如何在 EF Core 3 中启用日志记录？

我正在使用 Entity Framework Core 3 Preview 5 和 ASP.NET Core 3 Preview 5。在 Visual Studio 2019 的调试输出窗口中，我没有从 EF Core 获取任何日志。我阅读了文档，但之后我更加困惑：

1. 根据https://learn.microsoft.com/en-us/dotnet/api/microsoft.entityframeworkcore.dbcontextoptionsbuilder.useloggerfactory?view=efcore-2.1 https://learn.microsoft.com/en-us/dotnet/api/microsoft.entityframeworkcore.dbcontextoptionsbuilder.useloggerfactory?view=efcore-2.1日志记录应该自动设置：

使用“AddDbContext”方法之一时无需调用此方法。 ‘AddDbContext’将确保EF使用的ILoggerFactory是从应用服务提供商处获取的。

但这不是我的经验。

2. 我尝试通过注入来启用日志记录ILoggerFactory to ConfigureServices（我打算然后将其传递给DbContextOptionsBuilder.UseLoggerFactory，但这不再可能了，请参阅https://github.com/aspnet/Announcements/issues/353 https://github.com/aspnet/Announcements/issues/353

那么，如何在 EF Core 3.0 中设置日志记录到调试输出窗口？谢谢！

3.0 RTM 及更高版本的更新：日志级别恢复为信息。查看过滤记录的内容 https://learn.microsoft.com/ef/core/logging-events-diagnostics/extensions-logging?tabs=v3#filtering-and-other-configuration在文档中了解更多详细信息。另请参阅类别列表 https://learn.microsoft.com/ef/core/logging-events-diagnostics/simple-logging#message-categories可用于过滤appsettings.json.

EF Core 日志位于Debuglevel，但主机构建器使用的默认级别是Information。因此，必须手动将日志记录级别设置为Trace or Debug.

默认情况下，此代码不会记录任何 EF 事件：

static async Task Main(string[] args)
{
    var host = Host
        .CreateDefaultBuilder(args)             
        .ConfigureServices((context, services) =>
        {
            var configuration = context.Configuration;
            services.AddDbContext<MyContext>(options =>
                options.UseSqlServer(configuration.GetConnectionString("someConnection")));                    
        })                
        .Build();

    using (var ctx = host.Services.GetRequiredService<MyContext>())
    {
        var cnt = await ctx.Customers.CountAsync();
        Console.WriteLine(cnt);
    }            
}

它只会记录此事件：

info: Microsoft.EntityFrameworkCore.Infrastructure[10403]
  Entity Framework Core 3.0.0-preview6.19304.10 initialized 'ConsolidatorsContext' using provider 'Microsoft.EntityFrameworkCore.SqlServer' with options: None

要记录 EF 事件，我们需要将 EF Core 事件的日志记录级别更改为Trace or Debug通过appsettings.json或代码。例如，将其包含在appsettings.json :

    "Logging": {
        "LogLevel": {
            "Microsoft.EntityFrameworkCore":"Debug"
        }
    },

将记录 EF 事件：

  dbug: Microsoft.EntityFrameworkCore.Infrastructure[10401]
        An 'IServiceProvider' was created for internal use by Entity Framework.
  info: Microsoft.EntityFrameworkCore.Infrastructure[10403]
        Entity Framework Core 3.0.0-preview6.19304.10 initialized 'MyContext' using provider 'Microsoft.EntityFrameworkCore.SqlServer' with options: None
  dbug: Microsoft.EntityFrameworkCore.Database.Connection[20000]
        Opening connection to database 'Customers' on server '10.0.0.216'.
  dbug: Microsoft.EntityFrameworkCore.Database.Connection[20001]
        Opened connection to database 'Customers' on server '10.0.0.216'.
  dbug: Microsoft.EntityFrameworkCore.Database.Command[20100]
        Executing DbCommand [Parameters=[], CommandType='Text', CommandTimeout='30']
        SELECT COUNT(*)
        FROM [Customers] AS [c]
  dbug: Microsoft.EntityFrameworkCore.Database.Command[20101]
        Executed DbCommand (42ms) [Parameters=[], CommandType='Text', CommandTimeout='30']
        SELECT COUNT(*)
        FROM [Customers] AS [c]
  4
  dbug: Microsoft.EntityFrameworkCore.Database.Command[20300]
        A data reader was disposed.
  dbug: Microsoft.EntityFrameworkCore.Database.Connection[20002]
        Closing connection to database 'Customers' on server '10.0.0.216'.
  dbug: Microsoft.EntityFrameworkCore.Database.Connection[20003]
        Closed connection to database 'Customers' on server '10.0.0.216'.
  dbug: Microsoft.EntityFrameworkCore.Infrastructure[10407]
        'MyContext' disposed.