Angular subscribe elegant
I'd like to ask about my subscribe method. I want to get my objects(employees) from firebase and do a loot of operations on my objects, like avg salaries, avg missed days... In my opinion it looks so horrible. My service void:
getEmployees(): Observable<Employee[]> {
return this.db.list<Employee>(this.Api_url).snapshotChanges()
.pipe(map(response => response.map(car => this.assignKey(car))));
}
And my ngOnInit:
ngOnInit() {
this.subscribtion = this.mainservice.getEmployees().subscribe((emps)=> {
this.employees = emps;
this.workersdatas = [];
this.educationdatas = [];
this.checkavaragesalaries(emps);
this.countMonthAbsences(emps, 1);
this.countMonthSalaries(emps, 1);
this.departments.forEach((one)=> {
const dep = emps.filter(on => on.department.includes(one) && this.FilterEmployees(on)).length;
this.workersdatas.push({name: one, value: dep});
});
this.educations.forEach((one)=> {
const edu = emps.filter(on => on.education.includes(one)).length;
this.educationdatas.push({name: one, value: edu});
});
const mynumb =this.educationdatas.map(on => on.value);
this.mosteducation = this.educationdatas.filter(one => one.value === Math.max(...mynumb))[0].name;
}); }
Should I unsubscribe() it on ngOnDestroy or that's not necessary? Is that allowed to write it like that?
My favourite unsubscribe pattern is to use takeUntil
. takeUntil()
accepts an observable, and will stop the subscription when that observable emits a value.
The long-winded way to do this is emit a value in ngOnDestroy()
.
destroyed = new Subject<void>();
ngOnInit(): void {
myService.getData().pipe(
takeUntil(this.destroyed)
).subscribe(data => {
// process data
});
}
ngOnDestroy(): void {
this.destroyed.next();
this.destroyed.complete();
}
This gets quite tedious once you've done this a few times. The best solution I've seen for this (and currently use) is to set up a shared function that emits the destroyed value for you. Source Credit
import { OnDestroy } from '@angular/core';
import { ReplaySubject, Subject, Observable } from 'rxjs';
export function componentDestroyed(component: OnDestroy): Observable<void> {
const oldNgOnDestroy: () => void = component.ngOnDestroy;
const destroyed: Subject<void> = new ReplaySubject<void>(1);
component.ngOnDestroy = () => {
oldNgOnDestroy.apply(component);
destroyed.next(undefined);
destroyed.complete();
};
return destroyed.asObservable();
}
It is then almost trivial to use in your component:
ngOnInit(): void {
myService.getData().pipe(
takeUntil(componentDestroyed(this))
).subscribe(data => {
// process data
});
}
ngOnDestroy(): void {}
All you have to do is implement ngOnDestroy in your component and add takeUntil(componentDestroyed(this))
to your pipe.