C# · 12月 27, 2021

c# – 将数据从SQL DataBase表读取到通用集合

我想从表中读取所有数据(包含3行),并将所有数据添加到通用集合中.从集合我wana绑定到gridview.

下面显示的代码可以工作,但最后一行在gridview中显示3次.可以帮助我.一个初学者

protected void Page_Load(object sender,EventArgs e){ List<Student> listid = new List<Student>(); Student stud = new Student(); sqlConnection con = new sqlConnection(“……..”); string sql = “select * from StudentInfo”; con.open(); sqlCommand cmd = new sqlCommand(sql,con); sqlDataReader dr = cmd.ExecuteReader(); while (dr.Read()) { stud.Studid = Convert.ToInt32(dr[“StudId”]); stud.StudName = dr[“StudName”].ToString(); stud.StudentDept = dr[“StudentDept”].ToString(); listid.Add(stud); } GridView1.DataSource = listid; GridView1.DataBind();}public class Student{ private int studid; public int Studid { get { return studid; } set { studid = value; } } private string studName; public string StudName { get { return studName; } set { studName = value; } } private string studentDept; public string StudentDept { get { return studentDept; } set { studentDept = value; } }

输出如下:

解决方法 你需要在循环中实例化你的对象
否则,您将收集相同的数据
所以代码应该是 protected void Page_Load(object sender,EventArgs e){ List<Student> listid = new List<Student>(); sqlConnection con = new sqlConnection(“……..”); string sql = “select * from StudentInfo”; con.open(); sqlCommand cmd = new sqlCommand(sql,con); sqlDataReader dr = cmd.ExecuteReader(); while (dr.Read()) { Student stud = new Student(); stud.Studid = Convert.ToInt32(dr[“StudId”]); stud.StudName = dr[“StudName”].ToString(); stud.StudentDept = dr[“StudentDept”].ToString(); listid.Add(stud); } GridView1.DataSource = listid; GridView1.DataBind();}

此外,使用数据读取器或直接打开连接不是一个好习惯
你应该使用using语句.

using(sqlConnection con = new sqlConnection(“connection string”)){ con.open(); using(sqlCommand cmd = new sqlCommand(“SELECT * FROM SoMetable”,connection)) { using (sqlDataReader reader = cmd.ExecuteReader()) { if (reader != null) { while (reader.Read()) { //do something } } } // reader closed and disposed up here } // command disposed here} //connection closed and disposed here