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C#操作数据库总结

2008-09-25 18:21 357 查看

C#操作数据库总结
2007年05月14日星期一 08:48

开发工具：Microsoft Visual Studio 2005
数据库:Microsoft SQL Server 2005
说明：这里建立的数据库名为Demo,有一个学生表Student,为操作方便起见,我只添加两个字段:studentnum和studentname.
一、SQL语句:
--create database Demo
use Demo

create table Student
(
studentnum char(14) primary key,
studentname varchar(30) not null
)

insert into Student values('20041000010201','张扬')
二、代码：
1.引入名称空间:using System.Data.SqlClient;
2.定义连接字符串,连接对象，命令对象:
private String connectionstr;
private SqlConnection connection;
private SqlCommand command;
3.在构造函数中初始化连接字符串，连接对象，命令对象

(1)初始化连接字符串：
方式① connectionstr="server=localhost;uid=sa;pwd=123456;database=Demo";
方式② connectionstr="server=127.0.0.1";Integrade Security=SSPI;database=Demo";
其中，SIMS是我要连接的数据库名.(1)中的uid 和pwd是你登录数据库的登录名和密码
注：这种连接是连接本地的数据库，若要连接局域网内其它机子上的数据库，可将方式①的"server=localhost;"改为"server=数据库所在机子的IP;"
(2)初始化连接对象
connection = new SqlConnection(connectionstr);
(3)初始化命令对象
command =new SqlCommand();
command .Connection =connection ;
4.操作数据库中的数据
(1)查询数据库中的数据
方法一：
string snum=tBstudentnum .Text .Trim ();
string str = "select * from Student where studentnum='" + snum + "'";
command .CommandText =str;
connection.Open();
if (command.ExecuteScalar() == null)
{
MessageBox.Show("您输入的学号对应的学生不存在！", "错误", MessageBoxButtons.OK,MessageBoxIcon.Error);
}
else
{
SqlDataReader sdr = command.ExecuteReader();
while (sdr.Read())
{
tBstudentnum .Text = sdr["studentnum"].ToString();
tBstudentname.Text = sdr["studentname"].ToString();
}
sdr.Close();
}
connection.Close();

方法二：
string snum=tBstudentnum .Text .Trim ();
string str = "select * from Student where studentnum='" + snum + "'";
command .CommandText =str;
connection.Open();
if (command.ExecuteScalar() == null)
{
MessageBox.Show("您输入的学号对应的学生不存在！", "错误", MessageBoxButtons.OK,MessageBoxIcon.Error);

}
else
{
SqlDataAdapter sda = new SqlDataAdapter(str,connection );
DataSet ds = new DataSet();
sda.Fill(ds, "Student");
DataTable dt = ds.Tables["Student"];
tBstudentnum.Text = dt.Rows[0]["studentnum"].ToString();
tBstudentname.Text = dt.Rows[0]["studentname"].ToString();
}
connection.Close();

(2)向数据库中添加数据
方法一:
string snum = tBstudentnum.Text.Trim ();
string sname = tBstudentname.Text.Trim();
if (snum == "" || sname == "")
{
MessageBox.Show("学生学号或姓名不能为空！", "错误", MessageBoxButtons.OK,
MessageBoxIcon.Error);
}
else
{
string insertstr="insert into Student values('"+snum +"','"+sname +"')";
command.CommandText = insertstr;
connection.Open();
command.ExecuteNonQuery();
MessageBox.Show("学生添加成功！", "提示", MessageBoxButtons.OK,
MessageBoxIcon.Information);
connection.Close();
}
方法二:
string str = "select * from Student";
string insertstr = "insert into Student values('" + snum + "','" + sname + "')";
SqlDataAdapter sda = new SqlDataAdapter(str, connection);
DataSet ds = new DataSet();
sda.Fill(ds, "Student");
DataTable dt = ds.Tables["Student"];
DataRow dr = dt.NewRow();
dr["studentnum"] = snum;
dr["studentname"] = sname;
dt.Rows.Add(dr);
sda.InsertCommand = new SqlCommand(insertstr, connection);
sda.Update(ds, "Student");
MessageBox.Show("学生添加成功！", "提示", MessageBoxButtons.OK,
MessageBoxIcon.Information);
(3)修改数据库中的数据
方法一:
string snum = tBstudentnum.Text.Trim();
string sname = tBstudentname.Text.Trim();
if (snum == "" || sname == "")
{
MessageBox.Show("学生学号或姓名不能为空！", "错误", MessageBoxButtons.OK,
MessageBoxIcon.Error);
}
else
{
string modifystr = "update Student set studentname='" + sname +
"' where studentnum='" + snum + "'";
command.CommandText = modifystr;
connection.Open();
command.ExecuteNonQuery();
MessageBox.Show("学生的姓名修改成功！", "提示", MessageBoxButtons.OK,
MessageBoxIcon.Information );
connection.Close();

方法二:
string snum = tBstudentnum.Text.Trim();
string sname = tBstudentname.Text.Trim();
if (snum == "" || sname == "")
{
MessageBox.Show("学生学号或姓名不能为空！", "错误", MessageBoxButtons.OK,
MessageBoxIcon.Error);
}
else
{
string str = "select * from Student where studentnum='" + snum + "'"; ;
string updatestr = "update Student set studentname='" + sname +
"' where studentnum='" + snum + "'";
SqlDataAdapter sda = new SqlDataAdapter(str, connection);
DataSet ds = new DataSet();
sda.Fill(ds, "Student");
DataTable dt = ds.Tables["Student"];
dt.Rows[0]["studentname"] = sname;
sda.UpdateCommand = new SqlCommand(updatestr , connection);
sda.Update(ds, "Student");
MessageBox.Show("学生姓名修改成功！", "提示", MessageBoxButtons.OK,
MessageBoxIcon.Information);
}
(4)删除数据库中的数据
方法一:
string snum = tBstudentnum.Text.Trim();
if (snum == "")
{
MessageBox.Show("学生学号不能为空！", "错误", MessageBoxButtons.OK,
MessageBoxIcon.Error);
}
else
{
string str = "select * from Student where studentnum='" + snum + "'";
string deletestr = "delete from Student where studentnum='" + snum + "'";
command.CommandText =str ;
connection.Open();
if (command.ExecuteScalar() == null)
{
MessageBox.Show("此学号对应的学生不存在！", "错误", MessageBoxButtons.OK, MessageBoxIcon.Error);
}
else
{
command.CommandText = deletestr;
command.ExecuteNonQuery();
MessageBox.Show("学生的信息删除成功！", "提示", MessageBoxButtons.OK,
MessageBoxIcon.Information);
}
connection.Close();

方二:
string str = "select * from Student where studentnum='" + snum + "'";
string deletestr = "delete from Student where studentnum='" + snum + "'";
SqlDataAdapter sda = new SqlDataAdapter(str, connection);
DataSet ds = new DataSet();
sda.Fill(ds, "Student");
DataTable dt = ds.Tables["Student"];
if (dt.Rows.Count > 0)
{
dt.Rows[0].Delete();
sda.DeleteCommand = new SqlCommand(deletestr, connection);
sda.Update(ds, "Student");
MessageBox.Show("学生信息删除成功！", "提示", MessageBoxButtons.OK,
MessageBoxIcon.Information);
}
else
{
MessageBox.Show("此学号对应的学生不存在！", "错误", MessageBoxButtons.OK, MessageBoxIcon.Error);
}

PS:以上对数据库的操作,大都从操作角度出发仅进行单一的操作,有的地方并未进行错误处理,如修改学生信息时,学号应不可能编辑等.

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