c# - EF 6 - 如何正确执行并行查询

Question

创建报告时，我必须执行 3 个涉及相同上下文的不同实体的查询。因为它们很重，所以我决定使用 .ToListAsync(); 让它们并行运行，但令我惊讶的是，我从中得到了一个异常(exception)...

使用 EF 6 并行执行查询的正确方法是什么？我应该手动启动新任务吗？

编辑 1
代码基本上是

using(var MyCtx = new MyCtx())
{
      var r1 = MyCtx.E1.Where(bla bla bla).ToListAsync();
      var r2 = MyCtx.E2.Where(ble ble ble).ToListAsync();
      var r3 = MyCtx.E3.Where(ble ble ble).ToListAsync();
      Task.WhenAll(r1,r2,r3);
      DoSomething(r1.Result, r2.Result, r3.Result);
}

Answer 1

问题是这样的:

EF doesn't support processing multiple requests through the same DbContext object. If your second asynchronous request on the same DbContext instance starts before the first request finishes (and that's the whole point), you'll get an error message that your request is processing against an open DataReader.

来源:https://visualstudiomagazine.com/articles/2014/04/01/async-processing.aspx

您需要将代码修改为如下所示:

async Task<List<E1Entity>> GetE1Data()
{
    using(var MyCtx = new MyCtx())
    {
         return await MyCtx.E1.Where(bla bla bla).ToListAsync();
    }
}

async Task<List<E2Entity>> GetE2Data()
{
    using(var MyCtx = new MyCtx())
    {
         return await MyCtx.E2.Where(bla bla bla).ToListAsync();
    }
}

async Task DoSomething()
{
    var t1 = GetE1Data();
    var t2 = GetE2Data();
    await Task.WhenAll(t1,t2);
    DoSomething(t1.Result, t2.Result);
}