c# - Entity Framework 7(核心): DataReader must be closed exception

Question

我正在使用 EF7(EF 核心)。当我尝试以单一方法更新这样的数据库项目时...

using (var db = new DBContext())
{
    var deadSources =
        await
            db.Source.Where(x => !x.Item.Any())
                .ToListAsync();
    foreach (var srs in deadSources)
    {
        srs.InspectionFailed = true;
        srs.InspectionFailedDescription = "ERROR";
    }
    await db.SaveChangesAsync();
}

using (var db = new DBContext())
{
    var aliveSources =
        await
            db.Source.Where(x => x.Item.Any())
                .ToListAsync();
    foreach (var srs in aliveSources)
    {
        srs.InspectionFailed = false;
        srs.InspectionFailedDescription = string.Empty;
    }
    await db.SaveChangesAsync(); // Exception here
}

...抛出此异常:

There is already an open DataReader associated with this Command which must be closed first.

我怎样才能避免这种情况？每个数据库请求都有两个不同的上下文，所以我不明白为什么会这样。

Answer 1

同一个 DbContext 是否有一个、两个或多个实例并不重要，数据库服务端存在每个连接一个数据读取器的限制，因此您需要在连接字符串中启用 MultipleActiveResultSets 选项:

<add name="XYZ" connectionString="Server=SERVER;Database=DATABASE;
 Trusted_Connection=SSPI;MultipleActiveResultSets=True;"
 providerName="System.Data.SqlClient"/>