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):
/// <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)");
}
}
}
/// <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/