为什么内部 TransactionScope 的 IsolationLevel 不能不同，而 SQL 事务可以不同？

Question

在数据库事务中更改隔离级别是可以的，包括将一个事务加入已经运行的情况。从现在开始，您只需更改处理锁的方式即可。使用 Sql 服务器，运行没有问题：

begin transaction 
set transaction isolation level serializable;
select * from FooTable;

set transaction isolation level read committed;
select * from FooTable;

begin transaction
set transaction isolation level serializable;
select * from FooTable;
--transaction_isolation_level can be observed as 4 (serializable)

但是，当使用 .NET TransactionScope 在上述 Sql 服务器中创建交易时，像这样（C#、xUnit）：

[Theory]
[AutoFixtureMagicToGetParameterInstances]
void ZmenaIzolacniUrovneVedeKVyjimce(IFooDao sut, Foo foo)
{
    var tranOpts = new TransactionOptions()
    {
        IsolationLevel = IsolationLevel.Serializable,
        Timeout = TimeSpan.FromSeconds(60)
    };
    var tranOpts2 = new TransactionOptions()
    {
        IsolationLevel = IsolationLevel.ReadCommitted,
        Timeout = TimeSpan.FromSeconds(60)
    };
    using (var transactionScope = new TransactionScope(TransactionScopeOption.Required, tranOpts))
    {
        sut.SelectFoos();
        using (var transactionScope2 = new TransactionScope(TransactionScopeOption.Required, tranOpts2))
        {
            sut.SelectFoos();
        }
    }
}

导致异常：

System.ArgumentException : The transaction specified for TransactionScope has a different IsolationLevel than the value requested for the scope.
 Parameter name: transactionOptions.IsolationLevel

为什么 TransactionScope 的设计者认为有必要立即抛出异常？

我希望至少只要只涉及数据库资源，行为就会相同。是否有关于 TransactionScope 的内容我遗漏了，或者仅仅是因为无法保证所有可能的征用资源的合理行为？

Answer 1

如此处评论所述Inner TransactionScope with different IsolationLevel, how can it be achieved?

TransactionScope is not limited to use with SQL Server, it can allow distributed transactions across processes/systems. So it is stricter than what SQL Server allows, likely to simplify the complexity of ensuring consistency across the systems than support distributed transactions. – AaronLS

所以答案基本上似乎可以归结为 "TransactionScope may have way more on it's plate than just database transaction and so it forbids complexities like changing isolation levels"。

为什么内部 TransactionScope 的 IsolationLevel 不能不同，而 SQL 事务可以不同？

Why inner TransactionScope's IsolationLevel cannot be different, while SQL transactions can be?

c#

transactions

transactionscope