Waiting for a function to complete its processing loop in Angular 7

Question

Waiting for a function to complete its processing loop in Angular 7

In my code, I'm dealing with an angular entity called Z which has a property that is a list of another entity named Y. My goal is to delete the entity Z, but before doing so, I need to also delete all the Y entities within it. The challenge arises from foreign key constraints in the database, which require me to delete all instances of Y before deleting Z.

onDelete(id: number, name: string, Y: Y[]) {
    this.deleteYInZ(Y);
    this.ZService.deleteZ(this.selectedSecuritySubject.value, id).subscribe(() => {
      this.getAllZ();
      }
  }

The method deleteYInZ looks like this:

 deleteYInZ(Y: Y[]) {
    for (const Yentity of Y) {
      this.targetService.deleteTarget(this.selectedSecuritySubject.value, Yentity .ID).subscribe(() => {
      });
    }
  }

I'm facing an asynchronous issue here as I tried to make the deleteYInZ async and then used an await in the onDelete method, but it's not functioning correctly.

Can someone guide me on how I can properly handle the deletion process by first removing all Y entities before proceeding to remove all Z entities?

angular typescript asynchronous subscribe

Answer 1

Answer №1

To accomplish this task, you have the option of utilizing an external async/await function or taking advantage of the new for...of iteration method (which is currently being used).

for (const theY of Y) {
  await yourDeleteFunction(theY);
}

However, if possible, I recommend adjusting your approach if you have access to the backend. Instead of employing forEach, for...of, or any other form of iteration, consider implementing a bulk delete operation. This way, you can reduce the number of requests sent to the backend and also minimize database executions. Here's an example:

deleteZInz(id: number, name: string, items: Y[]) {
  this.deleteYInz(items)
    .subscribe(result => {
      this.ZService.deleteZ(...etc);
    });
}

deleteYInz(items: Y[]): Observable<yourReturnType> {
  return this.targetService.deleteBulk(
    this.selectedSecuritySubject.value,
    items.map(item => item.id),
  );
}

By following this approach, let's say you are working with a MySQL database, you will only be performing one delete operation by using a where in (1, 2, 3, 4, n) clause instead of making separate requests for each of your Y items.

Answer 2

To accomplish this task, you have the option of utilizing an external async/await function or taking advantage of the new for...of iteration method (which is currently being used).

for (const theY of Y) {
  await yourDeleteFunction(theY);
}

However, if possible, I recommend adjusting your approach if you have access to the backend. Instead of employing forEach, for...of, or any other form of iteration, consider implementing a bulk delete operation. This way, you can reduce the number of requests sent to the backend and also minimize database executions. Here's an example:

deleteZInz(id: number, name: string, items: Y[]) {
  this.deleteYInz(items)
    .subscribe(result => {
      this.ZService.deleteZ(...etc);
    });
}

deleteYInz(items: Y[]): Observable<yourReturnType> {
  return this.targetService.deleteBulk(
    this.selectedSecuritySubject.value,
    items.map(item => item.id),
  );
}

By following this approach, let's say you are working with a MySQL database, you will only be performing one delete operation by using a where in (1, 2, 3, 4, n) clause instead of making separate requests for each of your Y items.

Answer 3

Answer №2

Consider implementing a promise in this workflow by utilizing the then operator within the delete function. This way, the return will only occur after the completion of the 'for' loop.

onDelete(id: number, name: string, Y: Y[]) {
this.deleteYInZ(Y).then(_ => {
    this.ZService.deleteZ(this.selectedSecuritySubject.value, id).subscribe(() => {
    this.getAllZ();
  });

}

deleteYInZ(Y: Y[]) {
  return Promise.resolve().then(function () {
    for (const Yentity of Y) {
      this.targetService.deleteTarget(this.selectedSecuritySubject.value,Yentity.ID).subscribe(() => {
      });
    }
  })

}

Answer 4

Consider implementing a promise in this workflow by utilizing the then operator within the delete function. This way, the return will only occur after the completion of the 'for' loop.

onDelete(id: number, name: string, Y: Y[]) {
this.deleteYInZ(Y).then(_ => {
    this.ZService.deleteZ(this.selectedSecuritySubject.value, id).subscribe(() => {
    this.getAllZ();
  });

}

deleteYInZ(Y: Y[]) {
  return Promise.resolve().then(function () {
    for (const Yentity of Y) {
      this.targetService.deleteTarget(this.selectedSecuritySubject.value,Yentity.ID).subscribe(() => {
      });
    }
  })

}

Answer 5

Answer №3

When using for loops or for each loops in Javascript that involve asynchronous actions, they can present unexpected challenges due to their behavior. In most cases, the for loop will complete before the asynchronous actions, leading to confusion. Here is a suggestion to help navigate this issue:

async onDelete(id: number, name: string, Y: Y[]) {
    await this.deleteYInZ(Y);
    ...
}

async deleteYInZ(Y: Y[]) {
    await this.asyncForEach(Y, async (Yentity) => {
        await this.targetService.deleteTarget(this.selectedSecuritySubject.value, Yentity.ID);
    });
}

async asyncForEach(array, callback) {
    for (let index = 0; index < array.length; index++) {
        await callback(array[index], index, array);
    }
}

Additionally, it's important to avoid subscribing to everything when dealing with inner observable loops. Instead, consider piping and returning observables using tools like mergeMap. This helps prevent issues like strange behavior and memory leaks. While this topic extends beyond the current question, I recommend exploring rxjs and adopting a more reactive approach.

Answer 6

When using for loops or for each loops in Javascript that involve asynchronous actions, they can present unexpected challenges due to their behavior. In most cases, the for loop will complete before the asynchronous actions, leading to confusion. Here is a suggestion to help navigate this issue:

async onDelete(id: number, name: string, Y: Y[]) {
    await this.deleteYInZ(Y);
    ...
}

async deleteYInZ(Y: Y[]) {
    await this.asyncForEach(Y, async (Yentity) => {
        await this.targetService.deleteTarget(this.selectedSecuritySubject.value, Yentity.ID);
    });
}

async asyncForEach(array, callback) {
    for (let index = 0; index < array.length; index++) {
        await callback(array[index], index, array);
    }
}

Additionally, it's important to avoid subscribing to everything when dealing with inner observable loops. Instead, consider piping and returning observables using tools like mergeMap. This helps prevent issues like strange behavior and memory leaks. While this topic extends beyond the current question, I recommend exploring rxjs and adopting a more reactive approach.

Waiting for a function to complete its processing loop in Angular 7

Answer №1

Answer №2

Answer №3

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