我错过了什么?

我正在尝试使用这样的 TransactionScope 使用 NOLOCK 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 和自定义 DbCommandInterceptor - 但它不存在......

更新: 经过更多研究后,我想知道是否正在使用选定的游标,只是没有 NOLOCK“提示”(SQL Server 特定 - 也特定于一个表),我发现了一些获取当前信息的代码事务,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,但如果您有任何想法,请告诉我

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

最佳答案

所以看起来 Entity Framework 确实尊重 IsolationLevel,只是它不使用 NOLOCK 提示(可能是因为它太特定于数据库),顺便说一句,我对 EF 的主要提示 - 它没有针对不同的数据库类型进行非常优化,另一个例子是新身份将 AspNetUsers 的 GUID 主键保存为字符串(再次因为缺乏优化),除此之外(以及其他一些事情)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>
    /// https://stackoverflow.com/questions/926656/entity-framework-with-nolock
    /// </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,也可用于重复使用事务 (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;
            }
        }
    }
    

  • 像这样使用它:
    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中。

    关于entity-framework - 为什么 Entity Framework 会忽略 TransactionScope(不添加 NOLOCK)?,我们在Stack Overflow上找到一个类似的问题:https://stackoverflow.com/questions/36386801/

    10-13 02:07