The rapid execution of code causing an observable race condition

Question

The rapid execution of code causing an observable race condition

When exporting a CSV file in my code, I encounter a race condition while trying to modify some data before the export. The issue is that the id gets set correctly, but the number only updates after the method is called a second time. I believe the problem lies in the fact that the return statement is being executed before the observable has finished. How can I resolve this issue?

  public exportAsCSV(
    arr: ArrEntity[],
    origin: string,
    id?: string,
  ): Observable<Blob> {
    let headers = new HttpHeaders();

    if (arr && arr.length > 0) {
      headers = headers.append(
        xxx
      );

      if (origin === 'table') {
        this.getValues(3).subscribe(() => {
        for (const a of arr) {
          a.id = id; // works fine

          a.number = this.getNumberById(a.number); // only correct after 2nd call
         }
        });
      }

      return this.http.post(
        url,
        {
          chargeLogEntities: arr,
        },
        {
          headers: headers,
          responseType: 'blob',
        },
      );
    } else {
      return Observable.of();
    }
  }

angular typescript rxjs

Answer 1

Answer №1

To ensure proper execution of your code, it is crucial to avoid mixing synchronous and asynchronous operations. If your logic requires data that is fetched asynchronously, make sure to handle the flow correctly by waiting for the data before proceeding. This can be done through callbacks, Promises with `.then`, or Observables with `.subscribe`.

Another approach is to chain multiple Observables using operators like `flatMap/switchMap/concatMap` to maintain a smooth sequence of operations.

Your revised code snippet may look something like this:

public exportCSV(
    array: Entity[],
    source: string,
    identifier?: string,
  ): Observable<Blob> {
    let headers = new HttpHeaders();

    if (array && array.length > 0) {
      headers = headers.append(
        xxx
      );
      
      let prerequisites$ = of();

      if (source === 'table') {
        prerequisites$ = this.retrieveValues(3).pipe(
           tap(response => {
              for (const item of array) {
                 item.id = id;
                 item.number = this.fetchNumberById(item.number);
                 // Avoid mutating objects/arrays directly, consider returning modified data for further usage
              }
           })
        )
      }

      return prerequisites$.pipe(
         switchMapTo(this.http.post(
           url,
           {
             entities: array,
           },
           {
             headers: headers,
             responseType: 'blob',
           },
         )
      )
    } else {
      return Observable.of();
    }
  }

If you prefer not to mutate the original array, an alternative solution could be implemented as follows:

public exportCSV(
    array: Entity[],
    source: string,
    identifier?: string,
  ): Observable<Blob> {
    let headers = new HttpHeaders();

    if (array && array.length > 0) {
      headers = headers.append(
        xxx
      );

      let updatedArray$ = of(array);

      if (source === 'table') {
        updatedArray$ = this.retrieveValues(3).pipe(
           map(response => {
              return array.map(item => {...item, id: identifier, number: this.fetchNumberById(item.number)}
           })
        )
      }

      return updatedArray$.pipe(
         switchMap(updatedArray => this.http.post(
           url,
           {
             entities: updatedArray,
           },
           {
             headers: headers,
             responseType: 'blob',
           },
         )
      )
    } else {
      return Observable.of();
    }
  }

Utilizing `.pipe(switchMapTo())` or `.pipe(switchMap())` ensures sequential execution of the code.

Answer 2

To ensure proper execution of your code, it is crucial to avoid mixing synchronous and asynchronous operations. If your logic requires data that is fetched asynchronously, make sure to handle the flow correctly by waiting for the data before proceeding. This can be done through callbacks, Promises with `.then`, or Observables with `.subscribe`.

Another approach is to chain multiple Observables using operators like `flatMap/switchMap/concatMap` to maintain a smooth sequence of operations.

Your revised code snippet may look something like this:

public exportCSV(
    array: Entity[],
    source: string,
    identifier?: string,
  ): Observable<Blob> {
    let headers = new HttpHeaders();

    if (array && array.length > 0) {
      headers = headers.append(
        xxx
      );
      
      let prerequisites$ = of();

      if (source === 'table') {
        prerequisites$ = this.retrieveValues(3).pipe(
           tap(response => {
              for (const item of array) {
                 item.id = id;
                 item.number = this.fetchNumberById(item.number);
                 // Avoid mutating objects/arrays directly, consider returning modified data for further usage
              }
           })
        )
      }

      return prerequisites$.pipe(
         switchMapTo(this.http.post(
           url,
           {
             entities: array,
           },
           {
             headers: headers,
             responseType: 'blob',
           },
         )
      )
    } else {
      return Observable.of();
    }
  }

If you prefer not to mutate the original array, an alternative solution could be implemented as follows:

public exportCSV(
    array: Entity[],
    source: string,
    identifier?: string,
  ): Observable<Blob> {
    let headers = new HttpHeaders();

    if (array && array.length > 0) {
      headers = headers.append(
        xxx
      );

      let updatedArray$ = of(array);

      if (source === 'table') {
        updatedArray$ = this.retrieveValues(3).pipe(
           map(response => {
              return array.map(item => {...item, id: identifier, number: this.fetchNumberById(item.number)}
           })
        )
      }

      return updatedArray$.pipe(
         switchMap(updatedArray => this.http.post(
           url,
           {
             entities: updatedArray,
           },
           {
             headers: headers,
             responseType: 'blob',
           },
         )
      )
    } else {
      return Observable.of();
    }
  }

Utilizing `.pipe(switchMapTo())` or `.pipe(switchMap())` ensures sequential execution of the code.

The rapid execution of code causing an observable race condition

Answer №1

Similar questions

Using TypeScript to Return a Derived Class as a Method's Return Type

Incorporating a component specified in a .jsx file into a TypeScript file

Converting a string to Time format using JavaScript

Problem with Angular Slider

Executing a service request in Angular 2 using a versatile function

The type 'Dispatch<SetStateAction<boolean>>' cannot be assigned to type 'boolean'

Step-by-step guide on setting up cosmosDB databases and containers in azure functions with the node sdk

Exploring the zoom functionality and tooltip features of Area Range charts in Highcharts

Having trouble customizing the HTML range input?

The name 'XXX' is nowhere to be found

Stopping HTTP client calls in OnDestroy hook of an Angular Service

The method to create a global generic class in TypeScript

The value of Angular Input remains unchanged within a FormArray

Angular and the feature of contenteditable

Prevent clicking outside the bootstrap modal in Angular 4 from closing the modal

CompositeAPI: Referencing HTML Object Template - Error TS2339 and TS2533 when using .value to access Proxy Object

Tips for personalizing Ion text area in Ionic?

Angular: utilizing two ngFors to target and update specific sections of the DOM

Is there a more effective alternative to using the ternary condition operator for extended periods of time?

Testing the function that relies on a service through a unit test