如何在实体框架中指定索引提示? [英] How can I specify an index hint in Entity Framework?

问题描述

select * from table1 with(index=IX_table1_1)

Linq to sql 使用ado.net 实体想写上面的代码.找不到实体，特别是索引提示的使用.

Linq to sql using ado.net entity would like to write the above code. I could not find entity in particular, the use of the index hint.

var querysample = from a in db.table1
select a;

推荐答案

解决方案很简单.让我们添加一个拦截器！！！

Solution is simple. Let's add an Interceptor !!!

    public class HintInterceptor : DbCommandInterceptor
{
    private static readonly Regex _tableAliasRegex = new Regex(@"(?<tableAlias>AS [Extentd+](?! WITH (*HINT*)))", RegexOptions.Multiline | RegexOptions.IgnoreCase);

    [ThreadStatic] public static string HintValue;

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

        HintValue = String.Empty;
    }

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

        HintValue = String.Empty;
    }
}

正则表达式可能会更好，我知道.让我们在 Config 类中注册我们的拦截器

The regex could be better, i know. Let's register our Interceptor in Config class

public class PbsContextConfig : DbConfiguration
{
    public PbsContextConfig()
    {
        this.AddInterceptor(new HintInterceptor());
    }
}

让我们为 DbSet 制作漂亮的提示扩展

Let's make nice Hint Extension for DbSet

public static class HintExtension
{
    public static DbSet<T> WithHint<T>(this DbSet<T> set, string hint) where T : class
    {
        HintInterceptor.HintValue = hint;
        return set;
    }
}

如何使用?

context.Persons.WithHint("INDEX(XI_DOWNTIME_LOCK)").Where( x => x.ID == ....

欢迎修改！

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