Async Reading Support

[Turnerj]

Look into support for something like Entity Framework's ToListAsync and how hard that might be to implement in the current stack.

[Turnerj]

C# Lang Proposal: https://github.com/dotnet/csharplang/blob/master/proposals/csharp-8.0/async-streams.md
Would add async reading once something like async streams land.

[dongshengfengniaowu]

The default .net core 3.0 Mvc core ,don't support the none async method. When will MongoFramework support the async query ?

[Turnerj]

Not entirely sure what you mean - it doesn't seem that there is an issue using MongoFramework in ASP.NET Core 3 MVC with MongoFramework being sync-only for reads. Controller actions etc still seem to support sync.

Async reads in general for MongoFramework though, I'm really wanting to have the language proposal come through so I can use the IAsyncEnumerator interface and use foreach async internally. The main part is in places like this: https://github.com/TurnerSoftware/MongoFramework/blob/master/src/MongoFramework/Infrastructure/Linq/MongoFrameworkQueryable.cs#L37-L109

If I don't wait for the IAsyncEnumerator etc myself and just implement something that returns Task<IEnumerable<TEntity>>, while it would be an async query to the database, it means all results would be fetched at once rather than one at a time. If you fetch a lot of results, it means a lot of memory being used at once.

If instead the IAsyncEnumerator is used (when it is released, still a language feature that is coming and will only come to .NET Core 3 as far as I know), then you can asynchronously fetch one item at a time.

I made MongoFramework to help me with my own ASP.Net project and I do want async reads, I just don't think the time is right yet till these building blocks (IAsyncEnumerator and foreach async) are available.

[Turnerj]

Here is a good article of the state of affairs: https://stu.dev/iasyncenumerable-introduction/

Other places have implemented their own enumerator or enumerable interfaces etc and while I could, it would be better spending my time implementing the "real" version when it comes in C#8.

[dongshengfengniaowu]

Thank you for your patience !

[Turnerj]

Thinking a little more about this again, if I do attempt to land an async version without IAsyncEnumerator etc, I will need to dig into how the async path for the ExpressionPlanBuilder works. I still can't wrap it in an IEnumerable at any point because I can't await in an enumerator but to MoveNextAsync (from the IAsyncCursor), I would need to unless I only want to support ToArrayAsync() and ToListAsync().

Because of the more complex expression logic due to the changes for indexing/querying, it will be interesting to see how easily I can still do it given the level of reflection. Maybe this might be a catalyst for #87 to come sooner (though that is still a mighty lot of effort to build).

[Turnerj]

This would likely be easier to implement once #112 lands.