EF Core: many-to-many query - sql

Question

I am trying to return all items in UserDTO from a User given a particular Team. The below code only returns the UserId (since that is what contained in TeamUser). Can this be done in a straightforward way? Or do I have to perform a second lookup on Users once the UserId's are given?
public class User
{
public long UserId { get; set; }
public string? Name { get; set; }
[Required]
[EmailAddress]
public string? Email { get; set; } = default!;
[Required]
public string? CreatedDate { get; set; }
/* relationships */
public virtual ICollection<TeamUser>? Teams { get; set; } //many Teams to many Users
}
public class Team
{
public long TeamId { get; set; }
[Required]
public string? Name { get; set; }
[Required]
public string? CreatedDate { get; set; }
/* relationships to User */
public virtual ICollection<TeamUser>? Users { get; set; } //many Users to many Teams
}
public class UserDTO
{
public long UserId { get; set; }
public string? Name { get; set; }
[Required]
[EmailAddress]
public string? Email { get; set; } = default!;
}
public class TeamUser
{
public long TeamId { get; set; }
public Team? Team { get; set; }
public long UserId { get; set; }
public User? User { get; set; }
}
[HttpGet]
public async Task<ActionResult<IEnumerable<UserDTO>>> GetUsers(long? userId, long? teamId)
{
if(teamId == null)
{
return await _context.Users.Select(x => UserToDTO(x)).ToListAsync();
}
else
{
// get users given teamId
return await _context.TeamUsers
.Include(u => u.User)
.Where(t => t.TeamId == teamId)
.Select(pt => new UserDTO
{
UserId = pt.UserId
})
.ToListAsync();
}

Answer 1

EF Core introduced the new ThenInclude() extension method to load multiple levels of related entities.
As EF Core won't load related properties automatically, so you'll need to explicitly do this, but something like the following should do the trick:
var result = context.Begrip
.Include(x => x.Categories)
.ThenInclude(x => x.category);
Note, intellisense doesn't always work on .ThenInclude at the moment, but the code should still compile even if it gets a red underline.
If you're returning this to the view or an API, you'll likely want to map it to a DTO so you don't have to deal with .Categories[0].category.Name etc.