EF 6参数嗅探

I like VahidN's solution, do up vote him, but I want more control of when it happens. It turns out that DB Interceptors are very global, and I only wanted this to happen on specific contexts in specific scenarios.

Here we are setting the ground work to also support adding other query hints, that could be turned on and off as desired.

Since I often expose the method for passing a connection string, I also included support for that.

Below would give your context a flag to enable/disable the hint programatically, by extending the partial class EF generates. We also threw the small piece of reused code in the Interceptor into its own method.

Small Interface

public interface IQueryHintable
{
    bool HintWithRecompile { get; set; }
}

DB Command Interceptor

public class OptionHintDbCommandInterceptor : IDbCommandInterceptor
{
    public void NonQueryExecuting(DbCommand command, DbCommandInterceptionContext<Int32> interceptionContext)
    {
        AddHints(command, interceptionContext);
    }

    public void NonQueryExecuted(DbCommand command, DbCommandInterceptionContext<int> interceptionContext)
    {
    }

    public void ReaderExecuted(DbCommand command, DbCommandInterceptionContext<DbDataReader> interceptionContext)
    {
    }

    public void ReaderExecuting(DbCommand command, DbCommandInterceptionContext<DbDataReader> interceptionContext)
    {
        AddHints(command, interceptionContext);
    }

    public void ScalarExecuted(DbCommand command, DbCommandInterceptionContext<object> interceptionContext)
    {
    }

    public void ScalarExecuting(DbCommand command, DbCommandInterceptionContext<object> interceptionContext)
    {
        AddHints(command, interceptionContext);
    }

    private static void AddHints<T>(DbCommand command, DbCommandInterceptionContext<T> interceptionContext)
    {
        var context = interceptionContext.DbContexts.FirstOrDefault();
        if (context is IQueryHintable)
        {
            var hints = (IQueryHintable)context;

            if (hints.HintWithRecompile)
            {
                addRecompileQueryHint(command);
            }
        }
    }

    private static void addRecompileQueryHint(IDbCommand command)
    {
        if (command.CommandType != CommandType.Text || !(command is SqlCommand))
            return;

        if (command.CommandText.StartsWith("select", StringComparison.OrdinalIgnoreCase) && !command.CommandText.Contains("option(recompile)"))
        {
            command.CommandText = command.CommandText + " option(recompile)";
        }
    }
}

Extending Entity Context to Add IQueryHintable

public partial class SomeEntities : DbContext, IQueryHintable
{
    public bool HintWithRecompile { get; set; }

    public SomeEntities (string connectionString, bool hintWithRecompile) : base(connectionString)
    {
        HintWithRecompile = hintWithRecompile;
    }

    public SomeEntities (bool hintWithRecompile) : base()
    {
        HintWithRecompile = hintWithRecompile;
    }

    public SomeEntities (string connectionString) : base(connectionString)
    {
    }

}

Register DB Command Interceptor (global.asax)

    DbInterception.Add(new OptionHintDbCommandInterceptor());

Enable context wide

    using(var db = new SomeEntities(hintWithRecompile: true) )
    {
    }

打开或关闭

    db.HintWithRecompile = true;
    // Do Something
    db.HintWithRecompile = false;

我将其称为HintWithRecompile，是因为您可能还想实现HintOptimizeForUnknown或其他查询提示。

在DB上执行它们之前,可以使用EF6的拦截功能来操作其内部SQL命令,例如option(recompile)在命令末尾添加:

public class OptionRecompileHintDbCommandInterceptor : IDbCommandInterceptor
{
    public void NonQueryExecuting(DbCommand command, DbCommandInterceptionContext<Int32> interceptionContext)
    {
    }

    public void NonQueryExecuted(DbCommand command, DbCommandInterceptionContext<int> interceptionContext)
    {
    }

    public void ReaderExecuted(DbCommand command, DbCommandInterceptionContext<DbDataReader> interceptionContext)
    {
    }

    public void ReaderExecuting(DbCommand command, DbCommandInterceptionContext<DbDataReader> interceptionContext)
    {
        addQueryHint(command);
    }

    public void ScalarExecuted(DbCommand command, DbCommandInterceptionContext<object> interceptionContext)
    {
    }

    public void ScalarExecuting(DbCommand command, DbCommandInterceptionContext<object> interceptionContext)
    {
        addQueryHint(command);
    }

    private static void addQueryHint(IDbCommand command)
    {
        if (command.CommandType != CommandType.Text || !(command is SqlCommand))
            return;

        if (command.CommandText.StartsWith("select", StringComparison.OrdinalIgnoreCase) && !command.CommandText.Contains("option(recompile)"))
        {
            command.CommandText = command.CommandText + " option(recompile)";
        }
    }
}

要使用它,请在应用程序的开头添加以下行:

DbInterception.Add(new OptionRecompileHintDbCommandInterceptor());