ASP.NET Core: Dependency Injection for DB CF Migrations

Question

ASP.NET Core: Dependency Injection for DB CF Migrations

.net-core asp.net-core-mvc c# dependency-injection entity-framework-core

Question

I'm using dependency injection to register my DbContext in the controller of a ASP.NET MVC Core Application like this:

public void ConfigureServices(IServiceCollection services) {
    return new MyContext(connectionString); }
        services.AddScoped<IMyContext, MyContext>((serviceProdiver) => {
            return new MyContext(Configuration["ConnectionStrings:MyContext"]); 
        });
        services.AddMvc();
    }

This works well. But now I want to use Migrations like Add-Migration Initial -Context MyContext which requires a parameterless constructor. But this would destroy the DI pattern because I would need to fallback to singleton pattern from classic ASP.NET MVC like the following:

public class MyContext:MySqlDbContext, IMyContext {
    public MyContext() : base(Startup.Configuration["ConnectionStrings:MyContext"] {
    }
}

I like to avoid this to consequently use DI in my new ASP.NET Core project. Is this possible using database-migrations or isn't the migration-tool updated yet for DI so that there is no alternative to use the old singleton pattern here?

Lion

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Andrew · Accepted Answer · 8/27/2016 9:44:00 PM

Wow, you did very big mistake. You need not to add some your configuration to MyContext, because it's autogenerated file. What have you to do ? You have to add some your configuration file for example RegisterServices or it will be extension. For example

public static class ServiceCollectionExtensions
{
 public static IServiceCollection RegisterServices(
    this IServiceCollection services)
{
    services.AddTransient<ICountryService, CountryService>();
    // and a lot more Services

    return services;
}

}

And after that you have to Register this your configuration file in ConfigureServices, for example

public void ConfigureServices(IServiceCollection services)
{
// Add framework services.
services.AddMvc();

services.RegisterServices();
}

Finally, you can use Services or Repositories

public class HomeController : Controller 
{ 
private readonly ICountryService _countryService; 

 public HomeController(ICountryService countryService) 
 { 
    _countryService = countryService; 
 } 
// â€¦ 
}

Or, at the moment new in ASP.NET Core MVC is, that we can also inject this service into a MVC view. The following line defines the injection in a Razor view:

@inject DiViews.Services.ICountryService CountryService;

The first part after the @inject directive defines the interface. The second part is the name of the variable which holds our instance.

To inject a service globally into all Views, add this line to the _ViewImports.cshtml. In a complete new ASP.NET Core project, there is already a global injection defined for ApplicationInsights:

@inject Microsoft.ApplicationInsights.Extensibility.TelemetryConfiguration TelemetryConfiguration

We are now able to use the instance in our view:

@if (countryService.All().Any()) 
{ 
 <ul> 
    @foreach (var country in CountryService.All().OrderBy(x => x.Name)) 
    { 
        <p>@country.Name (@country.Code)</p> 
    } 
 </ul> 
 }

We can also use this service to fill select fields with the list of countries:

@Html.DropDownList("Coutries", CountryService.All() 
.OrderBy(x => x.Name) 
.Select(x => new SelectListItem 
{ 
    Text = x.Name, 
    Value = x.Code 
}))

I hope, it was helpful for you

ASP.NET Core: Dependency Injection for DB CF Migrations

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