C# – Logging in .NET Core

By | 01/09/2020

In this post, we will see how to add Logging in the project Api.Orders created in the post: Web API – How to use Polly library with Ocelot.
Logging is a built-in feature of ASP.NET Core and .NET Core Work Services and it is provided as part of the Microsoft.Extensions.Logging library.
For more information: Microsoft Web Site

First of all, we open the Api.Orders project and we install the Serilog.Extensions.Logging.File library that it will allow us to write the log in a file.
Then, we open the Startup file and we define the name of the log file:

[STARTUP.CS]

public void Configure(IApplicationBuilder app, IWebHostEnvironment env, ILoggerFactory loggerFactory)
{
     // Definition of the file where we will save the log.
     loggerFactory.AddFile($"Logs/Orders-{DateTime.Now.ToLongDateString()}.txt");

     if (env.IsDevelopment())
     {
          app.UseDeveloperExceptionPage();
     }

     app.UseRouting();

     app.UseAuthorization();

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



Finally, we will add Logging in the method GetOrdersAsync of CoreOrders:

[COREORDERS.CS]

using Api.Orders.Core.Interfaces;
using Api.Orders.Db;
using Microsoft.Extensions.Logging;
using System;
using System.Collections.Generic;
using System.Threading.Tasks;

namespace Api.Orders.Core.Providers
{
    public class CoreOrder : ICoreOrder
    {
        // Definition of Logger
        private readonly ILogger<CoreOrder> logger;
        private readonly IBooksService booksService;
        private readonly ICustomersService customersService;

        public CoreOrder(IBooksService inputBooksService, ICustomersService inputCustomersService, ILogger<CoreOrder> inputLogger)
        {
            booksService = inputBooksService;
            customersService = inputCustomersService;
            // With dependency injection, we create the logger<CoreOrder> object  
            logger = inputLogger;
        }
        
        public async Task<(bool IsSuccess, IEnumerable<Order> Orders, string ErrorMessage)> GetOrdersAsync()
        {
            List<Order> lstOrder = new List<Order>();

            try
            {
                for (int i = 1; i < 6; i++)
                {
                    var objOrder = new Order();
                    objOrder.Id = i;
                    objOrder.OrderDate = DateTime.Now.AddDays(-i);
                    var resultCustomerService = await customersService.GetCustomer(i);
                    if (resultCustomerService.IsSuccess)
                    {
                        objOrder.EmailCustomer = resultCustomerService.ObjCustomer.Email;
                    }

                    var lstOrderItems = new List<OrderItem>();
                    for (int y = i; y < (i + 3); y++)
                    {
                        var orderItem = new OrderItem();
                        var resultBookService = await booksService.GetBook(y);
                        if (resultBookService.IsSuccess)
                        {
                            // we add a log to know the workflow of the app
                            logger?.LogInformation($"Called with success BookService using id:{y}");
                            orderItem.BookTitle = resultBookService.ObjBook.Title;
                            orderItem.Price = resultBookService.ObjBook.Price;
                        }
                        else
                        {
                            // we add a log to know the workflow of the app
                            logger?.LogInformation($"BookService didn't give result. Id:{y}");
                            orderItem.BookTitle = "Book information is not available";
                            orderItem.Price = 0;
                        }

                        orderItem.Quantity = y;
                        objOrder.Total = objOrder.Total + (orderItem.Price * orderItem.Quantity);

                        lstOrderItems.Add(orderItem);
                    }

                    objOrder.Books = new List<OrderItem>();
                    objOrder.Books.AddRange(lstOrderItems);

                    lstOrder.Add(objOrder);
                }

                return (true, lstOrder, null);
            }
            catch(Exception ex)
            {
                // we add a log in case of exception
                logger?.LogError(ex.ToString());
                return (false, null, ex.Message);
            }
        }
    }
}



We have done and, if we run the application, we will be able to read the log file:



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