13 ByStepQuery

In the previous workshop you saw how to use PaginatedQuery.

There is another strategy that can be used for long list that is often used with search: the loading by step.
So, in order to avoid to wait a long time when you are loading a list that might contain thousands elements, you can load them 100 by 100 with a stop button and when you type a new character on your search, you stop the previous query and start a new one.

So in this workshop you will modify the previous popup to use this new one:

WAQS provides a mechanism similar to the PaginatedQuery for thos scenario.

Indeed, you can call the method ToByStepQuery on WAQS LINQ queries.

So in the workshop, you search products that contains a text set in a specific TextBox.

First, update the ProductsWindow.xaml with this xaml.

Then replace the ProductsPaginatedQuery by this:

private ByStepQuery<Product> _productsByStepQuery;
public ByStepQuery<Product> ProductsByStepQuery
{
    get { return _productsByStepQuery; }
    private set
    {
        _productsByStepQuery = value;
        NotifyPropertyChanged.RaisePropertyChanged(nameof(ProductsByStepQuery));
    }
}

Then define the FullNextSearch property.

private string _fullNameSearch;
public string FullNameSearch
{
    get { return _fullNameSearch; }
    set
    {
        _fullNameSearch = value;
        NotifyPropertyChanged.RaisePropertyChanged(nameof(FullNameSearch));
        if (ProductsByStepQuery != null)
        {
            ProductsByStepQuery.Completed -= ProductsByStepQueryCompleted;
            ProductsByStepQuery.Cancel();
        }
        if (string.IsNullOrEmpty(value))
        {
            ProductsByStepQuery = null;
        }
        else
        {
            ProductsByStepQuery =
                (from p in _context.Products.AsAsyncQueryable()
                    let fullName = p.FullName
                    where fullName.Contains(value)
                    orderby fullName, p.Id
                    select new Product { Id = p.Id, FullName = fullName }).ToByStepQuery(10);
            ProductsByStepQuery.Completed += ProductsByStepQueryCompleted;
            ProductsByStepQuery.Load();
            RefreshStopSearchCommandCanExecute();
        }
    }
}

private void ProductsByStepQueryCompleted()
{
    ProductsByStepQuery.Completed -= ProductsByStepQueryCompleted;
    RefreshStopSearchCommandCanExecute();
}

And the StopSearchCommand.

private RelayCommand _stopSearchCommand;
public ICommand StopSearchCommand
{
    get
    {
        return _stopSearchCommand ??
            (_stopSearchCommand = new RelayCommand(
                () => ProductsByStepQuery.Cancel(),
                () => ProductsByStepQuery != null && !ProductsByStepQuery.IsCompleted));
    }
}

private void RefreshStopSearchCommandCanExecute()
{
    if (_stopSearchCommand != null)
    {
        _stopSearchCommand.RaiseCanExecuteChanged();
    }
}

And here you are.

You can find the solution here.