Async version of LoadFromQueryable

[tomasherceg]

GridViewDataSet doesn't have the async version of LoadFromQueryable. We should add it.

[exyi]

We can not, IQueryable<T> nor the IQueryProvider does not have any async method - https://docs.microsoft.com/cs-cz/dotnet/api/system.linq.iqueryable-1, https://docs.microsoft.com/cs-cz/dotnet/api/system.linq.iqueryable-1?view=netframework-4.7.2

[quigamdev]

We can create a new package with extensions for EntityFramework. But this method cannot be included in DotVVM Framework package directly. As @exyi mentioned, IQueryable<T> does not provide any async method.

[exyi]

I think that sharing some little snippet that solves the problem would be better than a package as it will let people not using EF change some detail and make it work for them. It may look like this for some hypotetical ORM that needs a IAsyncQueryExecutor

public Task LoadFromQueryable(IQueryable<T> source, IAsyncQueryExecutor e)
{
	source = ApplyFilteringToQueryable(source);
	var itemsTask = e.GetListAsync(ApplyOptionsToQueryable(source));
	var totalItemsTask = e.GetCountAsync(source);

	await Task.WhenAll(itemsTask, totalItemsTask);
	Items = itemsTask.Result;
	PagingOptions.TotalItemsCount = totalItemsTask.Result;
	IsRefreshRequired = false;
}

[tomasherceg]

I have found the System.Linq.Async package that should add ToListAsync - it's prerelease and unlisted now, but it's there. We should explore whether this can help us.

[exyi]

In EF Core, the IQueryable implements IAsyncEnumerable which is in the standard. This means that we can actually implement this method (at least for netstandard2.1 version)

[exyi]

Ok, it's not that easy since we also need to call the .Count() method, which does not have an async variant in netstandard2.1 :|