如何在Entity Framework中指定索引提示？

Question

如何在Entity Framework中指定索引提示？

Tal*_*Eri 9 c# linq sql-server entity-framework c#-4.0

SQL

select * from table1 with(index=IX_table1_1)

Run Code Online (Sandbox Code Playgroud)

Linq to sql使用ado.net实体想写上面的代码.我特别找不到实体,使用索引.

LINQ

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

Run Code Online (Sandbox Code Playgroud)

Answer 1

wh1*_*p3r 13

解决方案很简单.让我们添加一个拦截器!

    public class HintInterceptor : DbCommandInterceptor
{
    private static readonly Regex _tableAliasRegex = new Regex(@"(?<tableAlias>AS \[Extent\d+\](?! 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;
    }
}

Run Code Online (Sandbox Code Playgroud)

我知道,正则表达式会更好.让我们在Config类中注册我们的Interceptor

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

Run Code Online (Sandbox Code Playgroud)

让我们为DbSet做一个很好的提示扩展

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

Run Code Online (Sandbox Code Playgroud)

如何使用？

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

Run Code Online (Sandbox Code Playgroud)

欢迎修改!

有趣的想法,但是当我尝试它时,我发现在我的查询之前执行了许多上下文设置查询,并且在第一个上下文设置查询中它清除了HintValue并且从不将它应用于我的查询.此外,因为它正在执行通过ReaderExecuting和ScalarExecuting传递的上下文设置查询,所以"提示"很可能会应用于错误的查询.不知道如何更改代码以使其特定于我的查询,如果我发现如何,我会发布更新. (2认同)

Answer 2

Ted*_*sen 7

添加到 stop-crans 答案，这适用于（我）EF Core 5.0 并支持WITH(INDEX(param))参数。

public class QueryHintInterceptor : DbCommandInterceptor
{
    private static readonly Regex _tableAliasRegex = new Regex(@"(FROM[\s\r\n]+\S+(?:[\s\r\n]+AS[\s\r\n]+[^\s\r\n]+)?)", RegexOptions.Multiline | RegexOptions.IgnoreCase);
    private readonly string _hintPrefix;

    public QueryHintInterceptor(string hintPrefix)
    {
        _hintPrefix = "-- " + hintPrefix;
    }

    public override InterceptionResult<DbDataReader> ReaderExecuting(DbCommand command, CommandEventData eventData, InterceptionResult<DbDataReader> result)
    {
        PatchCommandtext(command);
        return base.ReaderExecuting(command, eventData, result);
    }

    public override ValueTask<InterceptionResult<DbDataReader>> ReaderExecutingAsync(DbCommand command, CommandEventData eventData, InterceptionResult<DbDataReader> result, CancellationToken cancellationToken = default)
    {
        PatchCommandtext(command);
        return base.ReaderExecutingAsync(command, eventData, result, cancellationToken);
    }

    public override InterceptionResult<object> ScalarExecuting(DbCommand command, CommandEventData eventData, InterceptionResult<object> result)
    {
        PatchCommandtext(command);
        return base.ScalarExecuting(command, eventData, result);
    }

    public override ValueTask<InterceptionResult<object>> ScalarExecutingAsync(DbCommand command, CommandEventData eventData, InterceptionResult<object> result, CancellationToken cancellationToken = default)
    {
        PatchCommandtext(command);
        return base.ScalarExecutingAsync(command, eventData, result, cancellationToken);
    }

    private void PatchCommandtext(DbCommand command)
    {
        if (command.CommandText.StartsWith(_hintPrefix, StringComparison.Ordinal))
        {
            int index = command.CommandText.IndexOfAny(Environment.NewLine.ToCharArray(), _hintPrefix.Length);
            command.CommandText = _tableAliasRegex
                .Replace(command.CommandText, "${0} WITH (" + command.CommandText
                .Substring(_hintPrefix.Length, index - _hintPrefix.Length) + ")")
                .Substring(index);
        }
    }
}

public static class QueryHintsDbContextOptionsBuilderExtensions
{
    private const string HintTag = "Use hint: ";
    public static IQueryable<T> WithHint<T>(this IQueryable<T> source, TableHint hint) =>
        source.TagWith(HintTag + hint);
    public static IQueryable<T> WithHint<T>(this IQueryable<T> source, TableHint hint, string param) =>
        source.TagWith(HintTag + hint + " (" + param+")");

    public static DbContextOptionsBuilder AddQueryHints(this DbContextOptionsBuilder builder) =>
        builder.AddInterceptors(new QueryHintInterceptor(HintTag));
}

public enum TableHint
{
    Index,
    KeepIdentity,
    KeepDefaults,
    HoldLock,
    Ignore_Constraints,
    Ignore_Triggers,
    Nolock,
    NoWait,
    PagLock,
    ReadCommitted,
    ReadCommittedLock,
    ReadPast,
    RepeatableRead,
    RowLock,
    Serializable,
    Snapshot,
    TabLock,
    TabLockX,
    UpdLock,
    Xlock
}

Run Code Online (Sandbox Code Playgroud)

Answer 3

Mar*_*ell 6

L2S 和 EF 都不会像定制那样提供对 SQL 的直接支持（索引提示等），尽管使用 L2S 您可以通过ExecuteQuery<T>(...)（使用原始 TSQL）来实现它。如果您需要这种级别的控制，请考虑存储过程或替代 ORM。

这里特别存在的一个问题是查询提示非常特定于平台，但 EF 试图与平台无关。

“如果您需要这种级别的控制，请考虑存储过程或替代 ORM”=> 当然，但不切实际。当你知道事实是这样的时候，为时已晚 (8认同)

Answer 4

sto*_*ran 6

除了 wh1sp3r 的答案之外，请参阅下面的另一个拦截器，它依赖于EF 查询标签而不是线程静态变量：

public class QueryHintInterceptor : DbCommandInterceptor
{
    private static readonly Regex _tableAliasRegex = new Regex("( AS [^ ]+)",
        RegexOptions.Multiline | RegexOptions.IgnoreCase);
    private readonly string _hintPrefix;

    public QueryHintInterceptor(string hintPrefix)
    {
        _hintPrefix = "-- " + hintPrefix;
    }

    public override InterceptionResult<DbDataReader> ReaderExecuting(DbCommand command,
        CommandEventData eventData, InterceptionResult<DbDataReader> result)
    {
        PatchCommandText(command);
        return base.ReaderExecuting(command, eventData, result);
    }

    public override ValueTask<InterceptionResult<DbDataReader>> ReaderExecutingAsync(
        DbCommand command, CommandEventData eventData,
        InterceptionResult<DbDataReader> result,
        CancellationToken cancellationToken = default)
    {
        PatchCommandText(command);
        return base.ReaderExecutingAsync(command, eventData, result, cancellationToken);
    }

    public override InterceptionResult<object> ScalarExecuting(DbCommand command,
        CommandEventData eventData, InterceptionResult<object> result)
    {
        PatchCommandText(command);
        return base.ScalarExecuting(command, eventData, result);
    }

    public override ValueTask<InterceptionResult<object>> ScalarExecutingAsync(
        DbCommand command, CommandEventData eventData, InterceptionResult<object> result,
        CancellationToken cancellationToken = default)
    {
        PatchCommandText(command);
        return base.ScalarExecutingAsync(command, eventData, result, cancellationToken);
    }

    private void PatchCommandText(DbCommand command)
    {
        if (command.CommandText.StartsWith(_hintPrefix, StringComparison.Ordinal))
        {
            int index = command.CommandText.IndexOfAny(Environment.NewLine.ToCharArray(),
                _hintPrefix.Length);
            command.CommandText = _tableAliasRegex
                .Replace(command.CommandText, "${0} WITH (" +  command.CommandText
                    .Substring(_hintPrefix.Length, index - _hintPrefix.Length) + ")")
                .Substring(index);
        }
    }
}

Run Code Online (Sandbox Code Playgroud)

扩展方法：

public static class QueryHintsDbContextOptionsBuilderExtensions
{
    private const string HintTag = "Use hint: ";
    public static IQueryable<T> WithHint<T>(this IQueryable<T> source,
        TableHint hint) =>
        source.TagWith(HintTag + hint);

    public static DbContextOptionsBuilder<TContext> AddQueryHints<TContext>(
        this DbContextOptionsBuilder<TContext> builder)
        where TContext : DbContext =>
        builder.AddInterceptors(new QueryHintInterceptor(HintTag));
}


public enum TableHint
{
    KeepIdentity,
    KeepDefaults,
    HoldLock,
    Ignore_Constraints,
    Ignore_Triggers,
    Nolock,
    NoWait,
    PagLock,
    ReadCommitted,
    ReadCommittedLock,
    ReadPast,
    RepeatableRead,
    RowLock,
    Serializable,
    Snapshot,
    TabLock,
    TabLockX,
    UpdLock,
    Xlock
}

Run Code Online (Sandbox Code Playgroud)

使用示例：

await using var context = new TestDbContext(
    new DbContextOptionsBuilder<TestDbContext>()
        .UseSqlServer("<connection string>")
        .AddQueryHints()
        .LogTo(message => Console.WriteLine("EF: {0}", message))
        .Options);

var result = await context.SomeEntities
    .WithHint(TableHint.TabLock)
    .ToListAsync();

Run Code Online (Sandbox Code Playgroud)

更新

上述自定义 SQL 生成的方式不会产生影响.ToQueryString()，因为命令拦截器在实际 SQL 生成后工作。它会导致测试和日志记录出现问题，例如在 ASP.Net Core 中。因此，另一种解决方案是使用 custom QuerySqlGenerator：

public static class TableHintsDbContextOptionsBuilderExtensions
{
    public static IQueryable<T> WithHint<T>(this IQueryable<T> source,
        TableHint hint) =>
        source.TagWith(hint.ToString());

    public static DbContextOptionsBuilder UseTableHints(
        this DbContextOptionsBuilder builder) =>
        builder.ReplaceService<IQuerySqlGeneratorFactory,
            HintTagSqlServerQuerySqlGeneratorFactory>();
}

class HintTagSqlServerQuerySqlGeneratorFactory : IQuerySqlGeneratorFactory
{
    private readonly QuerySqlGeneratorDependencies dependencies;

    public HintTagSqlServerQuerySqlGeneratorFactory(
        QuerySqlGeneratorDependencies dependencies)
    {
        this.dependencies = dependencies;
    }

    public QuerySqlGenerator Create()
    {
        return new HintTagSqlServerQuerySqlGenerator(dependencies);
    }
}

class HintTagSqlServerQuerySqlGenerator : SqlServerQuerySqlGenerator
{
    private readonly HashSet<TableHint> tableHints = new();

    public HintTagSqlServerQuerySqlGenerator(
        QuerySqlGeneratorDependencies dependencies) :
        base(dependencies)
    {
    }

    protected override void GenerateTagsHeaderComment(
        SelectExpression selectExpression)
    {
        foreach (var tag in selectExpression.Tags)
            if (Enum.TryParse(typeof(TableHint), tag, out var hint))
            {
                tableHints.Add((TableHint)hint!);
                selectExpression.Tags.Remove(tag);
            }

        base.GenerateTagsHeaderComment(selectExpression);
    }

    protected override Expression VisitTable(
        TableExpression tableExpression)
    {
        var result = base.VisitTable(tableExpression);

        if (tableHints.Count > 0)
            Sql.Append($" WITH ({string.Join(", ", tableHints).ToUpperInvariant()})");

        return result;
    }
}

Run Code Online (Sandbox Code Playgroud)

然而，警告说

Microsoft.EntityFrameworkCore.SqlServer.Query.Internal.SqlServerQuerySqlGenerator 是一个内部 API，支持 Entity Framework Core 基础结构，并且不受与公共 API 相同的兼容性标准的约束。它可能会在任何版本中更改或删除，恕不另行通知。

归档时间：	13 年，11 月前
查看次数：	6014 次
最近记录：	9 年，9 月前