✅ EF Core include only one property of collection

    var query = db.Projects
      .Include(static project => project.Owner)
      .Include(static project => project.OwnerGroup)
      .Where(p => p.ParentProjectId == null || p.ParentProjectId == -1)
      .Where(p => caller.IsAdmin || p.Owner!.Username == caller.Username || p.OwnerGroup!.Users.Contains(user));

    query = query  
      .Include(static project => project.SubProjects)
      .ThenInclude(static subProject => subProject.ProjectId);

[Index(nameof(Name), IsUnique = true)]
public class Project
{
  [Key]
  [Required]
  [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
  public int ProjectId { get; set; }

  [Required]
  [StringLength(100, MinimumLength = 1)]
  public string Name { get; set; } = "";

  [StringLength(200)]
  public string Description { get; set; } = "";

  public User? Owner { get; set; }
  public int? OwnerId { get; set; }

  public UserGroup? OwnerGroup { get; set; }
  public int? OwnerGroupId { get; set; }

  public Project? ParentProject { get; set; }
  public int? ParentProjectId { get; set; }

  public List<Pipeline> Pipelines { get; } = [];
  public List<Keyword> Keywords { get; } = [];
  public List<Project> SubProjects { get; } = [];
}