从实体框架核心5.0+开始，可以简单地覆盖DbContext中的onconfiguration方法一次用于日志记录。这也适用于Single()或Any()查询。

日志记录到调试窗口:

public class ExampleDbContext : DbContext
{
    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
    {
        // using System.Diagnostics;
        optionsBuilder.LogTo(message => Debug.WriteLine(message));
    }
}

登录控制台:

public class ExampleDbContext : DbContext
{
    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
    {
        optionsBuilder.LogTo(Console.WriteLine);
    }
}

更多详细信息，包括日志级别和过滤:https://learn.microsoft.com/en-us/ef/core/logging-events-diagnostics/simple-logging

我的答案是针对EF core的。我参考了这个github问题，以及配置DbContext的文档:

简单的

重写DbContext类(YourCustomDbContext)的onconfiguration方法，如下所示使用ConsoleLoggerProvider;你的查询应该记录到控制台:

public class YourCustomDbContext : DbContext
{
    #region DefineLoggerFactory
    public static readonly LoggerFactory MyLoggerFactory
        = new LoggerFactory(new[] {new ConsoleLoggerProvider((_, __) => true, true)});
    #endregion


    #region RegisterLoggerFactory
    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
        => optionsBuilder
            .UseLoggerFactory(MyLoggerFactory); // Warning: Do not create a new ILoggerFactory instance each time                
    #endregion
}

复杂的

这个Complex case避免覆盖DbContext onconfiguration方法。，这在文档中是不鼓励的:“这种方法不适合测试，除非测试的目标是整个数据库。”

这个复杂的案例使用:

启动类ConfigureServices方法中的IServiceCollection (而不是重写onconfiguration方法;好处是DbContext和你想要使用的ILoggerProvider之间的耦合更松散) ILoggerProvider的实现(而不是使用上面所示的ConsoleLoggerProvider实现;好处是我们的实现展示了我们如何将日志记录到文件(我没有看到一个文件日志记录提供程序与EF核心))

是这样的:

public class Startup

    public void ConfigureServices(IServiceCollection services)
    {
        ...
        var lf = new LoggerFactory();
        lf.AddProvider(new MyLoggerProvider());

        services.AddDbContext<YOUR_DB_CONTEXT>(optionsBuilder => optionsBuilder
                .UseSqlServer(connection_string)
                //Using the LoggerFactory 
                .UseLoggerFactory(lf));
        ...
    }
}

这里是MyLoggerProvider的实现(以及它的MyLogger，它将其日志附加到您可以配置的文件中;您的EF Core查询将出现在文件中。)

public class MyLoggerProvider : ILoggerProvider
{
    public ILogger CreateLogger(string categoryName)
    {
        return new MyLogger();
    }

    public void Dispose()
    { }

    private class MyLogger : ILogger
    {
        public bool IsEnabled(LogLevel logLevel)
        {
            return true;
        }

        public void Log<TState>(LogLevel logLevel, EventId eventId, TState state, Exception exception, Func<TState, Exception, string> formatter)
        {
            File.AppendAllText(@"C:\temp\log.txt", formatter(state, exception));
            Console.WriteLine(formatter(state, exception));
        }

        public IDisposable BeginScope<TState>(TState state)
        {
            return null;
        }
    } 
}

从实体框架核心5.0+开始，可以简单地覆盖DbContext中的onconfiguration方法一次用于日志记录。这也适用于Single()或Any()查询。

日志记录到调试窗口:

public class ExampleDbContext : DbContext
{
    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
    {
        // using System.Diagnostics;
        optionsBuilder.LogTo(message => Debug.WriteLine(message));
    }
}

登录控制台:

public class ExampleDbContext : DbContext
{
    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
    {
        optionsBuilder.LogTo(Console.WriteLine);
    }
}

更多详细信息，包括日志级别和过滤:https://learn.microsoft.com/en-us/ef/core/logging-events-diagnostics/simple-logging

有两种方法:

To view the SQL that will be generated, simply call ToTraceString(). You can add it into your watch window and set a breakpoint to see what the query would be at any given point for any LINQ query. You can attach a tracer to your SQL server of choice, which will show you the final query in all its gory detail. In the case of MySQL, the easiest way to trace the queries is simply to tail the query log with tail -f. You can learn more about MySQL's logging facilities in the official documentation. For SQL Server, the easiest way is to use the included SQL Server profiler.

好吧，目前我正在使用Express分析器，缺点是它只适用于MS SQL Server。你可以在这里找到这个工具:https://expressprofiler.codeplex.com/

Necromancing。 当搜索任何。net框架的解决方案时，这个页面是第一个搜索结果，所以这里作为一个公共服务，它是如何在EntityFrameworkCore(用于。net Core 1和2)中完成的:

var someQuery = (
    from projects in _context.projects
    join issues in _context.issues on projects.Id equals issues.ProjectId into tmpMapp
    from issues in tmpMapp.DefaultIfEmpty()
    select issues
) //.ToList()
;

// string sql = someQuery.ToString();
// string sql = Microsoft.EntityFrameworkCore.IQueryableExtensions.ToSql(someQuery);
// string sql = Microsoft.EntityFrameworkCore.IQueryableExtensions1.ToSql(someQuery);
// using Microsoft.EntityFrameworkCore;
string sql = someQuery.ToSql();
System.Console.WriteLine(sql);

然后这些扩展方法(IQueryableExtensions1用于。net Core 1.0, IQueryableExtensions用于。net Core 2.0):

using System;
using System.Linq;
using System.Reflection;
using Microsoft.EntityFrameworkCore.Internal;
using Microsoft.EntityFrameworkCore.Query;
using Microsoft.EntityFrameworkCore.Query.Internal;
using Microsoft.EntityFrameworkCore.Storage;
using Remotion.Linq.Parsing.Structure;


namespace Microsoft.EntityFrameworkCore
{

    // https://stackoverflow.com/questions/1412863/how-do-i-view-the-sql-generated-by-the-entity-framework
    // http://rion.io/2016/10/19/accessing-entity-framework-core-queries-behind-the-scenes-in-asp-net-core/

    public static class IQueryableExtensions
    {
        private static readonly TypeInfo QueryCompilerTypeInfo = typeof(QueryCompiler).GetTypeInfo();

        private static readonly FieldInfo QueryCompilerField = typeof(EntityQueryProvider).GetTypeInfo().DeclaredFields
            .First(x => x.Name == "_queryCompiler");

        private static readonly PropertyInfo NodeTypeProviderField =
            QueryCompilerTypeInfo.DeclaredProperties.Single(x => x.Name == "NodeTypeProvider");

        private static readonly MethodInfo CreateQueryParserMethod =
            QueryCompilerTypeInfo.DeclaredMethods.First(x => x.Name == "CreateQueryParser");

        private static readonly FieldInfo DataBaseField =
            QueryCompilerTypeInfo.DeclaredFields.Single(x => x.Name == "_database");

        private static readonly PropertyInfo DatabaseDependenciesField =
            typeof(Database).GetTypeInfo().DeclaredProperties.Single(x => x.Name == "Dependencies");

        public static string ToSql<TEntity>(this IQueryable<TEntity> query) where TEntity : class
        {
            if (!(query is EntityQueryable<TEntity>) && !(query is InternalDbSet<TEntity>))
            {
                throw new ArgumentException("Invalid query");
            }

            var queryCompiler = (QueryCompiler) QueryCompilerField.GetValue(query.Provider);
            var nodeTypeProvider = (INodeTypeProvider) NodeTypeProviderField.GetValue(queryCompiler);
            var parser = (IQueryParser) CreateQueryParserMethod.Invoke(queryCompiler, new object[] {nodeTypeProvider});
            var queryModel = parser.GetParsedQuery(query.Expression);
            var database = DataBaseField.GetValue(queryCompiler);
            var databaseDependencies = (DatabaseDependencies) DatabaseDependenciesField.GetValue(database);
            var queryCompilationContext = databaseDependencies.QueryCompilationContextFactory.Create(false);
            var modelVisitor = (RelationalQueryModelVisitor) queryCompilationContext.CreateQueryModelVisitor();
            modelVisitor.CreateQueryExecutor<TEntity>(queryModel);
            var sql = modelVisitor.Queries.First().ToString();

            return sql;
        }
    }



    public class IQueryableExtensions1
    {
        private static readonly TypeInfo QueryCompilerTypeInfo = typeof(QueryCompiler).GetTypeInfo();

        private static readonly FieldInfo QueryCompilerField = typeof(EntityQueryProvider).GetTypeInfo()
            .DeclaredFields
            .First(x => x.Name == "_queryCompiler");

        private static readonly PropertyInfo NodeTypeProviderField =
            QueryCompilerTypeInfo.DeclaredProperties.Single(x => x.Name == "NodeTypeProvider");

        private static readonly MethodInfo CreateQueryParserMethod =
            QueryCompilerTypeInfo.DeclaredMethods.First(x => x.Name == "CreateQueryParser");

        private static readonly FieldInfo DataBaseField =
            QueryCompilerTypeInfo.DeclaredFields.Single(x => x.Name == "_database");

        private static readonly FieldInfo QueryCompilationContextFactoryField = typeof(Database).GetTypeInfo()
            .DeclaredFields.Single(x => x.Name == "_queryCompilationContextFactory");


        public static string ToSql<TEntity>(IQueryable<TEntity> query) where TEntity : class
        {
            if (!(query is EntityQueryable<TEntity>) && !(query is InternalDbSet<TEntity>))
            {
                throw new ArgumentException("Invalid query");
            }

            var queryCompiler = (IQueryCompiler) QueryCompilerField.GetValue(query.Provider);

            var nodeTypeProvider = (INodeTypeProvider) NodeTypeProviderField.GetValue(queryCompiler);
            var parser =
                (IQueryParser) CreateQueryParserMethod.Invoke(queryCompiler, new object[] {nodeTypeProvider});
            var queryModel = parser.GetParsedQuery(query.Expression);
            var database = DataBaseField.GetValue(queryCompiler);
            var queryCompilationContextFactory =
                (IQueryCompilationContextFactory) QueryCompilationContextFactoryField.GetValue(database);
            var queryCompilationContext = queryCompilationContextFactory.Create(false);
            var modelVisitor = (RelationalQueryModelVisitor) queryCompilationContext.CreateQueryModelVisitor();
            modelVisitor.CreateQueryExecutor<TEntity>(queryModel);
            var sql = modelVisitor.Queries.First().ToString();

            return sql;
        }


    }


}