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refactor: convert offset into a signal model #540

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refactor: convert offset into a signal model #540

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4 changes: 2 additions & 2 deletions projects/ngx-datatable/src/lib/components/datatable.component.html
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Original file line number Diff line number Diff line change
Expand Up @@ -43,7 +43,7 @@
[externalPaging]="externalPaging()"
[rowHeight]="rowHeight()"
[rowCount]="rowCount()"
[offset]="offset"
[offset]="correctedOffset()"
[trackByProp]="trackByProp()"
[columns]="_internalColumns()"
[pageSize]="pageSize()"
Expand Down Expand Up @@ -97,7 +97,7 @@
[rowCount]="_internalGroupedRows() !== undefined ? _internalRows().length : rowCount()"
[groupCount]="_internalGroupedRows() !== undefined ? rowCount() : undefined"
[pageSize]="pageSize()"
[offset]="offset"
[offset]="correctedOffset()"
[footerHeight]="footerHeight()"
[footerTemplate]="_footer()"
[totalMessage]="messages().totalMessage ?? 'total'"
Expand Down
6 changes: 3 additions & 3 deletions projects/ngx-datatable/src/lib/components/datatable.component.spec.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -327,18 +327,18 @@ describe('DatatableComponent', () => {
component.columns = columns;
fixture.detectChanges();

const datatableComponent = fixture.debugElement.query(
const datatableComponent: DatatableComponent = fixture.debugElement.query(
By.directive(DatatableComponent)
).componentInstance;
datatableComponent.offset = 1;
datatableComponent.offset.set(1);

// sort by `id` descending
sortBy({ column: 1 }, fixture);
fixture.detectChanges();
sortBy({ column: 1 }, fixture);
fixture.detectChanges();

expect(datatableComponent.offset).toBe(0);
expect(datatableComponent.offset()).toBe(0);
});

it('should support array data', () => {
Expand Down
39 changes: 22 additions & 17 deletions projects/ngx-datatable/src/lib/components/datatable.component.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -15,7 +15,6 @@ import {
HostListener,
inject,
input,
Input,
IterableDiffer,
IterableDiffers,
linkedSignal,
Expand Down Expand Up @@ -230,12 +229,7 @@ export class DatatableComponent<TRow extends Row = any>
* The current offset ( page - 1 ) shown.
* Default value: `0`
*/
@Input({ transform: numberAttribute }) set offset(val: number) {
this._offset = val;
}
get offset(): number {
return Math.max(Math.min(this._offset, Math.ceil(this.rowCount() / this.pageSize()) - 1), 0);
}
readonly offset = model<number>(0);

/**
* Show the linear loading bar.
Expand Down Expand Up @@ -667,7 +661,6 @@ export class DatatableComponent<TRow extends Row = any>
private readonly _rowDiffCount = signal(0);

_offsetX = 0;
_offset = 0;
readonly _internalRows = computed(() => {
this._rowDiffCount(); // to trigger recalculation when row differ detects a change
let rows = this.rows()?.slice() ?? [];
Expand Down Expand Up @@ -734,6 +727,18 @@ export class DatatableComponent<TRow extends Row = any>
)
)
);

/**
* Computed signal that returns the corrected offset value.
* It ensures the offset is within valid bounds based on rowCount and pageSize.
*/
readonly correctedOffset = computed(() => {
const offset = this.offset();
const rowCount = this.rowCount();
const pageSize = this.pageSize();
return Math.max(Math.min(offset, Math.ceil(rowCount / pageSize) - 1), 0);
});
Comment on lines +735 to +740
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@gemini-code-assist gemini-code-assist bot Nov 25, 2025

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medium

The calculation for correctedOffset can result in NaN if pageSize is 0. This can happen if there are no rows and no limit is set. While this is handled by isNaN checks in other parts of the code, it's more robust to prevent NaN from being generated in the first place. Adding a guard for pageSize === 0 will make the logic clearer and safer.

  readonly correctedOffset = computed(() => {
    const offset = this.offset();
    const rowCount = this.rowCount();
    const pageSize = this.pageSize();
    if (pageSize === 0) {
      return 0;
    }
    return Math.max(Math.min(offset, Math.ceil(rowCount / pageSize) - 1), 0);
  });

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@spike-rabbit spike-rabbit Nov 25, 2025

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@fh1ch this is actually a very valid concern, but I think the proper fix is, to ensure pageSize >= 1 is always true.

I would do this in a follow-up


_subscriptions: Subscription[] = [];
_defaultColumnWidth = this.configuration?.defaultColumnWidth ?? 150;
/**
Expand Down Expand Up @@ -952,14 +957,14 @@ export class DatatableComponent<TRow extends Row = any>
return;
}

this.offset = offset;
this.offset.set(offset);

if (!isNaN(this.offset)) {
if (!isNaN(this.correctedOffset())) {
this.page.emit({
count: this.count(),
pageSize: this.pageSize(),
limit: this.limit(),
offset: this.offset,
offset: this.correctedOffset(),
sorts: this.sorts()
});
}
Expand All @@ -977,14 +982,14 @@ export class DatatableComponent<TRow extends Row = any>
* The footer triggered a page event.
*/
onFooterPage(event: PagerPageEvent) {
this.offset = event.page - 1;
this._bodyComponent().updateOffsetY(this.offset);
this.offset.set(event.page - 1);
this._bodyComponent().updateOffsetY(this.correctedOffset());

this.page.emit({
count: this.count(),
pageSize: this.pageSize(),
limit: this.limit(),
offset: this.offset,
offset: this.correctedOffset(),
sorts: this.sorts()
});

Expand Down Expand Up @@ -1132,14 +1137,14 @@ export class DatatableComponent<TRow extends Row = any>
this.sorts.set(event.sorts);

// Always go to first page when sorting to see the newly sorted data
this.offset = 0;
this._bodyComponent().updateOffsetY(this.offset);
this.offset.set(0);
this._bodyComponent().updateOffsetY(this.correctedOffset());
// Emit the page object with updated offset value
this.page.emit({
count: this.count(),
pageSize: this.pageSize(),
limit: this.limit(),
offset: this.offset,
offset: this.correctedOffset(),
sorts: this.sorts()
});
this.sort.emit(event);
Expand Down
2 changes: 1 addition & 1 deletion src/app/basic/filter.component.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -68,6 +68,6 @@ export class FilterComponent {
return d.name.toLowerCase().includes(val) || !val;
});
// Whenever the filter changes, always go back to the first page
this.table.offset = 0;
this.table.offset.set(0);
}
}
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