在C＃中使用SQLite登录表单

Question

我在C＃中使用sqlite制作loginform时遇到问题。 这是代码

SQLiteConnection connectionstring;
connectionstring = " Data Source = C:\Crystal Management\Crystal Management\bin\Debug\Konaku.db; Version = 3 ";
public void LoadData()
{  
    try
    {
         SQLiteCommand SelectCommand = new SQLiteCommand("SELECT `Username`, `Password` FROM `LoginData` WHERE `Username` = '" + flatTextBox1.Text + "' AND `Password` = '" + flatTextBox2.Text + "'", connectionstring);
         SQLiteDataReader myReader;
         connectionstring.Open();
         myReader = SelectCommand.ExecuteReader();
         int count = 0;
         while (myReader.Read())
         {
             count = count + 1;
         }
         if (count == 1)
         {
             Base bs = new Base();
             bs.Show();
             this.Hide();
             connectionstring.Close();
         }
         else if (count == 0)
         {
             flatAlertBox1.kind = FlatUI.FlatAlertBox._Kind.Error;
             flatAlertBox1.Text = "data not right";
             connectionstring.Close();

         }
         else
         {

         }
     }
     catch (Exception ex) {
          MessageBox.Show(ex.Message);
          connectionstring.Close();
     }
}

这行代码显示错误

connectionstring = " Data Source = C:\\Crystal Management\\Crystal Management\bin\\Debug\\Konaku.db; Version = 3 ";

消息错误是：无法将类型'string'隐式转换为'Finisar.SQLite.SQLiteConnection'

我该怎么办？

Answer 1

应该是这样

sql_con = new SQLiteConnection
    ("Data Source=C:\Crystal Management\Crystal Management\bin\Debug\Konaku.db;Version=3;New=False;Compress=True;"); 

Answer 2

这是查询SQL的正确方法。 始终对一次性类（如SQLiteConnection，SQLiteCommand和SQLiteDataReader）使用“使用”。 使用参数化查询来避免SQL注入。

public void LoadData()
{
  try
  {
    using (var conn = new SQLiteConnection(@"Data Source=C:\Crystal Management\Crystal Management\bin\Debug\Konaku.db;Version=3"))
    {
      conn.Open();
      using (var cmd = new SQLiteCommand("SELECT Username,Password FROM LoginData WHERE Username='@username' AND Password = '@password'", conn))
      {
        cmd.Parameters.AddWithValue("@username", flatTextBox1.Text);
        cmd.Parameters.AddWithValue("@password", flatTextBox2.Text);
        using (var reader = cmd.ExecuteReader())
        {
          var count = 0;
          while (reader.Read())
          {
            count = count + 1;
          }
          if (count == 1)
          {
            Base bs = new Base();
            bs.Show();
            Hide();
          }
          else if (count == 0)
          {
            flatAlertBox1.kind = FlatUI.FlatAlertBox._Kind.Error;
            flatAlertBox1.Text = "data not right";
          }
        }
      }
    }
  }
  catch (Exception ex)
  {
    MessageBox.Show(ex.Message);
  }
}