Cannot get the UserManager class

问题

What I'm trying to do is to add a new admin user and assign it with the admin role. So.. I went to the Startup.cs class in Configure method and wrote the following code:

var context = app.ApplicationServices.GetService<ApplicationDbContext>();

// Getting required parameters in order to get the user manager
var userStore = new UserStore<ApplicationUser>(context);

// Finally! get the user manager!
var userManager = new UserManager<ApplicationUser>(userStore);

However, I get the following error message:

Severity Code Description Project File Line Suppression State Error CS7036 There is no argument given that corresponds to the required formal parameter 'optionsAccessor' of UserManager.UserManager(IUserStore, IOptions, IPasswordHasher, IEnumerable>, IEnumerable>, ILookupNormalizer, IdentityErrorDescriber, IServiceProvider, ILogger>)' FinalProject..NETCoreApp,Version=v1.0 C:\Users\Or Natan\Documents\Visual Studio 2015\Projects\FinalProject\src\FinalProject\Startup.cs 101 Active

This error is killing me here.. obviously I need the userManager in order to create the new user but I just can't initialize this thing.

回答1:

You can use dependency injection to obtain an instance of UserManager. Just add a parameter to the configure method, like this:

public void Configure(IApplicationBuilder app, IHostingEnvironment env, ILoggerFactory loggerFactory, ApplicationDbContext context, UserManager<ApplicationUser> userManager, RoleManager<IdentityRole> roleManager)

Then you can create users and roles. I usually move this code into a static class...

public static class DbInitializer
{
    public static async Task Initialize(ApplicationDbContext context, UserManager<ApplicationUser> userManager, RoleManager<IdentityRole> roleManager)
    {
        // Ensure that the database exists and all pending migrations are applied.
        context.Database.Migrate();

        // Create roles
        string[] roles = new string[] { "UserManager", "StaffManager" };
        foreach (string role in roles)
        {
            if (!await roleManager.RoleExistsAsync(role))
            {
                await roleManager.CreateAsync(new IdentityRole(role));
            }
        }

        // Create admin user
        if (!context.Users.Any())
        {
            await userManager.CreateAsync(new ApplicationUser() { UserName = "info@example.com", Email = "info@example.com" }, "p@ssw0rd");
        }

        // Ensure admin privileges
        ApplicationUser admin = await userManager.FindByEmailAsync("info@example.com");
        foreach (string role in roles)
        {
            await userManager.AddToRoleAsync(admin, role);
        }
    }
}

... and call the method in the Startup.Configure method:

public void Configure(IApplicationBuilder app, IHostingEnvironment env, ILoggerFactory loggerFactory, ApplicationDbContext context, UserManager<ApplicationUser> userManager, RoleManager<IdentityRole> roleManager)
{
    // Code omitted for brevity

    // Create seed data
    DbInitializer.Initialize(context, userManager, roleManager).Wait();
}

In one of the next releases of Entity Framework Core database seeding will be added as a feature.

回答2:

As @JuliusHardt said you can get instance of UserManager via dependency injection. for seeding database first create Extension method like this:

public static class ApplicationDbContextExtensions
{
    public static void EnsureSeedData(this ApplicationDbContext context, UserManager<ApplicationUser> userManager)
    {
        if (!context.Users.Any())
        {
            var result = userManager.CreateAsync(
                new ApplicationUser { UserName = "info@example.com", Email = "info@example.com" },
                "P@ssw0rd").Result;
        }
    }
}

and in Startup class and in Configure method:

if (env.IsDevelopment())
{
    app.UseDeveloperExceptionPage();
    app.UseDatabaseErrorPage();
    app.UseBrowserLink();
    using (var serviceScope = app.ApplicationServices.GetRequiredService<IServiceScopeFactory>().CreateScope())
    {
        // First apply pendding migrations if exist
        serviceScope.ServiceProvider.GetService<ApplicationDbContext>().Database.Migrate();

        // Then call seeder method
        var userManager = serviceScope.ServiceProvider.GetService<UserManager<ApplicationUser>>();
        serviceScope.ServiceProvider.GetService<ApplicationDbContext>().EnsureSeedData(userManager);
    }
}

来源：https://stackoverflow.com/questions/40027388/cannot-get-the-usermanager-class