Where to register the context with dependency injection

Question

According to this tutorial I should:

Register your context with dependency injection

The Tutorial describes that I should locate the method ConfigureServices() and put in there the code advised.

Here's my startup.cs:

using Microsoft.Owin;
using Owin;

[assembly: OwinStartupAttribute(typeof(MyProject.Startup))]
namespace MyProject
{
    public partial class Startup
    {
        public void Configuration(IAppBuilder app)
        {
            ConfigureAuth(app);
        }
    }
}

so I don't know where to correctly put the code.

Because the project isn't compatible with .net core 2.1, it was needed to change Project->Property to .Net Framework 4.6.1 and install packages Microsoft.EntityFrameworkCore.SqlServer and Microsoft.EntityFrameworkCore.Tools

I tried to add the dependency injection to global.asax.cs file as follows:

protected void Application_Start()
        {
            var services = new ServiceCollection();
            ConfigureServices(services);
            AreaRegistration.RegisterAllAreas();
            FilterConfig.RegisterGlobalFilters(GlobalFilters.Filters);
            RouteConfig.RegisterRoutes(RouteTable.Routes);
            BundleConfig.RegisterBundles(BundleTable.Bundles);
}

private void ConfigureServices(IServiceCollection services)
    {
        var connection = @"Server=(localdb)\mssqllocaldb;Database=Blogging;Trusted_Connection=True;ConnectRetryCount=0";
        services.AddDbContext<BloggingContext>(options => options.UseSqlServer(connection));
    }

I succeeded with the step and created the controller and it works, but I haven't chosen the right context (BloggingContext), so it created second database. So, I need to create a controller with BloggingContext, do you know how?

Answer 1

The version of the shown startup and the tutorial are in conflict with each other.

If this if for an Asp.Net Core MVC application then you can add the method your self. Startup class is part of the convention.

public partial class Startup {
    //...

    // This method gets called by the runtime. Use this method to add services to the container.
    public void ConfigureServices(IServiceCollection services)
    {
         //...
    }
}

Reference App startup in ASP.NET Core

The ConfigureServices method

The ConfigureServices method is:

• Optional.
• Called by the host before the Configure method to configure the app's services.
• Where configuration options are set by convention.

---

If however you are trying to use .Net Core technologies in an Asp.Net MVC 5+ (which is what the GitHub project targets) then you will need to modify your approach to adapt to using .Net Core Dependency Injection with a non core platform.

First you will need a IDependencyResolver which is the DI framework used by that version of Asp.Net MVC, and a way to replace the default resolver with your own.

public sealed class CoreDependencyResolver : System.Web.Mvc.IDependencyResolver {
    private readonly System.Web.Mvc.IDependencyResolver mvcInnerResolver;
    private readonly IServiceProvider serviceProvider;

    public CoreDependencyResolver(IServiceProvider serviceProvider, System.Web.Mvc.IDependencyResolver dependencyResolver) {
        this.serviceProvider = serviceProvider;
        mvcInnerResolver = dependencyResolver;
    }

    public object GetService(Type serviceType) {
        object result = this.serviceProvider.GetService(serviceType);
        if (result == null && mvcInnerResolver != null)
            result = mvcInnerResolver.GetService(serviceType);
        return result;
    }

    public IEnumerable<object> GetServices(Type serviceType) {
        IEnumerable<object> result = this.serviceProvider.GetServices(serviceType);
        if (result == null && mvcInnerResolver != null)
            result = mvcInnerResolver.GetServices(serviceType);
        return result ?? new object[0];
    }
}

With the custom resolver in place, you can now configure the application to use it.

Using your current example as a starting point (review comments)

protected void Application_Start() {
    var services = new ServiceCollection();
    ConfigureServices(services);
    //build service provider
    IServiceProvider provider = services.BuildServiceProvider();
    //Get the current resolver used by MVC
    var current = DependencyResolver.Current;
    //use that and the provider to create your custom resolver
    var resolver = new CoreDependencyResolver(provider, current);
    //now set the MVC framework to use the resolver that wraps the service provider
    //that was created from .Net Core Dependency Injection framework.
    DependencyResolver.SetResolver(resolver);
    //...

    AreaRegistration.RegisterAllAreas();
    FilterConfig.RegisterGlobalFilters(GlobalFilters.Filters);
    RouteConfig.RegisterRoutes(RouteTable.Routes);
    BundleConfig.RegisterBundles(BundleTable.Bundles);
}

private void ConfigureServices(IServiceCollection services) {
    //... omitted for brevity (register dependencies as normal)
}

Answer 2

Here I am using Oracle, but you could do the same with SQL Server...

 public void ConfigureServices(IServiceCollection services)
 {

        services.AddEntityFrameworkOracle()
            .AddDbContext<OracleDbContext>(builder => builder.UseOracle(Configuration["Data:OracleDbContext"]),ServiceLifetime.Scoped)
            .AddDbContext<AppsDbContext>(option => option.UseOracle(Configuration["Data:AppsDbConnection:ConnectionString"]), ServiceLifetime.Scoped);

Then in my appsettings.json, I include the connection strings...

"Data": {
"OracleDbContext": "your connection string" },
"AppsDbContext": "your connection string" }
 }

Answer 3

It appears you're using .Net Framework, rather than .Net Core.

2 simple ideas here:

• Injecting DbContext into service layer: this layer will be class Library for .Net Framework or (use .Net Standard Class library if your platform is .Net Core). This thread shows you how to perform it: Injecting DbContext into service layer
• use Ninject as dependency injector if you're on .Net Framework platform. This thread shows a good example: How to handle DBContext when using Ninject

Answer 4

Whilst using .NET Core tooling with full framework works quite well, if you have to use MVC5 and full framework I would not try to work it that way round.

There are many .NET 4.6.1 dependency injection frameworks, in this example I will use Autofac.

• Install the NuGet packages Autofac and Autofac.Mvc5.
• Add an AutofacRegistration.cs class to the App_Start folder
• In the Application_Start() method in Global.asax add the line AutofacRegistration.BuildContainer();

Your AutofacRegistration class is where you wire up all your dependencies for dependency injection. The full docs are here https://autofaccn.readthedocs.io/en/latest/integration/mvc.html

public class AutofacRegistration
{
    public static void BuildContainer()
    {
        var builder = new ContainerBuilder();

        // Register your MVC controllers
        builder.RegisterControllers(typeof(MvcApplication).Assembly);

        // Now grab your connection string and wire up your db context
        var conn = ConfigurationManager.ConnectionStrings["BloggingContext"];
        builder.Register(c => new BloggingContext(conn));

        // You can register any other dependencies here

        // Set the dependency resolver to be Autofac.
        var container = builder.Build();
        DependencyResolver.SetResolver(new AutofacDependencyResolver(container));
    }
}

This is assuming your BloggingContext has a constructor that takes the connection string as a parameter and passes it to the base class. Something like

public class BloggingContext : DbContext
{
    public BloggingContext(string connectionString) : base(connectionString)
    {
    }
}

There is loads more in the documentation about scope etc that is worth reading but this should be the nuts and bolts of it.