c# - How can I specify an index hint in Entity Framework?

Question

sql

select * from table1 with(index=IX_table1_1)

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.

linq

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

Answer 1

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;
    }
}

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());
    }
}

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;
    }
}

How to use ?

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

Modifications are welcomed!