Populating list of users from IdentityDbContext

Question

I'm trying to populate a dropdown list in my Razor page. To do this, I created a view model that will have a list of users. The list of users needs to be populated from IdentityDbContext.

I'm going through all the examples posted by other users and the issue I'm having is defining the correct variables.

Startup.cs

services.AddDbContextPool<AppDbContext>(options => options.UseSqlServer(_config.GetConnectionString("DefaultConnection")));

AppDbContext.cs

public class AppDbContext : IdentityDbContext<ApplicationUser>
{
    public AppDbContext(DbContextOptions<AppDbContext> options)
        : base(options)
    {
    }
}

ProcessCreateViewModel.cs

public IEnumerable<ApplicationUser> Users { get; set; }
public string User { get; set; }

ProcessController.cs

public IActionResult CreateProcess()
{
    var context = new AppDbContext();
    var processCreateViewModel = new ProcessCreateViewModel()
    {
        Users = context.Users.ToList()
    };            
    return View(processCreateViewModel);
}

CreateProcess.cshtml

<div class="form-group">
   @Html.LabelFor(x => Model.User, htmlAttributes: new { @class = "control-label col-md-2" })
   <div class="col-md-5">
      @Html.DropDownListFor(x => Model.User, new SelectList(Model.Users, "Value", "Text"), htmlAttributes: new { @class = "form-control", id = "ApplicationUser" })
      @Html.ValidationMessageFor(x => x.User, "", new { @class = "text-danger" })
    </div>
</div>

The issue I'm experiencing is that the line in ProcessController.cs, var context = new AppDbContext();

return an error:

There is no argument given that corresponds to the required formal parameter 'options'

I have no idea how to fix or change my approach to get the user loaded into a list on my ViewModel so that I can use it in a dropdown list on my page.

Answer 1

You need to add it like this: services.AddDbContextPool<AppDbContext>(options => options.UseSqlServer(_config.GetConnectionString("DefaultConnection")));

As well why are you initializing a new isntance of DB context, you need to dependecy inject the Db context, as you are initializing it for DI with this line services.AddDbContextPool<AppDbContext>(options => options.UseSqlServer(_config.GetConnectionString("DefaultConnection")));, then everything should be fine, for example:

public class YourController {

public YourController (YourDbContext context){
//.. Assign here and then reuse in controller end points
}

}

Otherwise you are trying to initialize the DBContext yourself and the DbContext as it says does not have a default constructor to address to.