How to manage downloading data in ionic 2 - download

Question

I have small issue with managing the downloading data of firebase to my ionic application.
For example: In the normal case [such as below code], the downloading data is normal [such as this image]
constructor(...){
this.questionsList = this.afd.list('/questions/');
}
But if I used "setInterval" [such as below code], the downloading of data increase [such as this image]
constructor(...){
this.questionsList = this.afd.list('/questions/');
this.favoritesList = this.afd.list('/favorites/',{
query:{
orderByChild:'user_id',
equalTo: userService.id,
}
})
this.joinObjects();
this.refreshIntervalId=setInterval(()=>{
this.joinObjects();
},250);
}
joinObjects(){
let TempListX=[];
this.favoritesList.take(1).subscribe(data1=>{
this.questionsList.take(1).subscribe(data2=>{
TempListX = data1.slice(0);
for(let i=0; i<data1.length; i++){
for(let j=0; j<data2.length; j++){
if(data1[i].question_id==data2[j].$key){
TempListX[i].qTitle=data2[j].title;
}
}
}
if (JSON.stringify(TempListX)===JSON.stringify(this.TempFavoritesList)) {
}else{
this.TempFavoritesList=TempListX.slice();
}
})
})
}
So is there any way to make the downloading data be such as normal case ?

Answer 1

As requested here is a refactored version of your code. I have to say I did not test it but it should outline the concept. The method joinObjects() is called every time an updated value/list arrives and not in a fixed interval which creates a lot of overhead. Notice the new instance variables I added and that I renamed your observables to favoritesList$ and questionsList$ (the dollar suffix is good practice to indicate that it is an observable (not a subscription, value, ...).
public questions;
public favorites;
constructor(...) {
this.questionsList$ = this.afd.list('/questions/');
this.favoritesList$ = this.afd.list('/favorites/', {
query: {
orderByChild: 'user_id',
equalTo: userService.id,
},
});
this.questionsList$.subscribe(updatedList => {
this.questions = updatedList;
this.joinObjects();
});
this.favoritesList$.subscribe(updatedList => {
this.favorites = updatedList;
this.joinObjects();
});
}
joinObjects() {
let TempListX = [];
TempListX = this.questions.slice(0);
for (let i = 0; i < this.questions.length; i++) {
for (let j = 0; j < this.favorites.length; j++) {
if (this.questions[i].question_id == this.favorites[j].$key) {
TempListX[i].qTitle = this.favorites[j].title;
}
}
}
if (JSON.stringify(TempListX) === JSON.stringify(this.TempFavoritesList)) {
} else {
this.TempFavoritesList = TempListX.slice();
}
}
I hope this brings you closer to your goal!