How to merge Identity dbcontext with application context?

I'm not able to read data from Application Identity Users. I'm beginner, any idea? There is no error while compiling. But I cannot add new task.

I get the error while creating a task https://localhost:44312/usertasks/Create

The issue is on GET method but the user lis is not empty

• Results View Expanding the Results View will enumerate the IEnumerable
• [0] {[email protected]} UserTaskTest.Models.ApplicationUser AccessFailedCount 0 int ConcurrencyStamp "785f9a54-e7f1-4e3b-8bad-55165155d631" string Email "[email protected]" string EmailConfirmed false bool ExecutedUserTasks null System.Collections.Generic.ICollection Id "53f416ab-aa1e-465f-9dd4-dc32e11914ae" string LockoutEnabled true bool LockoutEnd null System.DateTimeOffset? NormalizedEmail "[email protected]" string NormalizedUserName "[email protected]" string OwnedUserTasks null System.Collections.Generic.ICollection PasswordHash "AQAAAAEAACcQAAAAEIqkXlzky+4i8BsPl5Z4524B3Dj3u0RZMY2Rf5ch5l22GEMj5m0LsVgeWDAavmVO+g==" string PhoneNumber null string PhoneNumberConfirmed false bool SecurityStamp "698529ad-c47c-40f9-bdf3-c4d946cda86a" string TwoFactorEnabled false bool UserName "[email protected]" string
• [1] {[email protected]} UserTaskTest.Models.ApplicationUser AccessFailedCount 0 int ConcurrencyStamp "1a9064e2-3cc9-4794-9198-81423a5d8cd2" string Email "[email protected]" string EmailConfirmed false bool ExecutedUserTasks null System.Collections.Generic.ICollection Id "970839dc-31be-4966-8f06-e664aca3622c" string LockoutEnabled true bool LockoutEnd null System.DateTimeOffset? NormalizedEmail "[email protected]" string NormalizedUserName "[email protected]" string OwnedUserTasks null System.Collections.Generic.ICollection PasswordHash "AQAAAAEAACcQAAAAEM2KiwEfRDomBNiWXHmEtvwWEodfZDb8eaSADOGP2ZralzlnBDZEMQIsOvTk1nHMcw==" string PhoneNumber null string PhoneNumberConfirmed false bool SecurityStamp "0a829111-88d7-4a8a-b65d-5582cecbe67f" string TwoFactorEnabled false bool UserName "[email protected]" string

System.NullReferenceException: Object reference not set to an instance of an object.
at
Microsoft.AspNetCore.Mvc.Rendering.MultiSelectList.GetListItemsWithValueField()
at Microsoft.AspNetCore.Mvc.Rendering.MultiSelectList.GetListItems()
at Microsoft.AspNetCore.Mvc.Rendering.MultiSelectList.GetEnumerator()

public class UserTask { [Key] [DatabaseGenerated(DatabaseGeneratedOption.Identity)] public int UserTaskID { get; set; } public string Description { get; set; } [ForeignKey("OwnerUserID")] public string TaskOwnerId { get; set; } [ForeignKey("ExecutorUserID")] public string TaskExecutorId { get; set; } public virtual ApplicationUser OwnerUserID { get; set; } public virtual ApplicationUser ExecutorUserID { get; set; } } public class ApplicationUser : IdentityUser { public ICollection<UserTask> OwnedUserTasks { get; set; } public ICollection<UserTask> ExecutedUserTasks { get; set; } } public class ApplicationDbContext : IdentityDbContext<ApplicationUser> { public ApplicationDbContext(DbContextOptions<ApplicationDbContext> options) : base(options) { } public DbSet<UserTask> UserTask { get; set; } protected override void OnModelCreating(ModelBuilder builder) { base.OnModelCreating(builder); builder.Entity<ApplicationUser>() .HasMany(x => x.OwnedUserTasks) .WithOne(x => x.OwnerUserID); builder.Entity<ApplicationUser>() .HasMany(x => x.ExecutedUserTasks) .WithOne(x => x.ExecutorUserID); } } 

Startup.cs

public class Startup { public void ConfigureServices(IServiceCollection services) { services.AddDbContext<ApplicationDbContext>(options => options.UseSqlServer(Configuration.GetConnectionString("DefaultConnection"))); services.AddIdentity<ApplicationUser, IdentityRole>() .AddEntityFrameworkStores<ApplicationDbContext>() .AddDefaultTokenProviders(); // Add application services. services.AddTransient<IEmailSender, EmailSender>(); services.AddMvc(); } } 

UserTaskControler

public class UserTasksController : Controller { private readonly ApplicationDbContext _context; private readonly UserManager<ApplicationUser> _userManager; public UserTasksController(ApplicationDbContext context, UserManager<ApplicationUser> userManager) { _context = context; _userManager = userManager; } public IActionResult Create() { ViewData["TaskOwnerId"] = new SelectList(_userManager.Users.ToList(), "Id", "Name"); ViewData["TaskExecutorId"] = new SelectList(_userManager.Users.ToList(), "Id", "Name"); return View(); } } 

and the view

@model UserTaskTest.Models.UserTask @{ ViewData["Title"] = "Create"; } <h2>Create</h2> <h4>UserTask</h4> <hr /> <div class="row"> <div class="col-md-4"> <form asp-action="Create"> <div asp-validation-summary="ModelOnly" class="text-danger"></div> <div class="form-group"> <label asp-for="Description" class="control-label"></label> <input asp-for="Description" class="form-control" /> <span asp-validation-for="Description" class="text-danger"></span> </div> <div class="form-group"> <label asp-for="TaskOwnerId" class="control-label"></label> <select asp-for="TaskOwnerId" class="form-control" asp-items="ViewBag.TaskOwnerId"></select> </div> <div class="form-group"> <!-- <label asp-for="TaskExecutorId" class="control-label"></label> <select asp-for="TaskExecutorId" class="form-control" asp-items="ViewBag.TaskExecutorId"></select> --> </div> <div class="form-group"> <input type="submit" value="Create" class="btn btn-default" /> </div> </form> </div> </div> <div> <a asp-action="Index">Back to List</a> </div> @section Scripts { @{await Html.RenderPartialAsync("_ValidationScriptsPartial");} }