Angular Material table sorting issue: TypeError when initializing

Courses
1

I’m facing an issue with my Angular Material table setup. I initialize an observable in ngOnInit and attach sorting and pagination to my datasource. Everything seems correct, yet I encounter a TypeError.

Here is a revised version of my code:

customDataSource = new CustomTable(this.records);

@ViewChild(CustomPaginator) customPaginator: any = CustomPaginator;
@ViewChild(CustomSort) customSort: any = CustomSort;

initializeView() {
  this.customDataSource.customPaginator = this.customPaginator;
  this.customDataSource.customSort = this.customSort;
}

initializeData(): void {
  this.dataProvider.getData().subscribe((response: any) => {
    this.records = response.records;
    this.customDataSource = new CustomTable(this.records);
    this.customDataSource.customSort = this.customSort;
    this.customDataSource.customPaginator = this.customPaginator;
  })
}

However, I keep seeing this error message:

TypeError: Expected a stream, got 'undefined'. You can use Observable, Promise, ReadableStream, Array, AsyncIterable, or Iterable.

Can anyone point out what might be causing this problem and how to resolve it?

2

Hey Mia_79Dance! :wave:

Hmm, that TypeError is a tricky one. Have you double-checked that your dataProvider.getData() method is actually returning an Observable? Sometimes these stream-related errors pop up when we’re not handling async data quite right.

Also, I’m curious about your CustomTable class. Is it extending MatTableDataSource? If not, that could be part of the issue.

One thing you might try is to defer the datasource initialization until after the data arrives:

initializeData(): void {
  this.dataProvider.getData().pipe(
    tap((response: any) => {
      this.records = response.records;
      this.customDataSource = new CustomTable(this.records);
    }),
    delay(0)  // This ensures ViewChild references are available
  ).subscribe(() => {
    this.customDataSource.customSort = this.customSort;
    this.customDataSource.customPaginator = this.customPaginator;
  });
}

This approach might help avoid timing issues with ViewChild references. Let me know if that helps or if you need to dig deeper!

3

From my experience, this error often occurs when there’s a mismatch between the expected and actual data types. Have you verified that the ‘records’ property in your response is indeed an array? Sometimes backend changes can lead to unexpected data structures.

Another potential issue could be in your CustomTable class implementation. Make sure it correctly handles the input data and implements the necessary methods for sorting and pagination.

You might also want to try moving the datasource initialization to ngAfterViewInit() instead of ngOnInit(). This ensures that the ViewChild decorators have been resolved before you attempt to use them.

Lastly, consider adding some error handling to your observable subscription. This can help pinpoint where exactly the error is occurring in your data flow.

If these suggestions don’t resolve the issue, you may need to share more details about your CustomTable class and the structure of your API response for further debugging.