C# Ef Core-在Db拦截器中，我可以使用什么正则表达式将表名替换为nolock表名

我一直在尝试将我们的EF6项目移植到EF-Core-2.0

在EF6中，我们使用DbNolock拦截器添加和（NOLOCK）提示我们需要的查询。你可以在下面找到我的ex running Db interceptor代码

   public class DbNoLockInterceptor : DbCommandInterceptor
    {
    private static readonly Regex TableAliasRegex = new Regex(@"((?<!\){1,5})AS \[Extent\d+\](?! WITH \(NOLOCK\)))", RegexOptions.Multiline | RegexOptions.IgnoreCase);

    public override void ScalarExecuting(DbCommand command,
        DbCommandInterceptionContext<object> interceptionContext)
    {
        command.CommandText =
            TableAliasRegex.Replace(command.CommandText, mt => mt.Groups[0].Value + " WITH (NOLOCK) ");
    }

    public override void ReaderExecuting(DbCommand command, DbCommandInterceptionContext<DbDataReader> interceptionContext)
    {
        command.CommandText = TableAliasRegex.Replace(command.CommandText,  mt => mt.Groups[0].Value + " WITH (NOLOCK) ");
    }
} 

Ef核心通用SQL：

SELECT 
     [t].[Id]
    ,[t.Member].[Id]
FROM [Advert].[Advert] AS [t]
INNER JOIN [Membership].[Members] AS [t.Member] ON [t].[MemberId] = [t.Member].[MemberId]

你也可以看看

我想换一个 AS[t]与AS[t]与（NOLOCK）和 作为[t.Member]与作为[t.Member]与（NOLOCK）

---

我可以使用哪种模式在Ef Core中执行相同的操作？

通过连接到

DiagnosticsSource

基础设施，可以完成与拦截器等效的操作

首先创建一个拦截器：

public class NoLockInterceptor : IObserver<KeyValuePair<string, object>>
{
    public void OnCompleted()
    {
    }

    public void OnError(Exception error)
    {
    }

    public void OnNext(KeyValuePair<string, object> value)
    {
        if (value.Key == RelationalEventId.CommandExecuting.Name)
        {
            var command = ((CommandEventData)value.Value).Command;

            // Do command.CommandText manipulation here
        }
    }
}

---

这种拦截方法在我看来不太好。IMO的一个更好的方法是连接到EF核心基础设施，用覆盖

VisitTable

方法的自定义实现替换SqlServer的服务实现，如下所示：

public override Expression VisitTable(TableExpression tableExpression)
{
    // base will append schema, table and alias
    var result = base.VisitTable(tableExpression);
    Sql.Append(" WITH (NOLOCK)");
    return result;
}

挂钩有点复杂，因为我们需要创建和替换“工厂”服务，以便能够替换sql生成器。所有这些的完整代码以及辅助扩展方法如下所示：

EF Core 3.x:

using System.Linq.Expressions;
using Microsoft.EntityFrameworkCore.Query;
using Microsoft.EntityFrameworkCore.SqlServer.Query.Sql.Internal;
using Microsoft.EntityFrameworkCore.SqlServer.Query.Internal;
using Microsoft.EntityFrameworkCore.Query.SqlExpressions;

namespace Microsoft.EntityFrameworkCore
{
    public static class CustomDbContextOptionsBuilderExtensions
    {
        public static DbContextOptionsBuilder UseCustomSqlServerQuerySqlGenerator(this DbContextOptionsBuilder optionsBuilder)
        {
            optionsBuilder.ReplaceService<IQuerySqlGeneratorFactory, CustomSqlServerQuerySqlGeneratorFactory>();
            return optionsBuilder;
        }
    }
}

namespace Microsoft.EntityFrameworkCore.SqlServer.Query.Sql.Internal
{
    class CustomSqlServerQuerySqlGeneratorFactory : IQuerySqlGeneratorFactory
    {
        public CustomSqlServerQuerySqlGeneratorFactory(QuerySqlGeneratorDependencies dependencies)
            => Dependencies = dependencies;
        public QuerySqlGeneratorDependencies Dependencies { get; }
        public QuerySqlGenerator Create() => new CustomSqlServerQuerySqlGenerator(Dependencies);
    }

    public class CustomSqlServerQuerySqlGenerator : SqlServerQuerySqlGenerator
    {
        public CustomSqlServerQuerySqlGenerator(QuerySqlGeneratorDependencies dependencies)
            : base(dependencies) { }
        protected override Expression VisitTable(TableExpression tableExpression)
        {
            // base will append schema, table and alias
            var result = base.VisitTable(tableExpression);
            Sql.Append(" WITH (NOLOCK)");
            return result;
        }
    }
}

using System;
using System.Collections.Generic;
using System.Linq;
using System.Linq.Expressions;
using Microsoft.EntityFrameworkCore.Query.Expressions;
using Microsoft.EntityFrameworkCore.Query.Sql;
using Microsoft.EntityFrameworkCore.Storage;
using Microsoft.EntityFrameworkCore.SqlServer.Infrastructure.Internal;
using Microsoft.EntityFrameworkCore.SqlServer.Query.Sql.Internal;

namespace Microsoft.EntityFrameworkCore
{
    public static class CustomDbContextOptionsBuilderExtensions
    {
        public static DbContextOptionsBuilder UseCustomSqlServerQuerySqlGenerator(this DbContextOptionsBuilder optionsBuilder)
        {
            optionsBuilder.ReplaceService<IQuerySqlGeneratorFactory, CustomSqlServerQuerySqlGeneratorFactory>();
            return optionsBuilder;
        }
    }
}

namespace Microsoft.EntityFrameworkCore.SqlServer.Query.Sql.Internal
{
    class CustomSqlServerQuerySqlGeneratorFactory : SqlServerQuerySqlGeneratorFactory
    {
        private readonly ISqlServerOptions sqlServerOptions;
        public CustomSqlServerQuerySqlGeneratorFactory(QuerySqlGeneratorDependencies dependencies, ISqlServerOptions sqlServerOptions)
            : base(dependencies, sqlServerOptions) => this.sqlServerOptions = sqlServerOptions;
        public override IQuerySqlGenerator CreateDefault(SelectExpression selectExpression) =>
            new CustomSqlServerQuerySqlGenerator(Dependencies, selectExpression, sqlServerOptions.RowNumberPagingEnabled);
    }

    public class CustomSqlServerQuerySqlGenerator : SqlServerQuerySqlGenerator
    {
        public CustomSqlServerQuerySqlGenerator(QuerySqlGeneratorDependencies dependencies, SelectExpression selectExpression, bool rowNumberPagingEnabled)
            : base(dependencies, selectExpression, rowNumberPagingEnabled) { }
        public override Expression VisitTable(TableExpression tableExpression)
        {
            // base will append schema, table and alias
            var result = base.VisitTable(tableExpression);
            Sql.Append(" WITH (NOLOCK)");
            return result;
        }
    }
}

---

你到底为什么还在用efcore命令？如果你是的话，为什么还要麻烦升级呢？我只是不明白这有什么意义。@JohnB你能解释一下你的意思吗，因为我不清楚。以上功能不是现成提供的。。。所以我不明白你的意思。这里的正则表达式问题是什么？您希望匹配哪个字符串，不应该匹配哪个字符串，您希望得到什么结果？注意：如果您使用

“$”WITH（NOLOCK）”

而不是

mt=>mt.Groups[0]，则可以大大简化替换过程。值+“WITH（NOLOCK）”

可以通过连接到DiagnosticSource InfrastructureRanks来实现拦截器的等效功能，John。我已经用不同的方式完成了这部分。我的确切问题是：//Do command.CommandText manipulation这里我如何使用nolock操作sql？我想说的是，上述方法可能会降低长期维护的成本，因为您不必处理脆弱的正则表达式code@JohnB好的，如果没有脆弱的正则表达式代码，我们怎么做呢？您的代码没有包含解决方案。我错过了什么吗？嗨，@WiktorStribiżew为什么还不清楚？我只想将所有AS[t]**值更改为**AS[t]，其中（NOLOCK）没有任何EF Core经验，一般来说，您应该使用自己的命名空间，而不是Microsoft的命名空间。@TsahiAsher为什么不在扩展它们时使用Microsoft或System命名空间？尤其是使用EF Core，所有数据库提供程序都使用自定义扩展方法扩展

Microsoft.EntityFrameworkCore

命名空间，如

UseSqlServer

、

UseMySql

和许多其他扩展方法。整个EF核心fluent API体系结构基于自定义扩展方法。想法是让

使用Microsoft.EntityFrameworkCore在你的代码中足以访问所有的代码。好吧，这是一个从中转移出来的。嗨@IvanStoev，这正是我想要的。我已经做了一些测试，它们工作得很好！谢谢你。@IvanStoev非常感谢你为我指明了正确的方向。我在网上的任何地方都找不到这些信息。
DiagnosticListener.AllListeners.Subscribe(new EfGlobalListener());

public override Expression VisitTable(TableExpression tableExpression)
{
    // base will append schema, table and alias
    var result = base.VisitTable(tableExpression);
    Sql.Append(" WITH (NOLOCK)");
    return result;
}

using System.Linq.Expressions;
using Microsoft.EntityFrameworkCore.Query;
using Microsoft.EntityFrameworkCore.SqlServer.Query.Sql.Internal;
using Microsoft.EntityFrameworkCore.SqlServer.Query.Internal;
using Microsoft.EntityFrameworkCore.Query.SqlExpressions;

namespace Microsoft.EntityFrameworkCore
{
    public static class CustomDbContextOptionsBuilderExtensions
    {
        public static DbContextOptionsBuilder UseCustomSqlServerQuerySqlGenerator(this DbContextOptionsBuilder optionsBuilder)
        {
            optionsBuilder.ReplaceService<IQuerySqlGeneratorFactory, CustomSqlServerQuerySqlGeneratorFactory>();
            return optionsBuilder;
        }
    }
}

namespace Microsoft.EntityFrameworkCore.SqlServer.Query.Sql.Internal
{
    class CustomSqlServerQuerySqlGeneratorFactory : IQuerySqlGeneratorFactory
    {
        public CustomSqlServerQuerySqlGeneratorFactory(QuerySqlGeneratorDependencies dependencies)
            => Dependencies = dependencies;
        public QuerySqlGeneratorDependencies Dependencies { get; }
        public QuerySqlGenerator Create() => new CustomSqlServerQuerySqlGenerator(Dependencies);
    }

    public class CustomSqlServerQuerySqlGenerator : SqlServerQuerySqlGenerator
    {
        public CustomSqlServerQuerySqlGenerator(QuerySqlGeneratorDependencies dependencies)
            : base(dependencies) { }
        protected override Expression VisitTable(TableExpression tableExpression)
        {
            // base will append schema, table and alias
            var result = base.VisitTable(tableExpression);
            Sql.Append(" WITH (NOLOCK)");
            return result;
        }
    }
}

using System;
using System.Collections.Generic;
using System.Linq;
using System.Linq.Expressions;
using Microsoft.EntityFrameworkCore.Query.Expressions;
using Microsoft.EntityFrameworkCore.Query.Sql;
using Microsoft.EntityFrameworkCore.Storage;
using Microsoft.EntityFrameworkCore.SqlServer.Infrastructure.Internal;
using Microsoft.EntityFrameworkCore.SqlServer.Query.Sql.Internal;

namespace Microsoft.EntityFrameworkCore
{
    public static class CustomDbContextOptionsBuilderExtensions
    {
        public static DbContextOptionsBuilder UseCustomSqlServerQuerySqlGenerator(this DbContextOptionsBuilder optionsBuilder)
        {
            optionsBuilder.ReplaceService<IQuerySqlGeneratorFactory, CustomSqlServerQuerySqlGeneratorFactory>();
            return optionsBuilder;
        }
    }
}

namespace Microsoft.EntityFrameworkCore.SqlServer.Query.Sql.Internal
{
    class CustomSqlServerQuerySqlGeneratorFactory : SqlServerQuerySqlGeneratorFactory
    {
        private readonly ISqlServerOptions sqlServerOptions;
        public CustomSqlServerQuerySqlGeneratorFactory(QuerySqlGeneratorDependencies dependencies, ISqlServerOptions sqlServerOptions)
            : base(dependencies, sqlServerOptions) => this.sqlServerOptions = sqlServerOptions;
        public override IQuerySqlGenerator CreateDefault(SelectExpression selectExpression) =>
            new CustomSqlServerQuerySqlGenerator(Dependencies, selectExpression, sqlServerOptions.RowNumberPagingEnabled);
    }

    public class CustomSqlServerQuerySqlGenerator : SqlServerQuerySqlGenerator
    {
        public CustomSqlServerQuerySqlGenerator(QuerySqlGeneratorDependencies dependencies, SelectExpression selectExpression, bool rowNumberPagingEnabled)
            : base(dependencies, selectExpression, rowNumberPagingEnabled) { }
        public override Expression VisitTable(TableExpression tableExpression)
        {
            // base will append schema, table and alias
            var result = base.VisitTable(tableExpression);
            Sql.Append(" WITH (NOLOCK)");
            return result;
        }
    }
}

optionsBuilder.UseCustomSqlServerQuerySqlGenerator();