.NET MVC Core 2.2 - Can't access user related entity (foreign key)

Question

I am writting my first own app in MVC Core 2 and I am having trouble accessing Estate Entity which have foreign key to User. I have check my db, Estate record is storing userId correctly:

When I try to get context.Estates.FirstOrDefault(m => m.Id == id); I get an Estate entity, but with User == null :

When I try to access it via :

var user = await _userManager.GetUserAsync(User);
var estate = user.Estates.FirstOrDefault(m => m.Id == id);

I get null exception on Estates list. Also trying to save it this way gives me an exception:

var user = await _userManager.GetUserAsync(User);
user.Estates.Add(estate);

However when I type it like that, it saves data correctly in db:

var user = await _userManager.GetUserAsync(User);
estate.User = user;
context.Add(estate);

I have no clue what I did wrong here. I provide my code below, I hope you can give me some tips/advices.

Thats how i build context based on IdentityDbContext:

public class ReaContext : IdentityDbContext<User>
{
    public DbSet<Estate> Estates { get; set; }

    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        base.OnModelCreating(modelBuilder);
    }

    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
    {
        optionsBuilder.UseNpgsql("Server=localhost;Port=5432;Database=rea-dev;User Id=postgres;Password=admin;");
    }

    public ReaContext(DbContextOptions<ReaContext> options)
        : base(options)
    { }

    public ReaContext()
        : base()
    { }
}

My User model:

public class User : IdentityUser
{
    public List<Estate> Estates { get; set; }
}

Estate model:

public class Estate
{
    [Key]
    public int Id { get; set; }
    [MaxLength(100)]
    public string City { get; set; }

    public User User { get; set; }
}

And thats how I add services:

services.AddDbContext<ReaContext>(options => options.UseNpgsql("Server=localhost;Port=5432;Database=rea-dev;User Id=postgres;Password=admin;"));

services.AddIdentity<User, IdentityRole>().AddEntityFrameworkStores<ReaContext>();

I also provide Fluent Api migrations:

    migrationBuilder.CreateTable(
        name: "Estates",
        columns: table => new
        {
            Id = table.Column<int>(nullable: false)
                .Annotation("Npgsql:ValueGenerationStrategy", NpgsqlValueGenerationStrategy.SerialColumn),
            CreationDate = table.Column<DateTime>(nullable: false),
            UpdateDate = table.Column<DateTime>(nullable: false),
            ExpirationDate = table.Column<DateTime>(nullable: false),
            City = table.Column<string>(maxLength: 100, nullable: true),
            UserId = table.Column<string>(nullable: true)
        },
        constraints: table =>
        {
            table.PrimaryKey("PK_Estates", x => x.Id);
            table.ForeignKey(
                name: "FK_Estates_AspNetUsers_UserId",
                column: x => x.UserId,
                principalTable: "AspNetUsers",
                principalColumn: "Id",
                onDelete: ReferentialAction.Restrict);
        });

    migrationBuilder.CreateTable(
        name: "AspNetUsers",
        columns: table => new
        {
            Id = table.Column<string>(nullable: false),
            UserName = table.Column<string>(maxLength: 256, nullable: true),
            NormalizedUserName = table.Column<string>(maxLength: 256, nullable: true),
            Email = table.Column<string>(maxLength: 256, nullable: true),
            NormalizedEmail = table.Column<string>(maxLength: 256, nullable: true),
            EmailConfirmed = table.Column<bool>(nullable: false),
            PasswordHash = table.Column<string>(nullable: true),
            SecurityStamp = table.Column<string>(nullable: true),
            ConcurrencyStamp = table.Column<string>(nullable: true),
            PhoneNumber = table.Column<string>(nullable: true),
            PhoneNumberConfirmed = table.Column<bool>(nullable: false),
            TwoFactorEnabled = table.Column<bool>(nullable: false),
            LockoutEnd = table.Column<DateTimeOffset>(nullable: true),
            LockoutEnabled = table.Column<bool>(nullable: false),
            AccessFailedCount = table.Column<int>(nullable: false)
        },
        constraints: table =>
        {
            table.PrimaryKey("PK_AspNetUsers", x => x.Id);
        });

Answer 1

There are different ways to get related data of a model.

1. Eager loading : means that the related data is loaded from the database as part of the initial query.
2. Explicit loading : means that the related data is explicitly loaded from the database at a later time.
3. Lazy loading : means that the related data is transparently loaded from the database when the navigation property is accessed.

So in your case you can use Eager loading by doing the following:

context.Estates.Include(e => e.User).FirstOrDefault(m => m.Id == id);

---

For more information read this: Loading Related Data .

---

Edit: an example for achieving Eager loading pattern on the IdentityUser :

You can achieve this by either:

1. Injecting UserManager<User> _userManager .
2. Creating your own Service as in Service/Repository Design Pattern .

Let's say you picked the first option. Then you can do the following:

var user = await _userManager.Users
                 .Include(u => u.Estates)
                 .FirstOrDefaultAsync(YOUR_CONDITION);