要将日志保存到PostgreSQL中，您可以使用Serilog的PostgreSQL扩展库。下面是一个使用ASP.NET Core和Serilog将日志保存到PostgreSQL的示例代码：

1. 首先，使用NuGet将以下包添加到您的项目中：

Serilog
Serilog.Sinks.Console
Serilog.Sinks.PostgreSQL

2. 在Program.cs文件中，更新CreateHostBuilder方法以配置Serilog：

using Microsoft.AspNetCore.Hosting;
using Microsoft.Extensions.Hosting;
using Serilog;

public class Program
{
    public static void Main(string[] args)
    {
        Log.Logger = new LoggerConfiguration()
            .WriteTo.Console()
            .WriteTo.PostgreSQL("your_connection_string", "your_table_name")
            .CreateLogger();

        CreateHostBuilder(args).Build().Run();
    }

    public static IHostBuilder CreateHostBuilder(string[] args) =>
        Host.CreateDefaultBuilder(args)
            .UseSerilog()
            .ConfigureWebHostDefaults(webBuilder =>
            {
                webBuilder.UseStartup();
            });
}

3. 在appsettings.json文件中，添加PostgreSQL连接字符串：

{
  "ConnectionStrings": {
    "DefaultConnection": "your_connection_string"
  }
}

4. 在Startup.cs文件中，将Serilog添加到日志服务：

using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;
using Serilog;

public class Startup
{
    public Startup(IConfiguration configuration)
    {
        Configuration = configuration;
    }

    public IConfiguration Configuration { get; }

    public void ConfigureServices(IServiceCollection services)
    {
        services.AddControllers();

        // 添加日志服务
        services.AddLogging(loggingBuilder =>
        {
            loggingBuilder.ClearProviders();
            loggingBuilder.AddSerilog();
        });
    }

    public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
    {
        if (env.IsDevelopment())
        {
            app.UseDeveloperExceptionPage();
        }

        app.UseRouting();

        app.UseEndpoints(endpoints =>
        {
            endpoints.MapControllers();
        });
    }
}

5. 现在，您可以在您的应用程序中使用ILogger接口来记录日志。例如，在控制器中：

using Microsoft.AspNetCore.Mvc;
using Microsoft.Extensions.Logging;

[ApiController]
[Route("[controller]")]
public class WeatherForecastController : ControllerBase
{
    private readonly ILogger _logger;

    public WeatherForecastController(ILogger logger)
    {
        _logger = logger;
    }

    [HttpGet]
    public IEnumerable Get()
    {
        _logger.LogInformation("Getting weather forecast");

        // ...其它代码...

        return weatherForecasts;
    }
}

请确保将your_connection_string替换为您的PostgreSQL连接字符串，your_table_name替换为您要保存日志的表名。

这样，您的日志将会保存到PostgreSQL中。