Entity Framework Core DbContext and Dependency Injection

Question

I'm building a service application using Web API, .Net Core and EntityFramework Core.

For configuring options in my DbContext I'm using these lines in "ConfigureServices" method in Startup.cs

 var connection = @"Server=ISSQLDEV;Database=EventManagement;Trusted_Connection=True;";
 services.AddDbContext<EMContext>(options => options.UseSqlServer(connection));

I know that if I add the context as a constructor parameter in the controller .Net will inject the context in the constructor.

But this is not the behavior I want. I don't want my web api to know anything about the dbcontext. I have a DataAccess Project with a repository class that handles all CRUD operations.

This means that I just want to say Repository.AddEvent(evt) in my controller and then repository knows how to handle that.

On the other hand, repository uses a simple dependency resolver to get the right "IDataAdapter" implementation. One of those implementations is SQLDataAdapter. This is the point I need my context.

How can I pass my context all the way to this point?

Solution

You can solve this by adding your dbcontext via constructor injection to your classes from your data access layer.

public class Startup
{
    public void ConfigureServices(IServiceCollection services)
    {
        services.AddDbContext<ApplicationDbContext>(o => o.UseSqlServer(myConnStr));
        services.AddScoped<Repository>(); // 'scoped' in ASP.NET means "per HTTP request"
    }
}

public class MvcController
{
    private Repository repo;
    public MvcController(Repository repo)
    {
        this.repo = repo;
    }

    [HttpPost]
    public void SomeEndpoint()
    {
        this.repo.AddFoo(new Foo());
    }
}

public class Repository
{
    private DbContext db;
    public Repository(ApplicationDbContext db)
    {
        this.db = db;
    }

    public void AddFoo(Foo obj)
    {
        this.db.Set<Foo>().Add(obj);
        this.db.SaveChanges();
    }
}

If you want to further customize how your DbContext is injected into your DI container, I suggest you look at what .AddDbContext is actually doing. See https://github.com/aspnet/EntityFramework/blob/1.0.0/src/Microsoft.EntityFrameworkCore/EntityFrameworkServiceCollectionExtensions.cs#L142-L158