ServerDataSource: Setting filters sends new network request when doEmit=true

[SZOKOZ]

const source = new ServerDataSource(this.http,
      {
        endPoint: `${this.apiUrl}/${uri}`,
        dataKey: '',
        pagerPageKey: 'pageNumber',
        pagerLimitKey: 'pageSize',
        filterFieldKey: 'filterBy#field#',
        sortFieldKey: 'sortBy',
        sortDirKey: 'orderBy',
      });
    source.setFilter([
      {
        field: 'type',
        search: 'engine',
      },
    ]); // Results in a http get request
    source.setPaging(1, 1); // Results in a http get request
    
    // Actual intentional attempt to retrieve data.
    source.getElements().then(response => console.log(response));

Setting the filter calls the parent set filter which emits a filter event calling emitOnChanged leading to a http call with the currently set filter. Setting paging has the same issue.

In the docs the doEmit flag is used to determine whether or not the table is refreshed and theoretically helpful for detecting changes but what it actually does is grossly different.

[uap-universe]

I am not sure if I understand the issue correctly.

Changing the pagination or the filter must result in a http request, because the items of the current page might change.

If the observation is, that an additional http request with the old and outdated filter or pagination is sent, then this is obviously a bug.

Can you please clarify?

[uap-universe]

It looks like the ServerDataSource needs to remember the last query parameters s.t. subsequent calls to

• getAll()
• getElements()
• getFilteredAndSorted()

can return the last result without issuing a new request. On the other hand, there needs to be a way to invalidate this "cache", because otherwise you would not get fresh data from the server.

I would override the refresh() method for this. This way you get new data from the server

• every time the query changes (changing the page or the filter)
• on explicit calls of refresh()

In my opinion the ServerDataSource is a bit broken anyway, because it inherits from LocalDataSource but has completely different semantics. For example I don't know what prepend or empty should mean in the context of a ServerDataSource....

The enhancement is described in ticket #106.

To solve this issue here it only needs a bit more documentation.