Dapper三表联查（自表连接）去除查询结果重复

我在使用Dapper进行三表联查时，出现了查询结果重复的情况，若只对纯结果Distinct()，则会B表添加C表时产生重复

        public IEnumerable<Category> GetTCategories()
        {
            var sql = "select * from T_Category A inner join T_Category B on A.Id=B.pid Left join T_Category C on B.Id=C.pid where A.catelevel='一级'";
            Category category = null;
            Category child = null;
            var user = _dapperhelper.Query<Category, Category, Category, Category>(sql, (u, ul,ull) =>
            {
                if (category == null || category.Id != u.Id)
                {
                    category = u;
                }
                if (child == null || child.Id != ul.Id)
                {
                    child = ul;
                }
                if (ull != null) 
                {
                    child.childAuth.Add(ull);
                } 
                if (ul != null)
                {
                    category.childAuth.Add(child);                
                }
              
                return category;
            }, null, null, true, splitOn:"Id", null, null);
            return user;
        }

表结构：

实体结构：

    public class Category
    {
 
        public  int Id { get; set; }
        public  string catename { get; set; }
        public  string catelevel { get; set; }
        public  int pid { get; set; }
        public  List<Category> childAuth { get; set; } = new List<Category>();
    }

 

 

 

 表数据：

 

 查询结果：

"data": [
    {
      "id": 9,
      "catename": "大家电",
      "catelevel": "一级",
      "pid": 0,
      "childAuth": [
        {
          "id": 10,
          "catename": "电视",
          "catelevel": "二级",
          "pid": 9,
          "childAuth": [
            {
              "id": 14,
              "catename": "海信",
              "catelevel": "三级",
              "pid": 10,
              "childAuth": []
            },
            {
              "id": 15,
              "catename": "夏普",
              "catelevel": "三级",
              "pid": 10,
              "childAuth": []
            },
            {
              "id": 16,
              "catename": "创维",
              "catelevel": "三级",
              "pid": 10,
              "childAuth": []
            },
            {
              "id": 17,
              "catename": "TCL",
              "catelevel": "三级",
              "pid": 10,
              "childAuth": []
            },
            {
              "id": 18,
              "catename": "小米",
              "catelevel": "三级",
              "pid": 10,
              "childAuth": []
            }
          ]
        },
        {
          "id": 10,
          "catename": "电视",
          "catelevel": "二级",
          "pid": 9,
          "childAuth": [
            {
              "id": 14,
              "catename": "海信",
              "catelevel": "三级",
              "pid": 10,
              "childAuth": []
            },
            {
              "id": 15,
              "catename": "夏普",
              "catelevel": "三级",
              "pid": 10,
              "childAuth": []
            },
            {
              "id": 16,
              "catename": "创维",
              "catelevel": "三级",
              "pid": 10,
              "childAuth": []
            },
            {
              "id": 17,
              "catename": "TCL",
              "catelevel": "三级",
              "pid": 10,
              "childAuth": []
            },
            {
              "id": 18,
              "catename": "小米",
              "catelevel": "三级",
              "pid": 10,
              "childAuth": []
            }
          ]
        },
        {
          "id": 10,
          "catename": "电视",
          "catelevel": "二级",
          "pid": 9,
          "childAuth": [
            {
              "id": 14,
              "catename": "海信",
              "catelevel": "三级",
              "pid": 10,
              "childAuth": []
            },
            {
              "id": 15,
              "catename": "夏普",
              "catelevel": "三级",
              "pid": 10,
              "childAuth": []
            },
            {
              "id": 16,
              "catename": "创维",
              "catelevel": "三级",
              "pid": 10,
              "childAuth": []
            },
            {
              "id": 17,
              "catename": "TCL",
              "catelevel": "三级",
              "pid": 10,
              "childAuth": []
            },
            {
              "id": 18,
              "catename": "小米",
              "catelevel": "三级",
              "pid": 10,
              "childAuth": []
            }
          ]
        },

机智的我，将结果ToList()，再通过for循环，将childAuth再次去重后添加回user结果中。

        [HttpGet("[action]")]
        public IActionResult GetCategory()
        {
            var user = _userDAL.GetTCategories().Distinct().ToList();
            for (int i = 0; i < user.Count(); i++)
            {
                user[i].childAuth = user[i].childAuth.Distinct().ToList();
            }
            if (user != null)
            {
                JsonResult json = new(new { data = user, mate = new { code = 200, msg = "获取分类列表成功" } });
                return json;
            }
            else
            {
                JsonResult json = new(new { mate = new { code = 500, msg = "获取分类列表失败！" } }); ; ;
                return json;
            }
        }

 

 完美去重后结果

 "data": [
    {
      "id": 9,
      "catename": "大家电",
      "catelevel": "一级",
      "pid": 0,
      "childAuth": [
        {
          "id": 10,
          "catename": "电视",
          "catelevel": "二级",
          "pid": 9,
          "childAuth": [
            {
              "id": 14,
              "catename": "海信",
              "catelevel": "三级",
              "pid": 10,
              "childAuth": []
            },
            {
              "id": 15,
              "catename": "夏普",
              "catelevel": "三级",
              "pid": 10,
              "childAuth": []
            },
            {
              "id": 16,
              "catename": "创维",
              "catelevel": "三级",
              "pid": 10,
              "childAuth": []
            },
            {
              "id": 17,
              "catename": "TCL",
              "catelevel": "三级",
              "pid": 10,
              "childAuth": []
            },
            {
              "id": 18,
              "catename": "小米",
              "catelevel": "三级",
              "pid": 10,
              "childAuth": []
            }
          ]
        },
        {
          "id": 11,
          "catename": "空调",
          "catelevel": "二级",
          "pid": 9,
          "childAuth": [
            {
              "id": 19,
              "catename": "海尔",
              "catelevel": "三级",
              "pid": 11,
              "childAuth": []
            },
            {
              "id": 20,
              "catename": "海信",
              "catelevel": "三级",
              "pid": 11,
              "childAuth": []
            },
            {
              "id": 21,
              "catename": "科龙",
              "catelevel": "三级",
              "pid": 11,
              "childAuth": []
            },
            {
              "id": 22,
              "catename": "奥克斯",
              "catelevel": "三级",
              "pid": 11,
              "childAuth": []
            },
            {
              "id": 23,
              "catename": "三菱重工",
              "catelevel": "三级",
              "pid": 11,
              "childAuth": []
            }
          ]
        },