车牌查询 自动加载数据 相对路径

1.学会利用断电，在所在行，按住F9，添加断点，然后调试的时候，鼠标指向变量，就可以知道赋值情况，这个实验了解的是变量的路径情况

2.在程序的入口添加的相对路径，理解相对路径和绝对路径

3.SearchOption.AllDirectories搜索本文件夹和所有子目录

4.GetOrdinal()获取查询的某个属性，以名字作为索引

namespace 车牌查询
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void Form1_Load_1(object sender, EventArgs e)
        {
            using (SqlConnection conn = new SqlConnection("Data Source=DESKTOP-BEUJ3C4;Initial Catalog=DBCarId;User ID=sa;Password =2323010676;"))
            {
                conn.Open();
                SqlCommand cmd = conn.CreateCommand();
                cmd.CommandText = "delete from Table_CarId";
                cmd.ExecuteNonQuery();   //每次程序运行之前，清除数据库，可以保持数据库的不重复
            
            string filePath = Application.StartupPath; //断点，调试就可以知道StarupPath到底是什么路径

            string[] files = Directory.GetFiles(filePath, "*.txt", SearchOption.AllDirectories);//将找到的".txt"格式的文件储存到前面files数组中

                foreach (string file in files)//增强for循环，一边遍历数据，一边储存数据
                {
                    string sheng = Path.GetFileNameWithoutExtension(file);//以每个文件的名字，存到"省"中

                    string[] lines = File.ReadAllLines(file, Encoding.Default);//逐行读取数据
                    foreach (string line in lines)
                    {

                        string[] str = line.Split(' ');//以' '为分隔符
                        string shi = str[0];//索引
                        string chepai = str[1];


                        cmd.CommandText = "insert into Table_CarId(省,市,车牌) values(@sheng,@shi,@chepai)";
                        cmd.Parameters.Clear();
                        cmd.Parameters.Add(new SqlParameter("sheng", sheng));
                        cmd.Parameters.Add(new SqlParameter("shi", shi));
                        cmd.Parameters.Add(new SqlParameter("chepai", chepai));
                        cmd.ExecuteNonQuery();

                    }
                }
                cmd.CommandText = "select 省 from Table_CarId group by 省"; //自动查询省的代码，放入相应的位置
                SqlDataReader reader = cmd.ExecuteReader();
                while (reader.Read())
                {
                    cbxSheng.Items.Add(reader.GetString(reader.GetOrdinal("省")));//获取上面查询语句的某一个属性
                }
            }
            // cbxSheng.Items.Add("安徽省"); //这里知道文件里面只有三个省，提前添加
            // cbxSheng.Items.Add("江苏省");
            // cbxSheng.Items.Add("浙江省");
            

        }

    
        private void cbxSheng_SelectedIndexChanged_1(object sender, EventArgs e)
        {
            cbxShi.Items.Clear();
            cbxShi.Text = "";
            txtChepai.Text = "";

            using (SqlConnection conn = new SqlConnection ("Data Source=DESKTOP-BEUJ3C4;Initial Catalog=DBCarId;User ID=sa;Password =2323010676;"))
            {
                conn.Open();
                SqlCommand cmd = conn.CreateCommand();
                cmd.CommandText = "select * from Table_CarId where 省=@sheng";
                cmd.Parameters.Add(new SqlParameter("sheng", cbxSheng.Text));
                SqlDataReader reader = cmd.ExecuteReader();
                while (reader.Read())
                {
                    cbxShi.Items.Add(reader.GetString(reader.GetOrdinal("市")));
                }
            }    
        }

        private void btnSelect_Click_1(object sender, EventArgs e)
        {
            using (SqlConnection conn = new SqlConnection("Data Source=DESKTOP-BEUJ3C4;Initial Catalog=DBCarId;User ID=sa;Password =2323010676;"))
            {
                conn.Open();
                SqlCommand cmd = conn.CreateCommand();
                cmd.CommandText = "select * from Table_CarId where 市=@shi";
                cmd.Parameters.Add(new SqlParameter("shi", cbxShi.Text));
                SqlDataReader reader = cmd.ExecuteReader();
                if (reader.Read())
                {
                    txtChepai.Text = reader.GetString(reader.GetOrdinal("车牌"));
                }
            }   
        }

        private void cbxShi_SelectedIndexChanged(object sender, EventArgs e)
        {
            txtChepai.Text = "";
        }
    }
}