How to implement server-side Pagination + server-side Sorting with ngx-datatable

Question

With the Angular component ngx-datatable from Swilane it is possible to use the server-side paging and the server-side sorting.

Both of them are documented, however it is not clear how to combine them and use server side pagination+sorting at the same time.

From the documentation, the pagination automatically calls a callback when the user changes page:

setPage(pageInfo) {
    this.page.pageNumber = pageInfo.offset;
    this.serverResultsService.getResults(this.page).subscribe(pagedData => {
    this.page = pagedData.page;
    this.rows = pagedData.data;
 });

and the same happens with the sorting:

onSort(event) {
    // event was triggered, start sort sequence
    console.log('Sort Event', event);
    this.loading = true;
    // emulate a server request with a timeout
    setTimeout(() => {
      const rows = [...this.rows];
      // this is only for demo purposes, normally
      // your server would return the result for
      // you and you would just set the rows prop
      const sort = event.sorts[0];
      rows.sort((a, b) => {
        return a[sort.prop].localeCompare(b[sort.prop]) * (sort.dir === 'desc' ? -1 : 1);
      });

      this.rows = rows;
      this.loading = false;
    }, 1000);
  }

but how to combine them?

Solution

I figure out that the best way to handle both server-side pagination AND server-side sorting consist of:

• having a page object which holds all the pagination and sorting information (like the order column, order direction, page number, page size, ...) which will be bound to the table

• having a single function reloadTable() which calls the API to get the data using the data stored in the page object as parameters, automaticaly re-rendering the table

• having a pageCallback which only updates the data contained in page relative to the pagination and then calls reloadTable()

• having a sortCallback which only updates the data contained in page relative to the sorting and then calls reloadTable()

example:

import { Component, OnInit } from '@angular/core';
import { HttpClient, HttpParams } from '@angular/common/http';

@Component({
  selector: 'app-my-component',
  template: `
    <ngx-datatable
      class="bootstrap table table-striped"
      [rows]="rows"
      [columns]="columns"
      [columnMode]="'force'"
      [headerHeight]="50"
      [footerHeight]="50"
      [rowHeight]="'auto'"
      [externalPaging]="true"
      [externalSorting]="true"
      [count]="page.count"
      [offset]="page.offset"
      [limit]="page.limit"
      [sortType]="'single'"
      (page)="pageCallback($event)"
      (sort)="sortCallback($event)"
    ></ngx-datatable>
  `
})
export class MyComponent implements OnInit {
  page = {
    limit: 10,
    count: 0,
    offset: 0,
    orderBy: 'myColumn1',
    orderDir: 'desc'
  };

  rows: Object[];

  columns = [
    { name: 'myColumn1' },
    { name: 'myColumn2' },
    { name: 'myColumn3' },
  ];

  constructor(private httpClient: HttpClient) { }

  ngOnInit() {
    this.pageCallback({ offset: 0 });
  }

  /**
   * Called whenever the user changes page
   *
   * check: https://swimlane.gitbooks.io/ngx-datatable/content/api/table/outputs.html
   */
  pageCallback(pageInfo: { count?: number, pageSize?: number, limit?: number, offset?: number }) {
    this.page.offset = pageInfo.offset;
    this.reloadTable();
  }

  /**
   * Called whenever the user changes the sort order
   *
   * check: https://swimlane.gitbooks.io/ngx-datatable/content/api/table/outputs.html
   */
  sortCallback(sortInfo: { sorts: { dir: string, prop: string }[], column: {}, prevValue: string, newValue: string }) {
    // there will always be one "sort" object if "sortType" is set to "single"
    this.page.orderDir = sortInfo.sorts[0].dir;
    this.page.orderBy = sortInfo.sorts[0].prop;
    this.reloadTable();
  }

  /**
   * You will render the table once at the beginning in ngOnInit()
   * and then every time the page OR the sort order are changed
   */
  reloadTable() {

    // NOTE: those params key values depends on your API!
    const params = new HttpParams()
      .set('orderColumn', `${this.page.orderBy}`)
      .set('orderDir', `${this.page.orderDir}`)
      .set('pageNumber', `${this.page.offset}`)
      .set('pageSize', `${this.page.limit}`);

    this.httpClient.get(`http://www.your-api.com/path/resource`, { params })
      .subscribe((data) => {

        // NOTE: the format of the returned data depends on your API!
        this.page.count = data.count;
        this.rows = data.rows;
      });
  }
}