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 NOLOCK 添加到 SQL 查询(查看 SQL Profiler 和自定义 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“提示”(特定于 SQL Server - 也特定于一个表),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),顺便说一下,我主要提示 EF - 它没有针对不同的数据库类型,另一个例子是新身份将 AspNetUsers 的 GUID 主键保存为字符串(同样因为缺乏优化),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(有一些更改):
NoLockInterceptor - 用于即时添加 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。
关于entity-framework - 为什么 Entity Framework 会忽略 TransactionScope(不使用 NOLOCK 添加)?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/36386801/