feat(MatSort): Enable multi-sorting capability on current Interface

[imerljak]

Feature Description

Currently MatSort has a simplistic design that enables sorting only on one column at a time.

Most of enterprise level applications should need multi-sorting capabilities on its datasets. And having it included would be really nice.

In simple terms, my proposal would be to expose a boolean input matMultiSort flag and refactor MatSort and MatSortHeader so that MatSort will hold the MatSortable's state, and expose isActive(id: string) => boolean and getNextDirection(id: string) => SortDirection that will be used instead of directly accessing active and direction.

MatSort will hold a sortState: Map<string, Sort> that can be used to query its state whenever a sort event occurs.

This change should avoid most (if not all) compatibility issues. But it would be best if we can deprecate the current sortChanged: EventEmitter<Sort> for one that emits Sort[] instead, this way we wont need to expose sortState (although most of the usage examples for this API expect one to access its internal state anyway).

Known issues

This change of sorting behavior will require a review of the included sorting method for MatTableDataSource, that was designed around a single column sort. Having multiple possible sortable columns will require a better strategy on sorting (weighting by index position?). Or, whenever the MatTableDataSource default implementation is used, multi-sorting could be disabled?

Use Case

We want to be able to enable sorting based on multiple columns at a time.

This should be done with minimal changes.

Proposed usage:

<!-- Adding matSortMultiple will enable multi-sorting -->
<table mat-table matSort matSortMultiple matSortActive="position" matSortDirection="asc" [dataSource]="dataSource">
    <ng-container matColumnDef="name">
    <th mat-header-cell *matHeaderCellDef mat-sort-header sortActionDescription="Sort by name">
      Name
    </th>
    <td mat-cell *matCellDef="let element"> {{element.name}} </td>
  </ng-container>

<ng-container matColumnDef="symbol">
    <th mat-header-cell *matHeaderCellDef mat-sort-header sortActionDescription="Sort by symbol">
      Symbol
    </th>
    <td mat-cell *matCellDef="let element"> {{element.symbol}} </td>
  </ng-container>
</table>

@ViewChild(MatSort) matSort: MatSort;

ngAfterViewInit() {
    matSort.sortChanged.pipe(map(() => Array.from(matSort.sortstate.values()))
    .subscribe((sorts: Sort[])=> {
        // do something with the Sort[] 
    });
}

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[dzaunerOci]

Is it possible to start the voting process again, this feature would be very helpful.

[zarend]

Hello @imerljak,

Would you like to send us a PR for this? This feature request is open source, and anyone is welcome to work on it.

We have a requirement to be backwards compatible, so any PR would need to add multi-sorting without breaking the existing "single-sorting". If the PR changes the sort behavior when not multi-sorting, then we might need an opt-out or opt-in.

Best Regards,

Zach

[imerljak]

Hello @imerljak,

Would you like to send us a PR for this? This feature request is open source, and anyone is welcome to work on it.

We have a requirement to be backwards compatible, so any PR would need to add multi-sorting without breaking the existing "single-sorting". If the PR changes the sort behavior when not multi-sorting, then we might need an opt-out or opt-in.

Best Regards,

Zach

I have the required changes at my cloned repo. But will need to checkout if it is still working as expected since it has been some time already.

Will find some time to rebase it and run the tests again to see if it still works and open a PR.

If I recall correctly it is indeed backwards compatible. Or very close to.

Can't commit to a date though but will try to look into it as soon as possible.

[zarend]

No problem, let us know if you have questions.

[imerljak]

@zarend Opened the MR with the changes for adding multi-sort.

Reviewed my previous implementation in order to avoid any kind of conflicts with current sorting behaviour. So, unless we want to keep track of the current internal sorting state, just toggling the multi-sort flag is enough to make it work.

From what I was able to test on the sorting algorithm it is working as expected, and the behaviour is exactly the same as we have in this other lib which I used as a comparison. For both sorting on multiple columns, as with the order in which we toggle the sorting and cycle through it.

No fancy shift metakey though.. didn't think it was needed atm.

Waiting for feedback over there.. https://github.com/angular/components/pull/28458