Exploring Improved Methods for Implementing Nested Subscriptions in Typescript

Question

Exploring Improved Methods for Implementing Nested Subscriptions in Typescript

In my Typescript code for Angular 11, I am working with two observables. The first one, getSelfPurchases(), returns data objects containing information like id, user_id, script_id, and pp_id. On the other hand, the second observable, getScriptDetails(32), provides details such as the script's name, author, and price.

My current implementation involves looping through the results of the first observable, making a call to the second observable for each item, and appending the retrieved script name to the original object. While this approach works, I believe it may not be the most efficient or elegant solution.

I have been exploring RXJS functionalities like switch map to optimize my code. However, I'm uncertain if using switch map would improve the performance significantly or if there are better alternatives. I would appreciate any insights or suggestions on how to refine this process.

this.userService.getSelfPurchases().subscribe(response => { // first observable
  this.purchases = response;

  this.purchases.forEach((purchase, index) => { // loop through our results
    this.scriptService.getScriptDetails(purchase.script_id).subscribe(responseTwo => { // second observable
      if (responseTwo[0] && responseTwo[0].sname !== undefined) {
        this.purchases[index].sname = responseTwo[0].sname; // append to our original purchases object
      }
    });
  });
});

angular typescript http rxjs observable

Answer 1

Answer №1

It is generally advised not to nest subscriptions for the sake of maintainability, extendibility, and readability. Nesting subscriptions can easily lead to callback hell, causing confusion and complexity in the code.

Instead of nesting subscriptions, you can refactor your code by mapping an array of purchases into an array of getScriptDetails calls and then subscribing to that array using merge.

this.userService.getSelfPurchases().pipe(
  tap(response => this.purchases = response),
  map(purchases => purchases.map((purchase, index) =>
    this.scriptService.getScriptDetails(purchase.script_id).pipe(
      map(responseTwo => ({index, responseTwo}))
    )
  )),
  mergeMap(scriptDetailsCalls => merge(...scriptDetailsCalls)),
).subscribe(({index, responseTwo}) => {
  if (responseTwo[0] && responseTwo[0].sname !== undefined) {
    // append to our original purchases object
    this.purchases[index].sname = responseTwo[0].sname;
  }
});

You can simplify the above code by combining the map and mergeMap into a single mergeMap as shown below:

this.userService.getSelfPurchases().pipe(
  tap(response => this.purchases = response),
  mergeMap(purchases => merge(...
    purchases.map((purchase, index) =>
      this.scriptService.getScriptDetails(purchase.script_id).pipe(
        map(responseTwo => ({index, responseTwo}))
      )
    ))
  )
).subscribe(({index, responseTwo}) => {
  if (responseTwo[0] && responseTwo[0].sname !== undefined) {
    // append to our original purchases object
    this.purchases[index].sname = responseTwo[0].sname;
  }
});

Aside: Avoid global variables

Avoid setting and modifying global variables as it can make testing harder and introduce uncertainties about the state of the variable. Instead, consider a functional approach where variables are scoped appropriately.

this.userService.getSelfPurchases().pipe(
  mergeMap(purchases => forkJoin(
    purchases.map(purchase =>
      this.scriptService.getScriptDetails(purchase.script_id).pipe(
        map(responseTwo => ({...purchase, sname: responseTwo[0].sname}))
      )
    )
  ))
).subscribe(purchasesWName =>
  this.purchases = purchasesWName
);

Answer 2

It is generally advised not to nest subscriptions for the sake of maintainability, extendibility, and readability. Nesting subscriptions can easily lead to callback hell, causing confusion and complexity in the code.

Instead of nesting subscriptions, you can refactor your code by mapping an array of purchases into an array of getScriptDetails calls and then subscribing to that array using merge.

this.userService.getSelfPurchases().pipe(
  tap(response => this.purchases = response),
  map(purchases => purchases.map((purchase, index) =>
    this.scriptService.getScriptDetails(purchase.script_id).pipe(
      map(responseTwo => ({index, responseTwo}))
    )
  )),
  mergeMap(scriptDetailsCalls => merge(...scriptDetailsCalls)),
).subscribe(({index, responseTwo}) => {
  if (responseTwo[0] && responseTwo[0].sname !== undefined) {
    // append to our original purchases object
    this.purchases[index].sname = responseTwo[0].sname;
  }
});

You can simplify the above code by combining the map and mergeMap into a single mergeMap as shown below:

this.userService.getSelfPurchases().pipe(
  tap(response => this.purchases = response),
  mergeMap(purchases => merge(...
    purchases.map((purchase, index) =>
      this.scriptService.getScriptDetails(purchase.script_id).pipe(
        map(responseTwo => ({index, responseTwo}))
      )
    ))
  )
).subscribe(({index, responseTwo}) => {
  if (responseTwo[0] && responseTwo[0].sname !== undefined) {
    // append to our original purchases object
    this.purchases[index].sname = responseTwo[0].sname;
  }
});

Aside: Avoid global variables

Avoid setting and modifying global variables as it can make testing harder and introduce uncertainties about the state of the variable. Instead, consider a functional approach where variables are scoped appropriately.

this.userService.getSelfPurchases().pipe(
  mergeMap(purchases => forkJoin(
    purchases.map(purchase =>
      this.scriptService.getScriptDetails(purchase.script_id).pipe(
        map(responseTwo => ({...purchase, sname: responseTwo[0].sname}))
      )
    )
  ))
).subscribe(purchasesWName =>
  this.purchases = purchasesWName
);

Answer 3

Answer №2

This scenario involves using switchMap, forkJoin, and map functions

Retrieve the initial list of purchases
Generate an array of observables based on the purchases
Leverage forkJoin to combine all observables
Map the original list by adding values from the combined responses

Implementation in code:

this.userService.getSelfPurchases().pipe(
   switchMap(purchases=>{
         // Obtain the list of purchases, for example: [{script_id:2,script_id:4}]
         // Create an array of observables based on the purchases
         const obs=purchases.map(purchase=>this.scriptService.getScriptDetails(purchase.script_id))
        // Use switchmap to return an observable
        return forkJoin(obs).pipe(
            // The data variable contains responses for script_id:2 and script_id4
            // Modify the data format using map function
            map((data:any[])=>{
               // Iterate through purchases to update properties with data
               purchases.forEach((purchase,index)=>{
                  purchase.sname=data[index].sname
                  purchase.author=data[index].author
                  purchase.price=data[index].price
                  purchase.author=data[index].author
               }
               // Return the updated purchases list
               return purchases
            })
        )
   })
)

Answer 4

This scenario involves using switchMap, forkJoin, and map functions

Retrieve the initial list of purchases
Generate an array of observables based on the purchases
Leverage forkJoin to combine all observables
Map the original list by adding values from the combined responses

Implementation in code:

this.userService.getSelfPurchases().pipe(
   switchMap(purchases=>{
         // Obtain the list of purchases, for example: [{script_id:2,script_id:4}]
         // Create an array of observables based on the purchases
         const obs=purchases.map(purchase=>this.scriptService.getScriptDetails(purchase.script_id))
        // Use switchmap to return an observable
        return forkJoin(obs).pipe(
            // The data variable contains responses for script_id:2 and script_id4
            // Modify the data format using map function
            map((data:any[])=>{
               // Iterate through purchases to update properties with data
               purchases.forEach((purchase,index)=>{
                  purchase.sname=data[index].sname
                  purchase.author=data[index].author
                  purchase.price=data[index].price
                  purchase.author=data[index].author
               }
               // Return the updated purchases list
               return purchases
            })
        )
   })
)

Answer 5

Answer №3

Avoid nesting subscriptions within your code.

Consider using techniques such as concat, forkJoin, switchMap, or merge pipes to combine subscriptions effectively.

It is important to note that nesting subscriptions is considered an anti-pattern in coding practices:

Interested in learning more about RxJs observables and nested subscriptions?

Answer 6

Avoid nesting subscriptions within your code.

Consider using techniques such as concat, forkJoin, switchMap, or merge pipes to combine subscriptions effectively.

It is important to note that nesting subscriptions is considered an anti-pattern in coding practices:

Interested in learning more about RxJs observables and nested subscriptions?

Exploring Improved Methods for Implementing Nested Subscriptions in Typescript

Answer №1

Aside: Avoid global variables

Answer №2

Answer №3

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