ASP.NET 核心EF参考回路

Question

I have an ASP.NET Web API project.
Database: PostgreSQL
I have 2 objects - User and Group. It is a many to many relation, thus there are 3 classes - User, Group and UserGroup. The problem comes when I want to get all the groups the user is in - the reference loop. I just need the Groups, not the users in them as well. I'm not sure how to achieve that, for now, I'm just using this:

var user = await _context.Users.Include(u => u.UserGroups).ThenInclude(ug => ug.Group)
                .FirstOrDefaultAsync(u => u.Email == email.ToLower());
            var userGroups = user.UserGroups.Select(ug =>
            {
                var group = ug.Group;
                group.UserGroups = null;
                return group;
            }).ToArray();

To be clear, my problem is not the JSON error, I just don't want those objects to be included.
I thought, that selecting individual columns in the database could help, but I don't think it's a good approach since you'd have to change it every time you change the objects.
EDIT1
What I need to get out is a User with an array of his groups.
EDIT2
The output of the code shown above is this:

{
  "id": "7e445bd2-4257-40ad-bed1-be975e562fa0",
  "registeredAt": "2019-10-06T16:51:39.235955",
  "email": "kozak.vaclav@kobrasoft.cz",
  "firstName": "Vaclav",
  "lastName": "Kozak",
  "locale": "cs-CZ",
  "groups": [
    {
      "id": "7e445bd2-4257-40ad-bed1-be975e562fa0",
      "groupType": 0,
      "userGroups": null
    }
  ]
}

, which is quite what I want, but I'm just looking for some more reasonable solution than mine.

Answer 1

Another way is to search through the association table and select required groups. Lazy loading is not used.

var userGroups = await _context.UserGroup
.Include(x => x.User)
.Include(x => x.Group)
.AsNoTracking()
.Where(x => x.User.Email.ToLower() == e)
.Select(x => x.Group)
.ToListAsync();