Property of custom IdentityUser gets populated with data fetched by an unrelated EF context query

Question

I am trying to understand how the following is possible:

In a asp.net core 3.1 web app, I've defined a custom IdentityUser class:

public class ApplicationUser : IdentityUser
{
    public string Name { get; set; }
    public UserSettings Settings { get; set; } = new UserSettings();
}

where UserSettings is:

public class UserSettings
{        
    public int Id { get; set; }
    public string ApiKey { get; set; }
    public string UserId { get; set; }
    public ApplicationUser User { get; set; }
}

The one-to-one relationship is defined using fluent api:

modelBuilder.Entity<UserSettings>()
    .HasOne(e => e.User)
    .WithOne(e => e.Settings)
    .HasForeignKey<UserSettings>(e => e.UserId)
    .IsRequired();            

In the controller with UserManager<ApplicationUser> userManager injected, I understand that:

var user = await userManager.GetUserAsync(User);

does not populate the Settings property with data from the data store. (I wonder why, though, because it does fetch data for the Name property.):

But if I fetch Settings data using the ApplicationDbContext directly:

var user = await userManager.GetUserAsync(User);
var settings = _applicationDbContext.UserSettings.SingleOrDefault(s => s.UserId == user.Id);

the user.Settings property gets populated:

How is this even possible?

Answer 1

Usermanager uses the same context, however, when create the one-to-one relationship, query on foreignkey is not executed.

You need to eager loading the record so that the settings is fetched.

var user = await _userManager.GetUserAsync(User);
var temp = await _dbContext.Users
        .Include(S => S.Settings)
        .AsSplitQuery()
        .IgnoreAutoIncludes()
        .ToListAsync();

That’s why you can fetch the data through using the ApplicationDbContext directly. Data is not separated, but not loaded.

Here is the document https://learn.microsoft.com/en-us/ef/core/querying/related-data/eager