Issue #1239 resolution - QueryAsync missing buffered parameter

[SoftStoneDevelop]

This change resolves #1239.

I had to switch to net48;netstandard2.1 because of the Microsoft.Bcl.AsyncInterfaces and System.Linq.Async packages, but I think it's worth it.

[SoftStoneDevelop]

It would be nice to add an asynchronous connection close to the method:

private static async IAsyncEnumerable<T> QueryAsync<T>(this IDbConnection cnn, Type effectiveType, CommandDefinition command)

But I didn’t want to do something like TryOpenAsync, so I made a proposal in .NET to create an IAsyncDbConnection interface:
dotnet/runtime#81723

[mgravell]

Right; so: I don't think we can take this as-is; there's way too much API breakage here, and honestly, taking buffered as a parameter here is just a bad choice, as buffered and unbuffered are fundamentally incompatible shapes

IMO the correct change here is just the addition of a single API:

public static IAsyncEnumerable<T> QueryUnbufferedAsync<T>(this DbConnection cnn, string sql, object param = null,
    DbTransaction transaction = null, int? commandTimeout = null, CommandType? commandType = null)

key points here:

• there's no point pretending IDbConnection will work; it won't; that was a bad API choice in the past
• no buffered parameter

if you care to refactor to just the above, we should be able to take that, but I suspect it may be easier to start from a clean slate and just re-apply the interesting bits; alternatively I'm happy to take this and re-do from scratch

[mgravell]

on the TFM change: I don't see why we need System.Linq.Async - if we just use Microsoft.Bcl.AsyncInterfaces, we get to keep all the TFMs IIRC

[mgravell]

this feature now essentially provided via #1912; I propose we close this and re-evaluate any missing requirements when that is merged