使用NOLOCK的实体框架

Question

如何NOLOCK在Entity Framework上使用该功能？XML是唯一的方法吗？

Answer 1

不,但您可以启动事务并将隔离级别设置为uncommited.这基本上与NOLOCK相同,但它不是基于每个表执行,而是针对事务范围内的所有内容执行此操作.

如果这听起来像你想要的那样,这就是你如何去做...

//declare the transaction options
var transactionOptions = new System.Transactions.TransactionOptions();
//set it to read uncommited
transactionOptions.IsolationLevel = System.Transactions.IsolationLevel.ReadUncommitted;
//create the transaction scope, passing our options in
using (var transactionScope = new System.Transactions.TransactionScope(
    System.Transactions.TransactionScopeOption.Required, 
    transactionOptions)
)

//declare our context
using (var context = new MyEntityConnection())
{
    //any reads we do here will also read uncomitted data
    //...
    //...
    //don't forget to complete the transaction scope
    transactionScope.Complete();
}

Answer 2

扩展方法可以使这更容易

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

public static int CountReadUncommitted<T>(this IQueryable<T> query)
{
    using (var scope = new TransactionScope(
        TransactionScopeOption.Required, 
        new TransactionOptions() { 
            IsolationLevel = System.Transactions.IsolationLevel.ReadUncommitted }))
    {
        int toReturn = query.Count();
        scope.Complete();
        return toReturn;
    }
}

Answer 3

如果你需要大量的东西,我们找到的最好的方法是每次实际启动一个事务管理器,那么在你通过运行这个简单的命令创建对象上下文之后,只需设置连接上的默认事务隔离级别:

this.context.ExecuteStoreCommand("SET TRANSACTION ISOLATION LEVEL READ UNCOMMITTED;");

http://msdn.microsoft.com/en-us/library/aa259216(v=sql.80).aspx

通过这种技术,我们能够创建一个简单的EF提供程序,为我们创建上下文,并且每次为我们的所有上下文实际运行此命令,以便我们始终处于"未提交读取"状态.

Answer 4

虽然我绝对同意使用Read Uncommitted事务隔离级别是最好的选择,但有些时候你被迫通过经理或客户端的请求使用NOLOCK提示并且没有理由反对这种接受.

使用Entity Framework 6,您可以像这样实现自己的DbCommandInterceptor:

public class NoLockInterceptor : DbCommandInterceptor
{
    private static readonly Regex _tableAliasRegex = 
        new Regex(@"(?<tableAlias>AS \[Extent\d+\](?! WITH \(NOLOCK\)))", 
            RegexOptions.Multiline | RegexOptions.IgnoreCase);

    [ThreadStatic]
    public static bool SuppressNoLock;

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

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

有了这个类,您可以在应用程序启动时应用它:

DbInterception.Add(new NoLockInterceptor());

并有条件地关闭添加NOLOCK提示到当前线程的查询:

NoLockInterceptor.SuppressNoLock = true;

Answer 5

加强琼斯博士接受的答案并使用PostSharp ;

第一个" ReadUncommitedTransactionScopeAttribute "

[Serializable]
public class ReadUncommitedTransactionScopeAttribute : MethodInterceptionAspect
{
    public override void OnInvoke(MethodInterceptionArgs args)
    {
        //declare the transaction options
        var transactionOptions = new TransactionOptions();
        //set it to read uncommited
        transactionOptions.IsolationLevel = IsolationLevel.ReadUncommitted;
        //create the transaction scope, passing our options in
        using (var transactionScope = new TransactionScope(TransactionScopeOption.Required, transactionOptions))
        {
            //declare our context
            using (var scope = new TransactionScope())
            {
                args.Proceed();
                scope.Complete();
            }
        }
    }
}

然后,只要你需要它,

    [ReadUncommitedTransactionScope()]
    public static SomeEntities[] GetSomeEntities()
    {
        using (var context = new MyEntityConnection())
        {
            //any reads we do here will also read uncomitted data
            //...
            //...

        }
    }

能够使用拦截器添加"NOLOCK"也很不错,但是当连接到像Oracle这样的其他数据库系统时也无法工作.

Answer 6

为了解决这个问题,我在数据库上创建了一个视图,并在视图的查询中应用了NOLOCK.然后我将视图视为EF中的表.

Answer 7

随着 EF6 的引入，Microsoft 建议使用 BeginTransaction() 方法。

您可以在 EF6+ 和 EF Core 中使用 BeginTransaction 而不是 TransactionScope

using (var ctx = new ContractDbContext())
using (var transaction = ctx.Database.BeginTransaction(System.Data.IsolationLevel.ReadUncommitted))
{
    //any reads we do here will also read uncommitted data
}