EF 6 – How to correctly perform parallel queries

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The problem is this:

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.

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

You will need to modify your code to something like this:

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);
}

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