为什么 Entity Framework 忽略 TransactionScope（不添加 NOLOCK）？

Question

我错过了什么？

我正在尝试使用这样的 TransactionScope 使用 NOLOCK 进行读取：

var scopeOptions = new TransactionOptions { IsolationLevel = IsolationLevel.ReadUncommitted };
using (var scope = new TransactionScope(TransactionScopeOption.Required, scopeOptions))
{
   using (var db = new MyDbContext(ConnectionStringEntities))
   {
      // Simple read with a try catch block...
   }
   scope.Complete();
}

我希望看到将 NOLOCK 添加到 SQL 查询中（查看 SQL Profiler 以及自定义 DbCommandInterceptor - 但它不存在...

更新： 经过更多研究，我想知道是否最终使用了选定的游标，只是没有 NOLOCK "hint" (SQL 服务器特定的 - 也特定于一个 table)，我发现了一些获取当前事务的代码，它似乎显示了正确选择的事务隔离（ReadUncommitted / Serializable 等）我仍然想测试它但让我知道你有什么想法

Get current .net TransactionScope IsolationLevel

Transaction trans = Transaction.Current;
System.Transactions.IsolationLevel level = trans.IsolationLevel;
LogService.Instance.Debug($"Transaction IsolationLevel = {level.ToString()}");

Answer 1

您无法 Entity Framework 呈现 NOLOCK 提示。如果你想读取未提交的数据，你必须做一些不同的事情，就像你通过将带有 IsolationLevel.ReadUncommited 的 TransactionScope 添加到 TransactionOptions 所做的那样。

编写您自己的命令拦截器或您自己的 EF 提供程序也可以。

https://msdn.microsoft.com/en-us/data/dn469464.aspx

Answer 2

所以看起来 Entity Framework 确实尊重 IsolationLevel，只是它不使用 NOLOCK 提示（可能是因为它过于特定于数据库），顺便说一下，我对 EF 的主要抱怨是对于不同的数据库类型不是很优化，另一个例子是新身份将 AspNetUsers 的 GUID 主键保存为字符串（同样是因为缺乏优化）除此之外（和其他一些东西）EF 很棒！

我在任何地方都找不到解决我的问题的方法，我绝对不想让我的所有查询都使用 NOLOCK - 只是未提交的查询，所以我最终结合了两个解决方案（有一些变化）：

NoLockInterceptor - 用于动态添加 NOLOCK (Entity Framework with NOLOCK):

/// <summary>
/// Add "WITH (NOLOCK)" hint to SQL queries, SQL Server specifc - may break queries on different databases.
/// (conditionally turn off with NoLockInterceptor.AddNoLockHintToSqlQueries = false to change on runtime)
/// <para>
/// 
/// </para>
/// </summary>
public class NoLockInterceptor : DbCommandInterceptor
{
    private static readonly Regex TableAliasRegex = new Regex(
        @"(?<tableAlias>AS \[Extent\d+\](?! WITH \(NOLOCK\)))",
        RegexOptions.Multiline | RegexOptions.IgnoreCase);

    /// <summary>
    /// Add "WITH (NOLOCK)" hint to SQL queries - unique to each thread 
    /// (set to true only when needed and then back to false)
    /// </summary>
    [ThreadStatic]
    public static bool AddNoLockHintToSqlQueries;

    public NoLockInterceptor()
    {
        // Do not use by default for all queries
        AddNoLockHintToSqlQueries = false;
    }

    public override void ScalarExecuting(DbCommand command, DbCommandInterceptionContext<object> interceptionContext)
    {
        if (AddNoLockHintToSqlQueries)
        {
            command.CommandText = TableAliasRegex.Replace(command.CommandText, "${tableAlias} WITH (NOLOCK)");
        }
    }

    public override void ReaderExecuting(DbCommand command, DbCommandInterceptionContext<DbDataReader> interceptionContext)
    {
        if (AddNoLockHintToSqlQueries)
        {
            command.CommandText = TableAliasRegex.Replace(command.CommandText, "${tableAlias} WITH (NOLOCK)");
        }
    }
}

TransactionWrapper - 调用 NoLockInterceptor 行为并且对于重复使用事务也很有用 (http://haacked.com/archive/2009/08/18/simpler-transactions.aspx/):

/// <summary>
/// Transaction wrapper for setting pre-defined transaction scopes
/// <para>
/// http://haacked.com/archive/2009/08/18/simpler-transactions.aspx/
/// </para>
/// </summary>
public static class TransactionWrapper
{
    /// <summary>
    /// Set transaction scope and using NoLockInterceptor for adding SQL Server specific "WITH (NOLOCK)" 
    /// to ReadUncommitted isolation level transactions (not supported by Entity Framework)
    /// </summary>
    /// <param name="isolationLevel"></param>
    /// <param name="transactionScopeOption"></param>
    /// <param name="timeout"></param>
    /// <param name="action"></param>
    public static void SetScope(IsolationLevel isolationLevel, TransactionScopeOption transactionScopeOption,
        TimeSpan timeout, Action action)
    {
        var transactionOptions = new TransactionOptions { IsolationLevel = isolationLevel, Timeout = timeout };
        using (var transactionScope = new TransactionScope(transactionScopeOption, transactionOptions))
        {
            if (isolationLevel == IsolationLevel.ReadUncommitted)
                NoLockInterceptor.AddNoLockHintToSqlQueries = true;

            action();
            transactionScope.Complete();

            if (isolationLevel == IsolationLevel.ReadUncommitted)
                NoLockInterceptor.AddNoLockHintToSqlQueries = false;
        }
    }
}

这样使用：

var timeout = TimeSpan.FromSeconds(ConfigVariables.Instance.Timeout_Transaction_Default_In_Seconds);
TransactionWrapper.SetScope(IsolationLevel.ReadUncommitted, TransactionScopeOption.Required, timeout, () =>
{
    using (var db = new MyDbContext(MyDbContextConnectionStringEntities))
    {
       // Do stuff...
    }
});

NOLOCK 现在仅添加到具有 ReadUncommitted 事务隔离级别范围的查询。

Answer 3

我试过事务作用域，然后它分析了对数据库的调用。 EF 开始和结束事务，但从不更改 Read Committed 的隔离级别。

            using (var scope = new TransactionScope(
            TransactionScopeOption.Required,
            new TransactionOptions()
            {
                IsolationLevel = System.Transactions.IsolationLevel.ReadUncommitted
            }))
        {
            List<T> toReturn = query.ToList();
            scope.Complete();
            return toReturn;
        }

为什么 Entity Framework 忽略 TransactionScope（不添加 NOLOCK）？

Why does Entity Framework ignore TransactionScope (not adding with NOLOCK)?

entity-framework

nolock

transactionscope

entity-framework-6