Dependency Injection circular dependency .NET Core 2.0

Question

I want my ApplicationContext constructor to have the UserManager as a parameter, but I am having trouble with dependency injection.

Code:

public class ApplicationContext : IdentityDbContext<ApplicationUser>
{
    private IHttpContextAccessor _contextAccessor { get; set; }
    public ApplicationUser ApplicationUser { get; set; }
    private UserManager<ApplicationUser> _userManager;

    public ApplicationContext(DbContextOptions<ApplicationContext> options, IHttpContextAccessor contextAccessor, UserManager<ApplicationUser> userManager)
        : base(options)
    {
        _contextAccessor = contextAccessor;
        var user = _contextAccessor.HttpContext.User;
        _userManager = userManager;
        ApplicationUser = _userManager.Users.FirstOrDefault(u => u.Id == _userManager.GetUserId(user));
    }
}

And in startup.cs:

public void ConfigureServices(IServiceCollection services)
{
    // Add framework services.
    services.AddDbContext<ApplicationContext>(options =>
        options.UseSqlServer(Configuration.GetConnectionString("DefaultConnection"), b => b.MigrationsAssembly("RCI.App")));

    services.AddIdentity<ApplicationUser, IdentityRole>()
        .AddEntityFrameworkStores<ApplicationContext>()
        .AddDefaultTokenProviders();

    services.AddAuthentication();

    services.AddMvc();

    // Add application services.
    services.AddTransient<IEmailSender, AuthMessageSender>();
    services.AddTransient<ISmsSender, AuthMessageSender>();
    services.AddTransient<IHttpContextAccessor, HttpContextAccessor>();

    services.AddOptions();

}

Error message:

A circular dependency was detected for the service of type 'Microsoft.AspNetCore.Identity.UserManager`1[RCI.App.Models.ApplicationUser]'.

Could anyone point out what I'm doing wrong?

Answer 1

If you don't actually need the UserManager in the constructor, you can store a reference to the IServiceProvider instead:

private IHttpContextAccessor _contextAccessor { get; set; }
public ApplicationUser ApplicationUser { get; set; }
private IServiceProvider _services;

public ApplicationContext(DbContextOptions<ApplicationContext> options,
    IHttpContextAccessor contextAccessor, IServiceProvider services)
    : base(options)
{
    _contextAccessor = contextAccessor;
    var user = _contextAccessor.HttpContext.User;
    _services = services;
}

Then later, when you actually need the ApplicationUser, call e.g. GetRequiredService<ApplicationUser>() (defined in Microsoft.Extensions.DependencyInjection):

var manager = _services.GetRequiredService<UserManager<ApplicationUser>>();
var user = manager.Users.FirstOrDefault(u => u.Id == _userManager.GetUserId(user));

Of course, you can use a Lazy<T> to lazy-load the manager or user the first time and then store a reference to it.

In general, @poke is correct about re-architecting to avoid such circular dependencies, but leaving this answer here in case someone else has a similar problem and refactoring isn't an option.