几个简单地连接数据库案例，巩固练习用

1.用户登陆，输错3次锁定角色；

string connstr = ConfigurationManager.ConnectionStrings["connstr"].ConnectionString;

using( SqlConnection conn = new SqlConnection(connstr))

{

conn.Open();

using(SqlCommand cmd = conn.CreateCommand())

{

cmd.CommandText = "select * from [user] where username = @unm";

SqlParameter[] parameters = {new SqlParameter("@unm",txtName.Text)} ;

cmd.Parameters.AddRange(parameters);

SqlDataAdapter adapter = new SqlDataAdapter(cmd);

DataSet ds = new DataSet();

adapter.Fill(ds);

DataRowCollection rows = ds.Tables[0].Rows;

string password;

string id;

//当用户名存在且不重复时间

if (rows.Count ==1)

{

password = (string)rows[0]["password"];

id = (string)rows[0]["uid"];

if (String.Equals(password,txtPassword.Text))//当用户名和密码都输入正确时

{

MessageBox.Show("login success!");

}

else//当密码输入错误时

{

cmd.CommandText = "update [user] set errortimes = errortimes+1 where uid = @id";

cmd.Parameters.Add("@id",id);

cmd.ExecuteNonQuery();

MessageBox.Show("sorry,the password is not true!");

}

int num = (int)rows[0]["errortimes"];

if (num >= 3)//如果密码输错超过3次

{

MessageBox.Show("wrong number has limited,the user is locked!");

return;

}

}

else if (rows.Count > 1) //用户名重复

{

throw new Exception("error:the username is repetition!");

}

else //用户名不存在

{

MessageBox.Show("sorry,the user is not exist!");

}

}

}

2. 省级联动查询



3.文本文件数据导入

private void txtImport_Click(object sender, RoutedEventArgs e)

{

OpenFileDialog ofd = new OpenFileDialog(); //打开浏览

ofd.Filter = "文本文件|*.txt";//文本选择过滤 txt文件

bool flag = (bool)ofd.ShowDialog();//看视频是不用转换的，不知为何。ShowDialog 表示选择的是txt文件，返回true

if(flag == false)

{

return;

}

string name = ofd.FileName; //选择文件的名称

//IEnumerable<string> lines = File.ReadLines(name,Encoding.Default); //IEnumerable 是一个集合

string[] lines = File.ReadLines(name, Encoding.Default).ToArray(); //读取选中文件内容，保存到string数组中

SqlConnection conn;

using( conn = new SqlConnection("Data Source=.;Initial Catalog=exercise;User Id=sa;Password=123456"))

{

conn.Open();

SqlCommand cmd = conn.CreateCommand();

for (int i = 0; i < lines.Count(); i++)

{

string line = lines[i];

string[] tels = line.Split('\t'); //将读取到的每一行以制表符分割成数组

Int64 tel = Convert.ToInt64(tels[0]);

string telAddr = tels[1];

//Sqlhelps.ExecuteNonQuery("insert into tel values(@tel,@telAddr)",new SqlParameter("@tel",tel),new SqlParameter("@telAddr",telAddr));

cmd.CommandText = "insert into tel(tel,telAddr) values(@tel,@add)";

cmd.Parameters.Clear();

cmd.Parameters.AddRange(new SqlParameter[]{new SqlParameter("@tel",tel),new SqlParameter("@add",telAddr)});

cmd.ExecuteNonQuery();

}

}

conn.Close();

MessageBox.Show("数据导入成功");

}

***导入到一半的时候报错，不知为何