Java如何从数据库里读取一个树形表然后封装成list?

发布网友发布时间：2022-04-07 19:48

共2个回答

懂视网时间：2022-04-08 00:09

/// <summary> 2 /// 执行查询语句，返回SqlDataReader ( 注意：调用该方法后，一定要对SqlDataReader进行Close ) 3 /// </summary> 4 /// <param name="strSQL">查询语句</param> 5 /// <returns>SqlDataReader</returns> 6 public static SqlDataReader ExecuteReader(string strSQL) 7 { 8 SqlConnection connection = new SqlConnection(connectionString); 9 SqlCommand cmd = new SqlCommand(strSQL, connection); 10 try 11 { 12 connection.Open(); 13 SqlDataReader myReader = cmd.ExecuteReader(CommandBehavior.CloseConnection); 14 return myReader; 15 } 16 catch (System.Data.SqlClient.SqlException e) 17 { 18 throw e; 19 } 20 21 }

2、三层DAL层方法

 1 /// <summary>
 2  /// 把读出的数据转换成List
 3  /// </summary>
 4  public List<int> GetUserList(int hid)
 5  {
 6  string sql = " select V_UserID from UserVoters where V_HeadlineID=" + hid + "";
 7  SqlDataReader dr = DbHelperSQL.ExecuteReader(sql);
 8  List<UserVotersModel> plist = new List<UserVotersModel>();
 9  while (dr.Read())
10   {
11   UserVotersModel uvm = new UserVotersModel();
12   uvm.V_UserID = int.Parse(dr["V_UserID"].ToString());
13   plist.Add(uvm);
14   }
15  List<int> list = new List<int>();
16  for (int i = 0; i < plist.Count; i++)
17   {
18   list.Add(int.Parse(plist[i].V_UserID.ToString()));
19   }
20  return list;
21  }

3、把List当参数放到sql语句里的方法

 1 /// <summary>
 2  /// 获得未投票用户列表
 3  /// </summary>
 4  public DataSet GetNoPersonList(List<int> list)
 5  {
 6  StringBuilder strSql = new StringBuilder();
 7  if (list != null && list.Count > 0)
 8   {
 9   string listMes = string.Empty;
10   foreach (int str in list)
11   {
12   listMes += "‘" + str + "‘,";
13   }
14   strSql.Append("select U_Uid,U_Name,U_Sex,U_Phone,U_QQ from dbo.UsersInfo where U_ID not in(" + listMes.TrimEnd(‘,‘) + ") and U_Level=4 and U_Name=‘‘ ORDER BY U_ID DESC ");
15   return DbHelperSQL.Query(strSql.ToString());
16   }
17  else
18   {
19   strSql.Append(" select U_Uid,U_Name,U_Sex,U_Phone,U_QQ from dbo.UsersInfo where U_Level=4 and U_Name=‘‘ ORDER BY U_ID DESC ");
20   return DbHelperSQL.Query(strSql.ToString());
21   }
22  }

二、没有帮助类直接读取数据库

 1 /// <summary>
 2  /// 读取数据库的信息,并转换成List
 3  /// </summary>
 4  public List<MailData> GetExpiredLicense()
 5  {
 6  string connectionString = "Data Source=01;Initial Catalog=Music;Persist Security Info=True;User ID=Musicname;Password=123456";
 7  SqlConnection conn = new SqlConnection(connectionString);
 8   conn.Open();  
 9  string sql = string.Format( @" select * from Tale" );
10  
11  SqlDataAdapter da = new SqlDataAdapter(sql, connectionString);
12  DataSet ds = new DataSet();
13   da.Fill(ds);
14  List<MailData> list = new List<MailData>(); //MailData为要查询表的实体类 
15  foreach (DataRow item in ds.Tables[0].Rows)
16   {
17   list.Add(MailData.ConvertRow(item));
18   }
19  return list;
20  }

读取数据库的数据并转换成List<>

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热心网友时间：2022-04-07 21:17

首先查询的时候最好按照id的大小排序，应该是越小的是父节点，越大的是子节点，升序
才好用下面的方法
Map <Long , GroupTreeVo> temp=new HashMap<Long,GroupTreeVo>();
读取数据库数据
循环拿出，每次一条记录，相当于一个GroupTreeVo对象
每次都new 一个GroupTreeVo，数据库赋值，并存储到temp中以ID为key，对象为Value
判断是否有pid，如果有从temp中拿出父节点，设置它的children.add，
循环结束，最后，拿到temp的第一个，应该就是父节点，里面包含N多children追问亲一口