C#•3y ago

Refactor constructor to be used with DI [Answered]

Hello, Is it possible to refactor the following constructor in order to be available for DI without the need to create a new instance?

DatabaseCaller.cs

namespace WebApplication1.Database
{
    public class DatabaseCaller : IDatabaseCaller
    {
        private readonly MyDbContext myDbContext;
        private readonly int someValueFromConfig;
        public DatabaseCaller(MyDbContext myDbContext,
            int someValueFromConfig)
        {
            this.myDbContext = myDbContext;
            this.someValueFromConfig = someValueFromConfig;
        }

        public async Task GetValueFromDb()
        {
            //query the database, code omitted
            await Task.CompletedTask;
        }
    }

    public interface IDatabaseCaller
    {
        Task GetValueFromDb();
    }
}

Program.cs

//... builder.Services.AddScoped<IDatabaseCaller, DatabaseCaller>();

WeatherForecastController.cs

 [ApiController]
    [Route("[controller]")]
    public class WeatherForecastController : ControllerBase
    {

        private readonly AppSettings appSettings;
        private readonly DatabaseCaller databaseCaller;
        private readonly MyDbContext myDbContext;

        public WeatherForecastController(
            IOptions<AppSettings> appSettings,
            MyDbContext myDbContext)
        {
            this.myDbContext = myDbContext;
            this.appSettings = appSettings.Value;
            this.databaseCaller = new DatabaseCaller(myDbContext, this.appSettings.MyValue);
        }

        [HttpGet(Name = "GetWeatherForecast")]
        public async Task GetAsync()
        {
            await databaseCaller.GetValueFromDb();
            await Task.CompletedTask;
        }
    }

11 Replies

nullOP•3y ago

my goal is to inject the database caller, without needing to create a new instance in the WeatherForecastController but I need the ability to retrieve a value from the appsettings

Kouhai•3y ago

Use a factory

nullOP•3y ago

Could you elaborate on that? Any resources or documentation?

Unknown User•3y ago

Message Not Public

Tvde1•3y ago

this may cause issues if you

public Task<Something> GetData()
{
    using var context = CreateContext();
    return context.Stuff.ToListAsync();
}

public Task<Something> GetData()
{
    using var context = CreateContext();
    return context.Stuff.ToListAsync();
}

This could dispose Context before ToListAsync() completes and it may crash stuff

Unknown User•3y ago

Message Not Public

Tvde1•3y ago

yeah specifically awaiting a Task.CompletedTask is useless and adds overhead, but don't always remove async and await and return a Task directly it may cause issues

Unknown User•3y ago

Message Not Public

nullOP•3y ago

to be honest, the code await Task.CompletedTask is just a placeholder, not actually used.

Unknown User•3y ago

Message Not Public

Accord•3y ago

✅ This post has been marked as answered!

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Refactor constructor to be used with DI [Answered]