Ef-Core-我可以使用什么正则表达式在Db Interceptor中用nolock替换表名

Question

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拦截器来添加With（NOLOCK）提示，以获取所需的查询。您可以在下面找到我之前运行的Db拦截器代码。

   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) ");
    }
} 

在Ef-Core中，我们可以采用几乎相同的方式进行拦截。但是由于表的命名约定发生了变化，因此我无法为新表编写正则表达式。您可以在下面找到新的Ef-Core版本：

public class DbNoLockListener
{
    private static readonly Regex TableAliasRegex = new Regex(@"((?<!\){1,5})AS \[Extent\d+\](?! WITH \(NOLOCK\)))", RegexOptions.Multiline | RegexOptions.IgnoreCase);
    [DiagnosticName("Microsoft.EntityFrameworkCore.Database.Command.CommandExecuting")]
    public void OnCommandExecuting(DbCommand command, DbCommandMethod executeMethod, Guid commandId, Guid connectionId, bool async, DateTimeOffset startTime)
    {
        command.CommandText =
                        TableAliasRegex.Replace(command.CommandText, mt => mt.Groups[0].Value + " WITH (NOLOCK) ");
    }
}

Ef6生成的SQL：

SELECT
    [Extent1].[Id] AS [Extent1Id], 
    [Extent2].[Id] AS [Extent2Id]
    FROM [Advert].[Advert]  AS [Extent1]
    INNER JOIN [Membership].[Members] AS [Extent2] ON [Extent1].[MemberId] = [Extent2].[MemberId]

Ef-Core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]

您也可以查看此github问题以获取更多详细信息。

我想更换 AS [T]与AS [T] WITH（NOLOCK）和 AS [t.Member]与AS [t.Member] WITH（NOLOCK）

我可以使用哪种模式在Ef-Core中执行相同的操作？

Answer 1

这种拦截方法对我来说并不好。IMO的一种更好的方法是挂接到EF Core基础结构上，以覆盖这样的方法的自定义实现来替换SqlServer 的IQuerySqlGenerator服务实现VisitTable：

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

挂接有点复杂，因为我们需要创建并替换“工厂”服务才能替换sql生成器。所有这些的完整代码以及帮助程序扩展方法如下：

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;
        }
    }
}

只需添加一段有意义的代码就可以了，但是这样做的好处是，如果有这样的查询选项，它可以像EF Core那样做。

无论如何，使用上面的代码，您需要从上下文OnConfiguring覆盖中激活它 ：

optionsBuilder.UseCustomSqlServerQuerySqlGenerator();