Develop Reference

Initialize object without pushing parameters

I have class with constructor for logging and for access to config:
public class SendEmaiServiceProvider
{
private readonly IConfiguration _config;
private readonly IWebHostEnvironment _env;
private readonly ILogger<SendEmaiServiceProvider> _logger;
private readonly string _fromEmailAddress;
public SendEmaiServiceProvider(IConfiguration config, IWebHostEnvironment env, ILogger<SendEmaiServiceProvider> logger)
{
_config = config;
_env = env;
_logger = logger;
_fromEmailAddress = _config.GetValue<string>("AppSettings:Email:FromEmailAddress");
}
public void SayHi()
{
Console.WriteLine("Hi");
}
}
The question is - How to call method SayHi from another class without pushing logger, env and config?
No I initialize new object with parameters, but I sure that it is wrong:
var sendEmaiServiceProvider = new SendEmaiServiceProvider(_config, _env, _logger);
sendEmaiServiceProvider.SayHi();
I can create an empty constructor but I will not have _fromEmailAddress value.

Looks like this is a netcore website. Assuming so, then:
Create an interface for the dependency.
Register the dependency in Startup.cs
Request the dependency as needed from the netcore DI.
public interface ISendEmaiServiceProvider
{
void SayHi()
}
public class SendEmaiServiceProvider : ISendEmaiServiceProvider
{
public void SayHi() { }
}
Then in Startup.cs:
public void ConfigureServices( IServiceCollection services )
{
services.AddScoped<ISendEmaiServiceProvider, SendEmaiServiceProvider>();
}
Then in the Controller (or wherever else DI is used), request it in the .ctor and all the dependencies for SendEmaiServiceProvider will be filled automatically by DI.
public class HomeController : Controller
{
public readonly ISendEmaiServiceProvider _emailService;
public HomeController( ISendEmaiServiceProvider emailService )
{
_emailService = emailService
}
}
That should get you going.

You should use dependency injection here. Better you create an interface here and resolve your 'SendEmaiServiceProvider' on the startup. And then use the interface instead of creating a new instance for SayHi() method.
public interface YourInterface
{
void SayHi()
}
public class SendEmaiServiceProvider : YourInterface
{
public void SayHi()
{
//your code
}
}
On your startup,
public void ConfigureServices( IServiceCollection services )
{
services.AddScoped<YourInterface, SendEmaiServiceProvider>();
}
On your controller/service,
public class YourController : Controller
{
public readonly YourInterface _emailSenderService;
public HomeController( YourInterface emailSenderService )
{
_emailSenderService = emailSenderService
}
public IActionResult SayHI()
{
_emailSenderService.SayHi()
}
}

C# Asp net core How to call database context outside of controllers

I have a question related to the use of database contexts outside the controller, namely, how to call the database context in a regular class?
To communicate with the database, I use: EF Core
I used options like this:
private readonly MSSQLContext _context;
public BookingController(MSSQLContext context)
{
_context = context;
}
Alternative
using (MSSQLContext context=new MSSQLContext())
{
context.get_Users.ToList();
}
Startup.cs
services.AddDbContext<MSSQLContext>(options =>
options.UseSqlServer(connection));
MSSQLContext.cs
public MSSQLContext()
{
}
public MSSQLContext(DbContextOptions<MSSQLContext> options)
: base(options)
{
}
public DbSet<VIVT_Core_Aud.Models.Core.Logger_Model> Logger_Models { get; set; }
and more tables...

Inject the context into whatever class you need to call into and register that class with the DI framework in your startup class.
For instance,
services.AddTransient<YourType>();
class YourType
{
public YourType(YourDbContext context) { ... }
}

You need to inject context using DI(dependency injection). I am showing you an example of repository pattern. You can search for "Repository pattern EF Core C# examples" will give you lots of examples or blogs to follow. Check here and here
Check out below example..
MyRepository.cs
namespace MyApp.Data.Services
{
public class MyRepository: IMyRepository, IDisposable
{
private MyAppContext _context;
private readonly ILogger<MyRepository> _logger;
public MyRepository(MyAppContext context, ILogger<MyRepository> logger)
{
_context = context ?? throw new ArgumentNullException(nameof(context));
_logger = logger;
}
public IEnumerable<MyTable> GetMyTableData()
{
return _context.MyTable.ToList();
}
}
}
IMyRepository.cs
namespace MyApp.Data.Services
{
public interface IMyRepository
{
//Interface implementation
IEnumerable<MyTable> GetMyTableData();
}
}
Startup.cs of MVC project
services.AddDbContext<MyAppContext>(options =>
options.UseSqlServer(Configuration.GetConnectionString("AppDbConnString")));
//Scope of repository should be based on your project used, I recommend to check lifetime & scope based your project needs.
services.AddScoped<IMyRepository, MyRepository>();
Mycontroller.cs
using MyApp.Data.Services;
namespace MyApp.Controllers
{
public class HomeController : Controller
{
private readonly ILogger<HomeController> _logger;
private readonly IMyRepository _myRepository;
public HomeController(ILogger<HomeController> logger, IMyRepository myRepository)
{
_logger = logger;
_myRepository = myRepository ??
throw new ArgumentNullException(nameof(myRepository));
}
public IActionResult Index()
{
return View();
}
public IActionResult GetAllData()
{
var result = _myRepository.GetMyTableData();
return Json(result);
}
}
}

Asp.Net Core - How to seed data - Object reference not set to an instance of an object

After converted all my tables to start using Guid type in identity columns, I failed to seed data, so I simplified a lot the code to localize the error, and ended with a seeding class as follows:
public class SeedTest
{
private readonly MyDbContext _context;
public SeedTest(MyDbContext context)
{
_context = context;
}
public async Task SeedTest()
{
Values value1 = new Values
{
Id = Guid.Parse("29c48913-1b5c-47b8-g144-08d6d2273deb"),
ValueName = "value 1",
Created = DateTime.Now
};
_context.Values.Add(value1);
await _context.SaveChangesAsync();
}
public SeedTest()
{
}
}
This class is called from another one:
public interface IDatabaseInitializer
{
Task SeedAsync();
}
public class DatabaseInitializer : IDatabaseInitializer
{
public async Task SeedAsync()
{
SeedTest _seedTest = new SeedTest();
await _seedTest.SeedTest();
}
}
which is called from startup.cs
public class Startup
{
public IConfiguration Configuration { get; }
private readonly IHostingEnvironment _hostingEnvironment;
public Startup(IConfiguration configuration, IHostingEnvironment env)
{
Configuration = configuration;
_hostingEnvironment = env;
}
public void ConfigureServices(IServiceCollection services)
{
...
services.AddMyDbContext<MyDbContext>(options =>
options.UseSqlServer("ConnectionStrings:MyCn"));
...
// DB Seeding
services.AddTransient<IDatabaseInitializer, DatabaseInitializer>();
...
...
}
And here is how it is triggered from program.cs
public class Program
{
public static void Main(string[] args)
{
var host = BuildWebHost(args);
using (var scope = host.Services.CreateScope())
{
var services = scope.ServiceProvider;
try
{
var databaseInitializer = services.GetRequiredService<IDatabaseInitializer>();
databaseInitializer.SeedAsync().Wait();
}
catch (Exception ex)
{
var logger = services.GetRequiredService<ILogger<Program>>();
logger.LogCritical(LoggingEvents.INIT_DATABASE, ex, LoggingEvents.INIT_DATABASE.Name);
}
}
host.Run();
}
public static IWebHost BuildWebHost(string[] args) =>
WebHost.CreateDefaultBuilder(args)
.UseStartup<Startup>()
.Build();
}
Unfortunately this implementation didn't seed any data in the database, the unique error I could find is in the logs files, and it says:
System.NullReferenceException: Object reference not set to an instance
of an object. and it points to the last line of SeedTest class.
So what am I doing wrong ?

new SeedTest() does not initialize its _context field. You could use DI on your DatabaseInitializer to instantiate a SeedTest with a MyDbContext.
public class DatabaseInitializer : IDatabaseInitializer
{
private readonly MyDbContext _context;
public DatabaseInitializer(MyDbContext context)
{
_context = context;
}
public async Task SeedAsync()
{
SeedTest _seedTest = new SeedTest(_context);
await _seedTest.SeedTest();
}
}

You are explicitly newing an instance of SeedTest in DatabaseInitialize, while the instance of DatabaseInitialize is being created by the dependency injection service. Register the SeedTest class in the services with the correct scope and let the dependency injection do its thing.
In ConfigureServices add something like
services.AddTransient<SeedTest>();
Modify DatabaseInitializer
public class DatabaseInitializer : IDatabaseInitializer{
private readonly SeedTest _seedTest;
public DatabaseInitializer(SeedTest seedTest)
{
_seedTest = seedTest;
}
public async Task SeedAsync()
{
await _seedTest.SeedTest();
}
}
Remove the parameterless SeedTest constructor and make sure the MyDbContext type registered is what is passed in the other constructor as you have both MyDbContext and DbContext.

You can try this, i have used .net core 2.2 for this sample -
MyDbContext.cs
public class MyDbContext : DbContext
{
public MyDbContext(DbContextOptions<MyDbContext> options) : base(options)
{
Database.EnsureCreated();
}
public DbSet<Values> Values { get; set; }
}
SeedTest.cs
public class SeedTest
{
private readonly MyDbContext _context;
public SeedTest(MyDbContext context)
{
_context = context;
}
public async Task SeedTest1()
{
Values value1 = new Values
{
Id = Guid.Parse("AFE1052A-A694-48AF-AA77-56D2D945DE31"),
ValueName = "value 1",
Created = DateTime.Now
};
_context.Values.Add(value1);
var value = await _context.SaveChangesAsync();
}
public SeedTest()
{
}
}
Service
public interface IDatabaseInitializer
{
Task SeedAsync();
}
public class DatabaseInitializer : IDatabaseInitializer
{
private readonly MyDbContext _cotext;
// Inject DbContext
public DatabaseInitializer(MyDbContext dbContext)
{
_cotext = dbContext;
}
public async Task SeedAsync()
{
// Object with contructor which having DbContext parameter
SeedTest _seedTest = new SeedTest(_cotext);
await _seedTest.SeedTest1();
}
}
startup.cs
services.AddTransient<IDatabaseInitializer, DatabaseInitializer>();
services.AddDbContext<MyDbContext>(option=> option.UseSqlServer("Data Source=localhost;Initial Catalog=StackOverFlow1;Integrated Security=True"));
program.cs
public class Program
{
public static void Main(string[] args)
{
var host = CreateWebHostBuilder(args).Build();
using (var scope = host.Services.CreateScope())
{
var services = scope.ServiceProvider;
try
{
var databaseInitializer = services.GetRequiredService<IDatabaseInitializer>();
databaseInitializer.SeedAsync().Wait();
}
catch (Exception ex)
{
}
}
host.Run();
}
public static IWebHostBuilder CreateWebHostBuilder(string[] args) =>
WebHost.CreateDefaultBuilder(args)
.UseStartup<Startup>();
}
You can read more about seed data.

Repository pattern with multiple databases

I am using repository pattern on EF Core and Autofac in a windows service.
I have a service that needs to connect with the some dozen databases which have the same schema (same dbcontext) but only different data.
How can I achieve this in my service using Autofac? Belo
public class ReportRepository : IReportRepository
{
private readonly ReportDbContext dbContext;
public ReportRepository(ReportDbContext dbContext)
{
this.dbContext = dbContext
}
public SomeModel GetData()
{
return dbContext.SalesData;
}
}
public class ReportService : IReportService
{
private readonly IReportRepository reportRepositoryEUServer;
public ReportService(IReportRepository reportRepositoryEUServer)
{
this.reportRepositoryEUServer = reportRepositoryEUServer
}
public SomeModelDto GenerateReport()
{
var euData = reportRepositoryEUServer.GetData();
// I need to call other servers (e.g LATAM) here and get the data and aggregate them with euData
}
}

Create base context including all settings, dbsets etc:
public abstract class BaseContext : DbContext
{
public BaseContext(DbContextOptions options)
: base(options)
{ }
public DbSet<object> FirstSet { get; set; }
...
}
inherit from BaseContext for both DBs
public class LATAMContext : BaseContext
{
public LATAMContext(DbContextOptions<LATAMContext> options) : base(options)
{
}
}
public class EUContext : BaseContext
{
public EUContext(DbContextOptions<EUContext> options) : base(options)
{
}
}
and register both in Startup.cs
public IServiceProvider ConfigureServices(IServiceCollection services)
{
services.AddDbContext<LATAMContext>(options => options.UseSqlServer(Configuration.GetConnectionString("LATAMConnectionString")));
services.AddDbContext<EUContext>(options => options.UseSqlServer(Configuration.GetConnectionString("EUConnectionString")));
// Autofac
var builder = new ContainerBuilder();
// needed only if you plan to inject ICollection<BaseContext>
builder.RegisterType<LATAMContext>().As<BaseContext>();
builder.RegisterType<EUContext>().As<BaseContext>();
builder.Populate(services);
return new AutofacServiceProvider(builder.Build());
}
add connection strings in appsettings.json
"ConnectionStrings": {
"LATAMConnectionString": "Server=(localdb)\\mssqllocaldb;Database=ContosoUniversity1;Trusted_Connection=True;MultipleActiveResultSets=true",
"EUConnectionString": "Server=(localdb)\\mssqllocaldb;Database=ContosoUniversity1;Trusted_Connection=True;MultipleActiveResultSets=true"
}
and now you can inject both contexts
public class ReportRepository : IReportRepository
{
private readonly LATAMContext latamDbContext;
private readonly EUContext euDbContext;
public ReportRepository(LATAMContext latamDbContext, EUContext euDbContext)
{
this.latamDbContext = latamDbContext;
this.euDbContext = euDbContext;
}
}
or if you plan to inject collection of contexts
public class ReportRepository : IReportRepository
{
private readonly ICollection<BaseContext> dbContexts;
public ReportRepository(ICollection<BaseContext> dbContexts)
{
this.dbContexts = dbContexts;
}
}
to access specific context
var _euContext = dbContexts.FirstOrDefault(x => x is EUContext) as EUContext;
var _latamContext = dbContexts.FirstOrDefault(x => x is LATAMContext) as LATAMContext;

Using DI in AspNET Core

I have a derived class of DbContext, called NavigationContext, that looks like this:
public class NavigationContext : DbContext
{
private readonly IConfiguration _configuration;
public NavigationContext(DbContextOptions<NavigationContext> options, IConfiguration configuration) : base(options)
{
_configuration = configuration;
}
//DbSets here ...
protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
{
if (!optionsBuilder.IsConfigured)
{
optionsBuilder.UseSqlServer(_configuration.GetConnectionString("NavigationLoggingDatabase"));
}
}
}
The Configuration is registered to the DI container in Startup.cs, like this:
public void ConfigureServices(IServiceCollection services)
{
services.AddMvc().SetCompatibilityVersion(CompatibilityVersion.Version_2_1);
services.AddDbContext<NavigationContext>(options => options.UseSqlServer(Configuration.GetConnectionString("NavigationLoggingDatabase")));
services.AddSingleton(_ => Configuration);
}
My question is what do I send to the NavigationContext constructor?
public int Add(TEntity item)
{
using (NavigationContext context = new NavigationContext(_contextOptionsBuilder.Options, ???))
{
context.Set<TEntity>().Add(item);
context.SaveChanges();
return item.Id;
}
}

That's not how you do DI (Dependency Injection). Whenever you see the new keyword for a service, you have to know it's wrong.
First, you don't have to pass in anything to the DbContext, that OnConfiguring override shouldn't be there as you are not using it. This call takes care of that configuration:
services.AddDbContext<NavigationContext>(options => options.UseSqlServer(Configuration.GetConnectionString("NavigationLoggingDatabase")));
Secondly, you don't use using with injected dependencies, so:
public int Add(TEntity item)
{
_context.Set<TEntity>().Add(item);
_context.SaveChanges();
return item.Id;
}
And, for this to work:
public class SomeController : Controller
{
private readonly NavigationContext _context;
public SomeController(NagivationContext context)
{
_context = context;
}
}
And, as a last advice, you should really, really, use the asynchronous versions of the Entity Framework Core methods as much as possible:
public async Task<int> Add(TEntity item)
{
_context.Set<TEntity>().Add(item);
await _context.SaveChangesAsync();
return item.Id;
}

You don't use new NavigationContext(...) at all, you're completely missing the point of dependency injection if you do that. Instead you should be injecting the context into the class that needs it. For example, if you need it directly in your controller, that would look something like this:
public class FunkyController : Controller
{
private readonly NavigationContext _nagivationContext;
public FunkyController(NagivationContext nagivationContext)
{
//Context is injected into the constructor of the controller
_nagivationContext = nagivationContext;
}
public int Add(TEntity item)
{
_nagivationContext.Set<TEntity>().Add(item);
_nagivationContext.SaveChanges();
return item.Id;
}
}