOTE: I updated pasing as argument pageIndex+1 as #mbojko suggest -before I wrote pageIndex++
UPDATE 2
Using expand operator we need take account that we need feed the "recursive function" with an object with pageIndex -it's necesarry in our call- for this, when we make this.demoService.getList(data.pageIndex+1,10) we need "transform the result" adding a new property "pageIndex". for this we use "map"
getData() {
//see that initial we create "on fly" an object with properties: pageIndex,data and isCompleted
return of({
pageIndex:1,
data:[],
isCompleted:false
}).pipe(
expand((data: any) => {
return this.demoService.getList(data.pageIndex,10).pipe(
//here we use map to create "on fly" and object
map((x:any)=>({
pageIndex:data.pageIndex+1, //<--pageIndex the pageIndex +1
data:[...data.data,...x.data], //<--we concatenate the data using spread operator
isCompleted:x.isCompleted})) //<--isCompleted the value
)
}),
takeWhile((data: any) => !data.isCompleted,true), //<--a take while
//IMPORTANT, use "true" to take account the last call also
map(res=>res.data) //finally is we only want the "data"
//we use map to return only this property
)
}
Well we can do a function like this:
getData() {
of({pageIndex:1,data:[],isCompleted:false}).pipe(
expand((data: any) => {
return this.demoService.getList(data.pageIndex,10).pipe(
tap(x=>{console.log(x)}),
map((x:any)=>({
pageIndex:data.pageIndex+1,
data:[...data.data,...x.data],
isComplete:x.isComplete}))
)
}),
takeWhile((data: any) => !data.isComplete,true), //<--don't forget the ",true"
).subscribe(res=>{
this.data=res.data
})
}
See that in this case we don't return else simple subscribe to the function and equal a variable this.data to res.data -it's the reason we don't need the last map
Update 3 by Mrk Sef
Finally, if you don't want your stream to emit intermittent values and you just want the final concatenated data, you can remove the data concatenation from expand, and use reduce afterward instead.
getData() {
of({
pageIndex: 1,
data: [],
isCompleted: false
})
.pipe(
expand((prevResponse: any) => this.demoService.getList(prevResponse.pageIndex, 10).pipe(
map((nextResponse: any) => ({
...nextResponse,
pageIndex: prevResponse.pageIndex + 1
}))
)
),
takeWhile((response: any) => !response.isCompleted, true),
// Keep concatenting each new array (data.items) until the stream
// completes, then emit them all at once
reduce((acc: any, data: any) => {
return [...acc, ...data.data];
}, [])
)
.subscribe(items => {
this.data=items;
});
}
It doesn't matter if you're total record change as long as api response give you the isMore flag.
I'm skipping the part how to implement reducer action event i'm assuming you've already done that part. So i will just try to explain with pseudo codes.
You have a table or something like that with pagination data. on intial state you can just create an loadModule effect or using this fn:
getPaginationDataWithPageIndex(pageIndex = 1){
this.store.dispatch(new GetPaginationData({ pageIndex: pageIndex, dataSize: 500}));
}
in your GetPaginationData effect
... map(action => {
return apicall.pipe(map((response)=> {
if(response.isMore){
return new updateState({data:response.data, isMore: responseisMore})
} else {
return new updateState({isMore: response.isMore}),
}
}})
`
all you have to left is subscribing store in your .ts if isMore is false you will not display the next page button. and on your nextButton or prevButton's click method you should have to just dispatch the action with pageIndex
I do not think recursion is the correct approach here:
interval(0).pipe(
map(count => this.demoService.getList(count + 1, 500)),
takeWhile(reponse => response.isMore, true),
reduce((acc, curr) => //reduce any way you like),
).subscribe();
This should make calls to your endpoint until the endpoint returns isMore === false. The beautiful thing about interval is that we get the count variable for free.
But if you are set on using recrsion, here is the rxjs-way to do that using the expand-operator (see the docs). I find it slightly less readable, as it requires an if-else-construct which increases code complexity. Also the outer 'counter' variable just isn't optimal.
let index = 1;
this.demoService.geList(index, 500).pipe(
expand(response => response.isMore ? this.demoService.geList(++index, 500) : empty()),
reduce((acc, curr) => //reduce here)
).subscribe();
I have two services named 'PatientsService' and 'AppointmentService'. In third service 'AppointedPatientsService', I want to subscribe to AppointmentService to get all booked appointments with patientId and after that I want to repeatedly subscribe to PatientsService.getPatient(patientId) to get Patient's data with patientId. And then, I want to return new array named allAppointedPatients which holds all appointments with patient's data. I tried this...
getAppointments() {
let allAppointments: Appointment[] = [];
const allAppointedPatients: AppointedPatient[] = [];
return this.appointmentService.fetchAllAppointments().pipe(
take(1),
tap(appointments => {
allAppointments = appointments;
for (const appointment of allAppointments) {
this.patientsService.getPatient(appointment.patientId).pipe(
tap(patient => {
const newAppointment = new AppointedPatient(patient.firstName,
patient.lastName,
patient.address,
patient.casePaperNumber,
appointment.appointmentDateTime);
allAppointedPatients.push(newAppointment);
})
).subscribe();
}
return allAppointedPatients;
}),
pipe(tap((data) => {
return this.allAppointedPatients;
}))
);
}
This is not working and I know there must be better way to handle such scenario. Please help...
You are messing up the async code (observables) with sync code by trying to return the allAppointedPatients array synchronously.
Understand first how async code is working in Javascript and also why Observables (streams) are so useful.
Try the code below and make sure you understand. Of course, I was not able to test it so make your own changes if needed.
getAppointments(): Observable<AppointedPatient[]> {
return this.appointmentService.fetchAllAppointments()
.pipe(
switchMap(appointments => {
const pacientAppointments = [];
for (const appointment of allAppointments) {
// Extract the data aggregation outside or create custom operator
const pacientApp$ = this.patientsService.getPatient(appointment.patientId)
.pipe(
switchMap((pacient) => of(
new AppointedPatient(
patient.firstName,
patient.lastName,
patient.address,
patient.casePaperNumber,
appointment.appointmentDateTime
)
))
)
pacientAppoinments.push(pacientApp$);
}
return forkJoin(pacientAppointments);
});
}
You can use forkJoin:
forkJoin(
getSingleValueObservable(),
getDelayedValueObservable()
// getMultiValueObservable(), forkJoin on works for observables that complete
).pipe(
map(([first, second]) => {
// forkJoin returns an array of values, here we map those values to an object
return { first, second };
})
);
I'm calling an API and receiving an array of results, I'm checking for pagination and if more pages exist I call the next page, repeat until no more pages.
For each array of results, I call another endpoint and do the exact same thing: I receive an array of results, check for another page and call endpoint again. Wash, rinse repeat.
For instance:
I want to grab a list of countries that might be a paginated response, then for each country I want to grab a list of cities, which might also be paginated. And for each city I execute a set of transformations and then store in a database.
I already tried this, but got stuck:
const grabCountries = Observable.create(async (observer) => {
const url = 'http://api.com/countries'
let cursor = url
do {
const results = fetch(cursor)
// results = {
// data: [ 'Canada', 'France', 'Spain' ],
// next: '47asd8f76358df8f4058898fd8fab'
// }
results.data.forEach(country => { observer.next(country) })
cursor = results.next ? `${url}/${results.next}` : undefined
} while(cursor)
})
const getCities = {
next: (country) => {
const url = 'http://api.com/cities'
let cursor = url
do {
const results = fetch(cursor)
// results = {
// data: [
// 'Montreal', 'Toronto',
// 'Paris', 'Marseilles',
// 'Barcelona', 'Madrid'
// ],
// next: '89ghjg98nd8g8sdfg98gs9h868hfoig'
// }
results.data.forEach(city => {
`**** What do I do here?? ****`
})
cursor = results.next ? `${url}/${results.next}` : undefined
} while(cursor)
}
}
I tried a few approaches:
Making a subject (sometimes I'll need to do parallel processed base on the results of 'grabCountries'. For example I may want to store the countries in a DB in parallel with grabbing the Cities.)
const intermediateSubject = new Subject()
intermediateSubject.subscribe(storeCountriesInDatabase)
intermediateSubject.subscribe(getCities)
I also tried piping and mapping, but it seems like it's basically the same thing.
As I was writing this I thought of this solution and it seems to be working fine, I would just like to know if I'm making this too complicated. There might be cases where I need to make more that just a few API calls in a row. (Imagine, Countries => States => Cities => Bakeries => Reviews => Comments => Replies) So this weird mapping over another observer callback pattern might get nasty.
So this is what I have now basically:
// grabCountries stays the same as above, but the rest is as follows:
const grabCities = (country) =>
Observable.create(async (observer) => {
const url = `http://api.com/${country}/cities`
let cursor = url
do {
const results = fetch(cursor)
// results = {
// data: [
// 'Montreal', 'Toronto',
// 'Paris', 'Marseilles',
// 'Barcelona', 'Madrid'
// ],
// next: '89ghjg98nd8g8sdfg98gs9h868hfoig'
// }
results.data.forEach(city => {
observer.next(city)
})
cursor = results.next ? `${url}/${results.next}` : undefined
} while (cursor)
})
const multiCaster = new Subject()
grabCountries.subscribe(multiCaster)
multiCaster.pipe(map((country) => {
grabCities(country).pipe(map(saveCityToDB)).subscribe()
})).subscribe()
multiCaster.pipe(map(saveCountryToDB)).subscribe()
tl;dr - I call an API that receives a paginated set of results in an array and I need to map through each item and call another api that receives another paginated set of results, each set also in an array.
Is nesting one observable inside another and mapping through the results via 'callApiForCountries.pipe(map(forEachCountryCallApiForCities))' the best method or do you have any other recommendations?
Here's the code that should work with sequential crawling of next url.
You start with a {next:url} until res.next is not available.
of({next:http://api.com/cities}).pipe(
expand(res=>results.next ? `${url}/${results.next}` : undefined
takeWhile(res=>res.next!==undefined)
).subscribe()
OK, so I have spent a lot of brain power on this and have come up with two solutions that seem to be working.
const nestedFlow = () => {
fetchAccountIDs.pipe(map(accountIds => {
getAccountPostIDs(accountIds) // Has the do loop for paging inside
.pipe(
map(fetchPostDetails),
map(mapToDBFormat),
map(storeInDB)
).subscribe()
})).subscribe()
}
const expandedflow = () => {
fetchAccountIDs.subscribe((accountId) => {
// accountId { accountId: '345367geg55sy'}
getAccountPostIDs(accountId).pipe(
expand((results) => {
/*
results : {
postIDs: [
131424234,
247345345,
],
cursor: '374fg8v0ggfgt94',
}
*/
const { postIDs, cursor } = results
if (cursor) return getAccountPostIDs({...accountId, cursor})
return { postIDs, cursor }
}),
takeWhile(hasCursor, true), // recurs until cursor is undefined
concatMap(data => data.postIDs),
map(data => ({ post_id: data })),
map(fetchPostDetails),
map(mapToDBFormat),
map(storeInDB)
).subscribe()
})
}
Both seem to be working with similar performance. I read some where that leaving the data flow is a bad practice and you should pipe everything, but I don't know how to eliminate the first exit in the 'expandedFlow' because the 'expand' needs to call back an observable, but maybe it can be done.
Now I just have to solve the race condition issues from the time the 'complete' is called in getAccountPostIDs the the last record is stored in the DB. Currently in my test, the observer.complete is finishing before 3 of the upsert actions.
Any comments are appreciated and I hope this helps someone out in the future.
What you need is the expand operator. It behaves recursively so it fits the idea of having paginated results.
I'm trying to subscribe to an inner Observable. Here is what I'm doing:
getDates() {
if (this.booking.id) {
this.jobService.findById(this.booking.id)
.map(job => job[0])
.switchMap((job) => {
return job ? this.bookingService.findByPropertyId(job.property.id) : Observable.empty();
}, (job: Job, bookings: Booking[]) => {
this.mark_jobs_unavailable(job, bookings);
return job;
})
.subscribe(job => {
this.bookingJob = job;
});
}
}
My code is working fine, The only thing I'm trying to achieve is to subscribe to changes of my Bookings as well. Currently as I'm not sure where should I subscribe to the Observable that I get from bookingService.findByPropertyId, My app does not reflect to changes happening in bookings collection.
To get changes for Bookings, bookingService.findByProperyId() must return observable values whenever (i.e. it can return multiple values over a period of time) a change happens.
You can try something like this:
this.jobService.findById(this.booking.id)
.mergeAll() // or .mergeAll().first()
.switchMap(
job => this.bookingService.findByPropertyId(job.property.id),
(job, bookings) => [job, bookings]
)
.subscribe(([job, bookings]) => {
this.bookingJob = job;
this.mark_jobs_unavailable(job, bookings);
});
Now you have both job and bookings in the subscribe method
My question is a continuation of this excellent question and answer concerning the shape of paginated data in a redux store. I am using ngrx/store in an angular 2 app.
{
entities: {
users: {
1: { id: 1, name: 'Dan' },
42: { id: 42, name: 'Mary' }
}
},
visibleUsers: {
ids: [1, 42],
isFetching: false,
offset: 0
}
}
Based on the above shape I believe if the offset (or page, sort, etc.) from an incoming request payload changed then the visible users would change as well as the user entities by calling the DB. I have some actions and reducer functions to handle this and it works as expected. If the offset remains the same and the user is returning to the page the way they left it then the user entities should be returned by the store not the DB.
Where I am struggling is where to put that logic and which rxjs operators to use (still learning this).
I think the correct place is an effect. Here is what I have now in my angular2 app (I am injecting Actions, Store, and my UserService) that pulls new data every time the page is loaded.
#Effect loadUsers$ = this.actions$
.ofType('LOAD_USERS')
.switchMap(() => this.userService.query()
.map((results) => {
return new LoadUsersSuccessAction(results);
}))
.catch(() => Observable.of(new LoadUsersFailureAction()));
My best idea is something like this:
#Effect loadUsers$ = this.actions$
.ofType('LOAD_USERS')
.withLatestFrom(this.store.select(state => state.visibleUsers.offset))
.switchMap(([action, state]) => {
//something that looks like this??
//this syntax is wrong and I can't figure out how to access the action payload
state.offset === payload.offset
? this.store.select(state => state.entities.users)
: this.userService.query()
}
.map((results) => {
return new LoadUsersSuccessAction(results);
}))
.catch(() => Observable.of(new LoadUsersFailureAction()));
Not sure how to make this work. Thanks ahead.
I don't like answering my own questions but it took me quite a while to find the answer to this. I won't accept this answer as I am not sure this is the best way to go about things (still learning the ins/outs). It does however, work perfectly.
I found the correct syntax in a github gist. This code does not match my example but it clearly demonstrates "2 options for conditional ngrx effects" by either returning a store or api observable using some sort of condition.
Hope this helps someone.
Here it is:
#Effect()
selectAndLoadStore$: Observable<Action> = this.actions$
.ofType(storeActions.SELECT_AND_LOAD_STORE)
.withLatestFrom(this.store.select(ngrx.storeState))
.map(([action, storeState]) => [action.payload, storeState])
.switchMap(([storeName, storeState]) => {
const existsInStore = Boolean(storeState.urlNameMap[storeName]);
return Observable.if(
() => existsInStore,
Observable.of(new storeActions.SetSelectedStore(storeName)),
this.storeService.getByUrlName(storeName)
.map(store => new storeActions.LoadSelectedStoreSuccess(store))
);
});
#Effect()
selectAndLoadStore$: Observable<Action> = this.actions$
.ofType(storeActions.SELECT_AND_LOAD_STORE)
.withLatestFrom(this.store.select(ngrx.storeState))
.map(([action, storeState]) => [action.payload, storeState])
.switchMap(([storeName, storeState]) => {
const existsInStore = Boolean(storeState.urlNameMap[storeName]);
let obs;
if (existsInStore) {
obs = Observable.of(new storeActions.SetSelectedStore(storeName));
} else {
obs = this.storeService.getByUrlName(storeName)
.map(store => new storeActions.LoadSelectedStoreSuccess(store));
}
return obs;
});