具有多个上下文的异步调用

Question

所以我的代码伪类似于（依赖注入）：

public DbContextA DBA { get; set; } // SQL Server 1
public DbContextB DBB { get; set; } // SQL Server 2

我现在确定如何最有效地执行以下操作？

public Task<ActionResult> MyAction()
{
  var trucks = await DBA.GetTrucksAsync();
  var cars = DBA.GetCarsAsync();

  var cats = await DBB.GetCatsAsync();
  var dogs = DBB.GetDogsAsync();

  await TaskEx.WhenAll(cars, dogs);
}

除非我记错了，否则这不是最佳选择。我认为能够做到这一点会很棒：

public Task<ActionResult> MyAction()
{
  IEnumerable<Truck> trucks;
  IEnumerable<Car> cars;
  IEnumerable<Cat> cats;
  IEnumerable<Dog> dogs

  var dba = Task.Run(async () => { trucks = await DBA.GetTrucksAsync(); } )
    .ContinueWith(async () => { cars = await DBA.GetCarsAsync(); } );

  var dbb = Task.Run(async () => { cats = await DBB.GetCatsAsync(); })
    .ContinueWith(async () => { dogs = await DBB.GetDogsAsync(); });

  await Task.WhenAll(dba, dbb);
}

但我目前无法对此进行测试（而且我很确定这是错误的）。

Answer 1

只需添加几个方法来表示依赖关系：

private async Task<Tuple<IEnumerable<Truck>, IEnumerable<Car>>> GetVehiclesAsync()
{
  var trucks = await DBA.GetTrucksAsync();
  var cars = await DBA.GetCarsAsync();
  return Tuple.Create(trucks, cars);
}

private async Task<Tuple<IEnumerable<Cat>, IEnumerable<Dog>>> GetAnimalsAsync()
{
  var cats = await DBB.GetCatsAsync();
  var dogs = await DBB.GetDogsAsync();
  return Tuple.Create(cats, dogs);
}

public Task<ActionResult> MyAction()
{
  var vehiclesTask = GetVehiclesAsync();
  var animalsTask = GetAnimalsAsync();
  await Task.WhenAll(vehiclesTask, animalsTask);
}

具有多个上下文的异步调用

Async calling with multiple contexts

asp.net-mvc

async-await

dbcontext

entity-framework-6